Karps Cell and Molecular Biology 8th Edition by Karp – Test Bank

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Package Title: Test Bank

Course Title: Karp7e

Chapter Number: 5

 

 

Question Type: Multiple Choice

 

 

1) Which of the following is not found in a reducing atmosphere?

 

  1. a) H2
  2. b) NH3
  3. c) O2
  4. d) H2O
  5. e) Both O2 and H2O

 

Answer: c

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

2) What advantage do the cristae confer on the mitochondria?

 

  1. a) They allow the mitochondria to shrink.
  2. b) They greatly increase the surface area for aerobic respiration machinery.
  3. c) They confer resiliency on the cells.
  4. d) They allow swelling of mitochondria.
  5. e) They activate the matrix.

 

Answer: b

 

Difficulty: Easy

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

3) The balance between fusion and fission is likely a major determinant of __________.

 

  1. a) number
  2. b) length
  3. c) color
  4. d) degree of interconnection
  5. e) number, length and degree of interconnection

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

4) When fusion of mitochondria becomes more frequent than fission, the mitochondria tend to become __________.

 

  1. a) more elongated
  2. b) more interconnected
  3. c) more numerous
  4. d) more distinct
  5. e) more elongated and more interconnected

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

5) When fission of mitochondria becomes more frequent than fusion, the mitochondria tend to become __________.

 

  1. a) more elongated
  2. b) more interconnected
  3. c) more numerous
  4. d) more distinct
  5. e) more numerous and more distinct

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

6) The presence of Ca2+ ion transport molecules in the inner mitochondrial membrane is consistent with the mitochondrion’s role in _______.

 

  1. a) muscle contraction
  2. b) regulating cytosolic Ca2+ ion concentration
  3. c) ATP manufacture
  4. d) ADP manufacture
  5. e) control of membrane fusion

 

Answer: b

 

Difficulty: Easy

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

7) Mitochondria are sites of the __________.

 

  1. a) synthesis of certain amino acids
  2. b) synthesis of heme groups
  3. c) uptake of Ca2+ ions
  4. d) release of Ca2+ ions
  5. e) All of these are correct.

 

Answer: e

 

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

8) Which of the following is(are) regulated by mitochondria?

1) intracellular levels of Ca2+ ions

2) intracellular levels of K+ ions

3) process of cell death

4) process of closure

 

  1. a) 1
  2. b) 2
  3. c) 3
  4. d) 4
  5. e) 1 and 3

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

9) Which of the following regulate intracellular levels of Ca2+ ions?

 

  1. a) Golgi apparatus
  2. b) ribosomes
  3. c) endoplasmic reticulum
  4. d) mitochondria
  5. e) both endoplasmic reticulum and mitochondria

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

10) What are the two interconnected domains of the inner mitochondrial membrane?

 

  1. a) inner boundary membrane, cristae
  2. b) central boundary membrane, cristae
  3. c) cristae boundary membrane, outer boundary membrane
  4. d) inner boundary membrane, outer boundary membrane
  5. e) cristae, matrix

 

Answer: a

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

11) What is defined as a domain of the inner mitochondrial membrane that is present within the interior of the mitochondrion as a series of invaginated membranous sheets?

 

  1. a) inner boundary membrane
  2. b) outer boundary membrane
  3. c) cristae
  4. d) matrix
  5. e) pseudopodia

 

Answer: c

 

Difficulty: Easy

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

12) The inner boundary membrane is particularly rich in which of the following?

 

  1. a) protons
  2. b) proteins responsible for the import of mitochondrial proteins
  3. c) Krebs cycle enzymes
  4. d) enzymes of the glycolytic pathway
  5. e) glycosaminoglycans

 

Answer: b

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

13) Which lipid is known for playing an important role in facilitating the activity of proteins involved in ATP synthesis?

 

  1. a) diphosphatidylglycerol
  2. b) phosphatidyl inositol
  3. c) phosphatidic acid
  4. d) cardiolipin
  5. e) both diphosphatidylglycerol and cardiolipin

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

14) What evidence suggests that the inner mitochondrial membrane has evolved from a bacterial plasma membrane?

1) the presence of porins in both membranes

2) the virtual absence of cholesterol from both membranes

3) both membranes being rich in cardiolipin

4) both membranes being rich in diphosphatidylglycerol

 

  1. a) 1
  2. b) 2
  3. c) 3
  4. d) 4
  5. e) 2, 3 and 4

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

15) What evidence suggests that the outer mitochondrial membrane has evolved from the outer membrane that is present as part of the cell wall of certain bacteria?

1) the presence of porins in both membranes

2) the virtual absence of cholesterol from both membranes

3) both membranes being rich in cardiolipin

4 both membranes being rich in diphosphatidylglycerol

 

  1. a) 1
  2. b) 2
  3. c) 3
  4. d) 4
  5. e) 1 and 4

 

Answer: a

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

16) From what does the mitochondrial RNA polymerase appear to have evolved?

1) the multisubunit RNA polymerase found in prokaryotic cells

2) the multisubunit RNA polymerase found in eukaryotic cells

3) the multisubunit RNA polymerase found in bacterial viruses (bacteriophage)

4) the single subunit RNA polymerase found in bacterial viruses (bacteriophage)

 

  1. a) 1
  2. b) 2
  3. c) 3
  4. d) 4
  5. e) 1 and 2

 

Answer: d

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

 

 

17) In what ways can pyruvate and NADH be metabolized?

 

  1. a) fermentation, hydrolysis of PGAL
  2. b) condensation of PGAL and fermentation
  3. c) aerobic processes using Krebs cycle, fermentation
  4. d) anaerobic processing using Krebs cycle, fermentation
  5. e) aerobic processing using Krebs cycle, hydrolysis of PGAL

 

Answer: c

 

Difficulty: Hard

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion

 

 

18) How many carbons from 13 original glucose molecules enter the Krebs cycle in the presence of oxygen?

 

  1. a) 0
  2. b) 13
  3. c) 26
  4. d) 52
  5. e) 78

 

Answer: d

 

Difficulty: Medium

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion

 

 

19) How many carbons from 13 original glucose molecules enter the Krebs cycle in the absence of oxygen?

 

  1. a) 0
  2. b) 13
  3. c) 26
  4. d) 52
  5. e) 78

 

Answer: a

 

Difficulty: Medium

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion

 

 

20) What happens to the carbons of pyruvate that do not enter the Krebs cycle?

 

  1. a) They are converted to carbohydrates.
  2. b) They are converted to CO2.
  3. c) They are converted to glucose.
  4. d) They are converted to ATP.
  5. e) They are converted to carbon monoxide (CO).

 

Answer: b

 

Difficulty: Medium

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion

 

 

21) What molecule is responsible for conveying 2 carbons from pyruvate to the Krebs cycle?

 

  1. a) Coenzyme G
  2. b) Coenzyme A
  3. c) Acetate
  4. d) pyruvate
  5. e) oxaloacetate

 

Answer: b

 

Difficulty: Easy

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion

 

 

22) Which component involved in the Krebs (TCA) cycle is bound to the inner mitochondrial membrane?

 

  1. a) oxaloacetate
  2. b) acetyl CoA
  3. c) succinate dehydrogenase
  4. d) succinate
  5. e) succinyl CoA

 

Answer: c

 

Difficulty: Easy

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion

 

 

23) Where are most of the enzymes of the Krebs cycle located?

 

  1. a) in the intercristal space
  2. b) on the cristae
  3. c) on the ribosomes
  4. d) in the soluble phase of the mitochondrial matrix
  5. e) in the intermembrane space

 

Answer: d

 

Difficulty: Easy

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion

 

 

24) To what is the 2-carbon fragment of acetyl CoA added to make citric acid at the start of the Krebs cycle?

 

  1. a) oxaloacetate
  2. b) citric acid
  3. c) succinate
  4. d) -ketoglutarate
  5. e) isocitric acid

 

Answer: a

 

Difficulty: Easy

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion

 

 

25) What is the terminal electron acceptor of the electron transport chain?

 

  1. a) water
  2. b) O2
  3. c) CO2
  4. d) CO
  5. e) glucose

 

Answer: b

 

Difficulty: Easy

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

26) How is the energy used to make ATP via the electron transport chain generated?

 

  1. a) The energy from electrons bound to reduced coenzymes is used to create a steep electrochemical gradient.
  2. b) Electrons bound to NADH are used to generate a H+ ion gradient across the inner mitochondrial membrane.
  3. c) Electrons bound to FADH2 are used to generate a proton gradient across the inner mitochondrial membrane.
  4. d) Electrons bound to NADH are used to generate a proton gradient across the inner mitochondrial membrane.
  5. e) All of these are correct.

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

27) What is the name of the process by which the electron transport chain generates the electrochemical gradient that drives ATP production in the mitochondrion?

 

  1. a) osmosis
  2. b) diffusion
  3. c) facilitated diffusion
  4. d) chemiosmosis
  5. e) frusion

 

Answer: d

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

28) On average, how many ATPs would be made if 4 NADH and 6 FADH2 molecules donated their high-energy electrons to the mitochondrial electron transport chain?

 

  1. a) 10
  2. b) 24
  3. c) 12
  4. d) 30
  5. e) 20

 

Answer: b

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

29) How do mitochondria generate and store the energy used to produce most of the ATP made during aerobic respiration?

 

  1. a) by producing heat
  2. b) by generating a heat gradient
  3. c) by generating an ionic (electrochemical) gradient
  4. d) by generating a Cl ion gradient
  5. e) by generating a Na+ ion gradient

 

Answer: c

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

30) ___________ exhibit lower electron affinity.

 

  1. a) Strong oxidizing agents
  2. b) Strong elucidating agents
  3. c) Strong reducing agents
  4. d) Weak reducing agents
  5. e) Weak eliminating agents

 

Answer: c

 

Difficulty: Hard

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

31) Spontaneous oxidation-reduction (redox) reactions are accompanied by ________.

 

  1. a) a gain of heat energy
  2. b) a loss of free energy
  3. c) a gain of free energy
  4. d) a loss of heat energy
  5. e) a gain of heat loss

 

Answer: b

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

32) The direct formation of ATP by the transfer of a phosphate group from a donor molecule to ADP is called ________.

 

  1. a) substrate-level phosphorylation
  2. b) oxidative phosphorylation
  3. c) cyclic photophosphorylation
  4. d) noncyclic photophosphorylation
  5. e) indigenous phosphorylation

 

Answer: a

 

Difficulty: Easy

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

33) Which enzyme of the Krebs (TCA) cycle is different from the others with respect to its location and where is it located?

 

  1. a) succinate dehydrogenase, mitochondrial matrix
  2. b) malate dehydrogenase, mitochondrial matrix
  3. c) succinate dehydrogenase, inner mitochondrial membrane
  4. d) malate dehydrogenase, inner mitochondrial membrane
  5. e) succinate dehydrogenase, intermembrane space

 

Answer: c

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

34) What type of electron carrier has a prosthetic group derived from vitamin B2?

 

  1. a) flavoproteins
  2. b) cytochromes
  3. c) copper atom containing carriers
  4. d) ubiquinone
  5. e) iron-sulfur proteins

 

Answer: a

 

Difficulty: Easy

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

35) What type of electron carrier has a prosthetic group derived from riboflavin?

 

  1. a) flavoproteins
  2. b) cytochromes
  3. c) copper atom containing carriers
  4. d) ubiquinone
  5. e) iron-sulfur proteins

 

Answer: a

 

Difficulty: Easy

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

36) What is another name from for partially reduced ubiquinone?

 

  1. a) ubiquinone
  2. b) ubisemiquinone
  3. c) ubiquinol
  4. d) ubiquinde
  5. e) ubiquinate

 

Answer: b

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

37) What is the final electron acceptor in the electron transport chain?

 

  1. a) water
  2. b) carbon dioxide
  3. c) carbon monoxide
  4. d) hydrogen
  5. e) oxygen

 

Answer: e

 

Difficulty: Easy

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

38) What is formed when electrons reach the bottom of the mitochondrial electron transport chain and bind to the final electron acceptor?

 

  1. a) water
  2. b) carbon dioxide
  3. c) carbon monoxide
  4. d) hydrogen
  5. e) oxygen

 

Answer: a

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

39) How do many potent respiratory poisons exert their effect?

 

  1. a) They break down oxygen.
  2. b) They bind to electrons.
  3. c) They bind to the cytochrome oxidase catalytic site.
  4. d) They bind to oxygen.
  5. e) They denature the inner mitochondrial membrane.

 

Answer: c

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

40) You are trying to figure out an electron transport pathway including the following electron transport molecules: B, K, T, Q and X.  You do so by employing inhibitors for various steps in the process.  When you do, you get the following results:

 

Inhibitor                      Electron Transport Molecules Trapped in Reduced Form

Ticin                            Q & K

Digitin                         K

Estin                            T, K, Q & B

Lucin                           Q, K & T

 

What is the order of the molecules (the pathway) in the electron transport chain suggested by the above data from the most reduced to the least reduced molecule?

 

  1. a) K —> T —> B —> Q —> X
  2. b) K —> X —> B —> Q —> T
  3. c) K —> Q —> T —> B —> X
  4. d) X —> B —> T —> Q —> K
  5. e) T —> B —> K —> Q —> X

 

Answer: c

 

Difficulty: Hard

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

41) Why must the process by which cytochrome oxidase works be efficient?

 

  1. a) If it is not, mitochondria will shrink.
  2. b) If it is not, mitochondria will swell and burst.
  3. c) The process deals with very dangerous substances, which, if released, could damage virtually every cell macromolecule.
  4. d) If it is not the mitochondria could denature.
  5. e) All of these are correct.

 

Answer: c

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

42) What is unusual about the way that H+ ions are transported across the inner mitochondrial membrane as compared to the movement of other ions like Na+ and Cl ions?

 

  1. a) Na+ and Cl ions must traverse the full distance, but H+ ions materialize on the other side of the membrane.
  2. b) Na+ and Cl ions must traverse the full distance, but H+ ions can hop through a channel by exchanging themselves with other protons found along the pathway.
  3. c) Na+ and Cl ions can hop through a channel by exchanging themselves with other similar ions found along the pathway, but H+ ions must traverse the full distance.
  4. d) Na+ and Cl ions must traverse the full distance, but H+ ions must only go halfway.
  5. e) Na+ and Clions must traverse the full distance, but H+ ions must change into neutrons first.

 

Answer: b

 

Difficulty: Hard

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

43) Pathways in which H+ ions can “hop” through a channel by exchanging themselves with other protons present along the pathway are called ___________.

 

  1. a) proton-conduction pathways
  2. b) electrical wires
  3. c) proton wires
  4. d) proton conveyer belt
  5. e) proton-conduction pathways and proton wires

 

Answer: e

 

Difficulty: Hard

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

 

44) Electrochemical gradients have both a(n) _________ and a(n) __________ component.

 

  1. a) concentration, acidic
  2. b) acidic, electrical
  3. c) concentration, basic
  4. d) concentration, electrical
  5. e) acidic, basic

 

Answer: d

 

Difficulty: Easy

Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.

Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force

 

 

45) Electrochemical gradients have both a(n) _________ and a(n) _________ component.

 

  1. a) concentration, acidic
  2. b) acidic, electrical
  3. c) concentration, basic
  4. d) chemical, voltage
  5. e) acidic, basic

 

Answer: d

 

Difficulty: Easy

Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.

Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force

 

 

46) Why did DNP kill patients who took the drug to help them lose weight?

 

  1. a) It caused the patients to oxidize their fat stores in a vain attempt to maintain normal ATP levels.
  2. b) It blocked hemoglobin.
  3. c) It caused an infection.
  4. d) It caused total paralysis.
  5. e) It prevented the patients from breathing.

 

Answer: a

 

Difficulty: Easy

Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.

Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force

 

 

47) What is the purpose of uncoupling proteins in mammalian brown adipose tissue?

 

  1. a) They give the tissue its color.
  2. b) They help the tissue expand and contract when needed.
  3. c) They function as a source of heat production during exposure to cold temperatures.
  4. d) They allow the production of a larger number of ATPs per glucose.
  5. e) They allow muscles to contract more efficiently.

 

Answer: c

 

Difficulty: Medium

Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.

Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force

 

 

48) The F0 base of ATP synthase serves as a(n) ______.

 

  1. a) enzyme that synthesizes ATP
  2. b) enzyme that hydrolyzes ATP
  3. c) channel that conducts protons from the intermembrane space back to the matrix
  4. d) channel that conducts protons from the matrix back to the intermembrane space
  5. e) proton pump

 

Answer: c

 

Difficulty: Medium

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

49) The energy released by proton movement through ATP synthase ___________.

 

  1. a) directly phosphorylates ADP to ATP
  2. b) increases the binding affinity of the active site for the ATP product
  3. c) directly phosphorylates ATP to ADP
  4. d) decreases the binding affinity of the active site for the ATP product
  5. e) directly phosphorylates AMP to ATP

 

Answer: d

 

Difficulty: Medium

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

50) The energy expended during the formation of ATP by ATP synthase is required to _______.

 

  1. a) attach the phosphate group to ADP
  2. b) attach the phosphate group to ATP
  3. c) release the tightly bound ATP from the ATP synthase catalytic site
  4. d) attach the tightly bound ATP to the ATP synthase catalytic site
  5. e) move protons against their gradient

 

Answer: c

 

Difficulty: Medium

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

51) How many catalytic sites does ATP synthase possess?

 

  1. a) 1
  2. b) 2
  3. c) 3
  4. d) 6
  5. e) 4

 

Answer: c

 

Difficulty: Medium

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

52) The three catalytic sites of ATP synthase ___________.

 

  1. a) have different substrate binding affinities
  2. b) have different product binding affinities
  3. c) at any one time are present in different conformations
  4. d) pass sequentially through their three different conformations
  5. e) All of these are correct.

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

53) The L conformation of ATP synthase catalytic sites ________.

 

  1. a) has a very low affinity for nucleotides
  2. b) loosely binds AMP and an inorganic phosphate group
  3. c) has a very low affinity for proteins
  4. d) binds ATP, ADP and inorganic phosphate groups tightly
  5. e) loosely binds ADP and an inorganic phosphate group

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

54) It has been shown that one part of ATP synthase rotates relative to another part of the enzyme.  This phenomenon is referred to as ________.

 

  1. a) turning catalysis
  2. b) revolutionary catalysis
  3. c) rotational catalysis
  4. d) rotatalysis
  5. e) revolalysis

 

Answer: c

 

Difficulty: Easy

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

55) What drives the rotation of the F1 head of ATP synthase?

 

  1. a) proton movement from intermembrane space to the matrix
  2. b) proton movement from the matrix to the intermembrane space
  3. c) ATP hydrolysis
  4. d) ATP condensation
  5. e) proton movement from the cytoplasm to the intermembrane space

 

Answer: a

 

Difficulty: Easy

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

56) Which of the statements below served as evidence that rotational catalysis occurs in ATP synthase?

 

  1. a) movement was directly observed in the electron microscope
  2. b) a fluorescently labeled actin filament attached to the enzyme’s  subunit was seen to rotate when ATP was added to the enzyme which was fixed to a cover slip
  3. c) circular dichroism revealed the movement
  4. d) an inhibitor stopped the enzyme movement
  5. e) atomic force microscopy showed the movement

 

Answer: b

 

Difficulty: Medium

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

57) In the experiment that demonstrated that rotational catalysis occurs, a fluorescently labeled actin filament attached to the ATP synthase enzyme’s  subunit was seen to rotate when ATP was added to the enzyme, which was fixed to a cover slip.  With each step in the rotational catalysis, how much could the actin filament be seen to rotate?

 

  1. a) 0°
  2. b) 360°
  3. c) 120°
  4. d) 90°
  5. e) 3°

 

Answer: c

 

Difficulty: Hard

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

58) What energy source other than ATP hydrolysis do mitochondria, unlike most other organelles, routinely use to power their activities?

 

  1. a) ADP hydrolysis
  2. b) proton-motive force
  3. c) Na+ ion gradient
  4. d) K+ ion gradient
  5. e) Ca2+ gradient

 

Answer: b

 

Difficulty: Easy

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

59) Which activity below is not thought to be driven by the proton-motive force?

 

  1. a) formation of the spindle
  2. b) ADP and inorganic phosphate uptake into the mitochondrion in exchange for ATP and H+, respectively
  3. c) uptake of Ca2+ ions into the mitochondrion
  4. d) the events of mitochondrial fusion
  5. e) uptake of specifically targeted proteins into the mitochondrion from the matrix

 

Answer: a

 

Difficulty: Easy

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

60) Which molecule below plays a key role in regulating the rate of glycolysis and Krebs cycle by regulating the activity of key enzymes?

 

  1. a) ADP
  2. b) inorganic phosphate
  3. c) ATP
  4. d) molecular oxygen
  5. e) gaseous nitrogen

 

Answer: c

 

Difficulty: Easy

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

61) Which molecule below plays a key role in regulating respiratory rate in the mitochondrion?

 

  1. a) ADP
  2. b) inorganic phosphate
  3. c) ATP
  4. d) molecular oxygen
  5. e) gaseous nitrogen

 

Answer: a

 

Difficulty: Easy

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

 

 

62) An unusual type of phospholipid is found in the myelin sheath that insulates brain axons; abnormalities in the synthesis of this phospholipid can lead to severe neurological dysfunction.  What are these phospholipids called?

 

  1. a) plasmins
  2. b) sphingolipids
  3. c) plasmalogens
  4. d) insulins
  5. e) luciferases

 

Answer: c

 

Difficulty: Easy

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

 

 

63) Which of the following is true of peroxisomes?

 

  1. a) Peroxisomes may contain a dense, crystalline core of oxidative enzymes.
  2. b) Peroxisomes contain more than 50 enzymes involved in diverse activities.
  3. c) Peroxisomes contain enzymes that oxidize very-long-chain fatty acids.
  4. d) Peroxisomes contain the enzyme luciferase, which generates the light emitted by fireflies.
  5. e) All of these are correct.

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

 

 

64) What properties do mitochondria share with peroxisomes?

 

  1. a) Both form by splitting from preexisting organelles, using some of the same proteins to accomplish the feat.
  2. b) Both import preformed proteins from the cytosol.
  3. c) Both engage in similar types of oxidative metabolism.
  4. d) At least one enzyme is found in the mitochondria of some mammals and the peroxisomes of others.
  5. e) All of these are correct.

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

 

 

65) Peroxisomal enzymes __________.

1) produce hydrogen peroxide

2) break down hydrogen peroxide

3) include catalase

 

  1. a) 1
  2. b) 2
  3. c) 3
  4. d) 1 and 2
  5. e) 1, 2 and 3

 

Answer: e

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

 

 

66) Which organelle below is not found in both plants and animals?

 

  1. a) cell membrane
  2. b) mitochondria
  3. c) peroxisomes
  4. d) glyoxysomes
  5. e) vacuoles

 

Answer: d

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

 

 

Question Type: Essay

 

 

67) How can biologists be sure that the appearance of photosynthetic organisms preceded that of aerobic organisms in the Earth’s evolutionary history?

 

Answer:

 

Difficulty: Easy

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

Solution: Since aerobic organisms require the presence of oxygen in the atmosphere to serve as the final electron acceptor in the electron transport chain, photosynthetic organisms must have appeared first.  The earliest atmospheres on Earth (during the first 2 billion years) were highly reduced and contained no free oxygen, but did contain hydrogen gas (H2), ammonia (NH3) and water (H2O). Aerobic respiration could not have occurred in such an atmosphere.  When photosynthetic organisms, the cyanobaccteria, appeared about 2.7 billion years ago, they started producing oxygen as a byproduct and thus produced an atmosphere that contained significant amounts of free molecular oxygen within a few hundred million years.  Only then could aerobic organisms have evolved.

 

 

68) Observations of two different cell types indicate a couple of differences in their mitochondria.  Cell type 1 has 2-3 times the mitochondria of Cell Type 2.  The mitochondria in Cell Type 1 are also larger, contain more cristae and the cristae extend farther across the mitochondria than in Cell Type 2.  Which cell type is likely to have more extensive energy requirements?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.

Section Reference: Section 5.1 Mitochondrial Structure and Function

Solution: Since ATP synthase is located on the cristae, cells that have more cristae with a larger surface area will be able to make more ATP to satisfy those energy requirements.  The number of cristae and their surface area in the cell can be increased by any combination of the following strategies: increasing the number of mitochondria, increasing the number of cristae packed into each mitochondrion, increasing the size of cristae so that they extend all the way across the mitochondrion and increasing the size of each mitochondrion.  Consequently, Cell Type 1 probably has the largest energy requirements.

 

 

69) How many carbons from an original glucose molecule get into the TCA cycle?  What happens to the carbons that do not enter the cycle?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion

Solution: Four (4) carbons from an original 6-C glucose get into the TCA cycle, 2 from each of two 3-C pyruvates.  The other two carbons are removed from the chain and released as carbon dioxide.

 

 

70) Given the overall equation for respiration: C6H12O6 + 6O2 <—> 6CO2 + 6H2O, at what point in respiration are the reactants used up and the products made?

 

Answer:

 

Difficulty: Hard

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

Solution: Glucose is used up at the first step in glycolysis when a phosphate group is transferred to it.  Oxygen (O2) is used up when it acts as the final electron acceptor at the end of the electron transport chain, thus producing water.  Carbon dioxide is produced as a carbon atom is removed from pyruvate before the entry of two of its carbon atoms into the TCA cycle and at various points in the cycle as carbons are removed from some of the TCA metabolites.

 

 

71) You are studying the enzyme kinetics of enzymes in the TCA cycle.  You add a molecule to the mixture that appears to act as a competitive inhibitor of one of the enzymes.  At first, you cannot tell which enzyme is inhibited, but you can tell that it is bound to the inner mitochondrial membrane.  Can you guess which TCA enzyme you have inhibited and how do you know?

 

Answer: The enzyme is succinate dehydrogenase since it is the only enzyme of the TCA cycle that is bound to the inner mitochondrial membrane. The other TCA enzymes are located in the mitochondrial matrix.

 

Difficulty: Hard

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the MitochrondrionSolution: The enzyme is succinate dehydrogenase since it is the only enzyme of the TCA cycle that is bound to the inner mitochondrial membrane.  The other TCA enzymes are located in the mitochondrial matrix.

 

 

72) Why are molecules that block oxidative phosphorylation and the electron transfer chain such dangerous and potentially deadly poisons?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.

Section Reference: Section 5.2 Oxidative Metabolism in the MitochrondrionSolution: By blocking the electron transport chain, the electron transport chain backs up.  This will eventually prevent the recycling of NADH and FADH2.  Since these molecules are present in finite amounts, a lack of recycling will place most of them in the reduced state.  Since the oxidized forms of NADH (NAD+) and FAD are needed for the TCA cycle and glycolysis to occur, it will be unavailable in the presence of electron transport inhibitors and little or no ATP will be made.  Consequently, the organism will die.

 

 

73) There are four large complexes of electron transport molecules in the inner mitochondrial membrane.  There are also two smaller proteins that carry electrons between the complexes.  What is a possible reason for the much smaller size of these shuttle proteins, cytochrome c and ubiquinone?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

Solution: Cytochrome c and ubiquinone are smaller because they must shuttle electrons between the complexes.  They would be unable to diffuse through the membrane efficiently if they were extremely large like the complexes.

 

 

74) A doctor in a hospital emergency room sees an obese patient who has come into the emergency room.  He has been losing weight rapidly but complains that he has lost energy and is tired most of the time.  During his interview with the patient, the doctor thinks he has discovered what is causing the man’s condition.  What do you think he has found?

 

Answer:

 

Difficulty: Hard

Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.

Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force

Solution: He probably discovers that the patient has taken a self-prescribed diet pill called 2, 4 – dinitrophenol (DNP), a chemical that was used in the 1920s for this very purpose.  It was found to be dangerous, since a number of people using it died.  It is dangerous because it uncouples the production of ATP from the process of glucose oxidation.  While glucose is broken down, no ATP is made and it becomes difficult to keep vital processes going.

 

 

75) A preparation of submitochondrial particles is made.  The particles are able to oxidize substrates, generate a proton gradient and make ATP.  If the particles are treated with urea, what happens?  If DNP is added, what happens?  How does DNP make the inner mitochondrial membrane permeable to protons?

 

Answer:

 

 

Difficulty: Hard

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

Solution: Urea treatment removes the F1 spheres from ATP synthase.  As a result, the membrane is no longer able to maintain the proton gradient.  Protons leak out of the F0 base piece in an uncontrolled fashion when the headpiece is removed and ATP cannot be made because the headpiece that makes it is gone. DNP also uncouples ATP production from electron transport.  It causes the membrane to become permeable to protons and thus dissipates the proton gradient, making ATP production by ATP synthase impossible.  DNP combines with protons and, because of its lipid solubility, carries the protons across the inner mitochondrial membrane down their electrochemical gradient.

 

 

76) You treat some cells with DNP and discover that ATP production ceases.  Upon closer examination, you also note that the number of calcium ions sequestered in the mitochondrion decreases.  Please explain.

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.

Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force

Solution: DNP dissipates the proton gradient generated by electron transport, and this prevents ATP production.  The gradient also appears to play a role in moving calcium ions into the mitochondrion.  If the gradient is dissipated, the mitochondrion will be unable to move calcium ions into it, and thus it will not be able to maintain calcium ion sequestration.

 

 

77) You are a world-wide expert in mitochondria.  If an investigator tells you that he wishes to study mitochondrial uncoupling proteins, what kind of organism would you suggest he use as a source of the protein?  What is the function of brown adipose tissue?  Humans lose brown fat deposits as they age.  How does that happen and how do humans maintain body temperature when the brown fat is gone?  Uncoupling protein (UCP) isoforms are found in cells of the nervous system.  While their roles are debated, what is the most prominent hypothesis that may explain their function?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.

Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force

Solution: Uncoupling protein is most plentiful in brown fat.  Such tissue is found in newborn mammals, hibernating animals or animals acclimated to cold environments. Brown adipose tissue functions as a source of heat production during exposure to cold temperatures.  Human infants also rely on brown fat deposits to maintain body temperature.  Brown fat cells are largely lost as we grow up.  When humans are older they are dependent on muscle contractions (shivering) to generate body heat.  It has been suggested that UCPs in the inner mitochondrial membrane may prevent the build-up of an excessively large proton-motive force.  If such a high-energy state were to form, it could block the passage of electrons through the respiratory complexes, leading to the leakage of electrons and the production of reactive oxygen radicals.

 

 

78) Rat liver mitochondria are isolated and placed in an assay medium.  What happens to the pH of the medium when the medium is kept anaerobic?  What happens when O2-saturated saline is added to the mixture?

 

Answer:

 

Difficulty: Hard

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

Solution: When the medium is kept anaerobic, the pH of the medium stays constant.  When O2 is injected into the mixture, the mitochondria start doing aerobic respiration.  Protons are pumped out of the matrix and the medium becomes acidified, decreasing the pH.

 

 

79) You prepare red blood cell ghosts with a very high internal potassium ion concentration and a very high external sodium ion concentration, higher than normally exists in the body.  The red blood cell ghost also contains ADP and inorganic phosphate ions in the interior and the Na+-K+ pump in the membrane.  What happens?

 

Answer:

 

Difficulty: Hard

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

Solution: Potassium ions move out of the ghost and sodium ions move into the ghost down their gradients, rather than up as would normally occur in a living cell.  The movement of the ions causes ATP to be synthesized rather than hydrolyzed.

 

 

80) In addition to driving the synthesis of ATP, what other processes in the mitochondria are driven by the proton-motive force?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.

Section Reference: Section 5.5 The Machinery for ATP Formation

Solution: The proton-motive force drives the uptake of ADP and Pi into the mitochondria in exchange for ATP and H+, respectively.  It may also be used as the source of energy to “pull” calcium ions into the mitochondrion; it may be used to drive the events of mitochondrial fusion and to cause specifically targeted polypeptides to enter the mitochondrion from the matrix.

 

 

81) What are some of the diverse activities in which the enzymes found in peroxisomes are involved?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: These enzymes are involved in the oxidation of very-long-chain fatty acids (VLCFAs, ones whose chain typically contains 24 to 26 carbons) and the synthesis of plasmalogens, an unusual class of phospholipids in which one of the fatty acids is linked to glycerol by an ether linkage rather than an ester linkage.  Plasmalogens are very abundant in the myelin sheaths that insulate axons in the brain.  Abnormalities in the synthesis of these molecules can lead to severe neurological dysfunction.  The enzyme luciferase, which generates the light emitted by fireflies, is also a peroxisomal enzyme.

 

 

82) What properties do mitochondria and peroxisomes have in common?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: They both form by splitting from preexisting organelles, using some of the same proteins to accomplish the feat. Both types of organelles import preformed proteins from the cytosol, and both engage in similar types of oxidative metabolism.  In fact, at least one enzyme, alanine/glyoxylate aminotransferase is found in the mitochondria of some mammals (like cats and dogs) and the peroxisomes of other mammals (like rabbits and humans).

 

 

83) Where did peroxisomes get their name?  How is the toxic hydrogen peroxide generated by these organelles disposed of?  What is the specialized type of peroxisome found in plant seedlings and what specialized function do these organelles perform?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: Their name is derived from the fact that they are the site of the synthesis and degradation of hydrogen peroxide, a highly reactive and toxic oxidizing agent.  Hydrogen peroxide is produced by a number of peroxisomal enzymes, including urate oxidase, glycolate oxidase and amino acid oxidases, which utilize molecular oxygen to oxidize their respective substrates.  The hydrogen peroxide generated in these reactions is rapidly broken down by the enzyme catalase, which is present in high concentrations in these organelles.  The specialized peroxisome is called a glyoxysome.  Plant seedlings rely on stored fatty acids to provide the energy and material to form a new plant.  One of the primary metabolic activities in germinating seedlings is the conversion of stored fatty acids to carbohydrate.  When stored fatty acids are disassembled, acetyl CoA is generated.  The acetyl CoA condenses with oxaloacetate to form citrate.  Citrate is then converted to glucose by a series of enzymes of the glyoxylate cycle localized in the glyoxysome.

 

 

84) Which reaction releases more free energy – the removal of a phosphate group from creatine phosphate or the removal of a phosphate group from ATP?

 

Answer:

 

Difficulty: Hard

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

Solution: The removal of a phosphate group from creatine phosphate releases more free energy than the removal of a phosphate group from ATP.  In fact, creatine phosphate gives off enough free energy to drive the production of ATP, a reaction that actually happens.  ATP’s conversion to ADP, however, does not give off enough free energy to phosphorylate creatine.

 

 

85) You have isolated some muscle cells in a tissue culture system.  You are able to get them to contract in culture.  If you add an inhibitor of the electron transport system to these cells, they do not contract quite as much, but they still contract noticeably.  What kind of muscle fiber type are you employing?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

Solution: These muscle fibers are most likely to be fast twitch fibers, since they are able to operate in the presence of an electron transport inhibitor.  Fast twitch fibers run anaerobically for the most part and do not carry out much aerobic respiration.  Nor do they have many mitochondria with which to perform aerobic respiration.

 

 

86) If fatty acids are a more efficient storehouse of energy than glucose or glycogen, why aren’t they used immediately to drive muscle contraction?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

Solution: While fatty acids store more energy per unit of mass, the lipids are more difficult to transport to the muscle than the glycogen, which is already there.  In addition, it takes longer to mobilize energy from fatty acids than from glycogen.

 

 

87) Which person would tend to have a higher proportion of slow-twitch than fast-twitch muscles: a weight lifter, a sprinter, or a long distance runner?

 

Answer:

 

Difficulty: Easy

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

Solution: The long distance runner will tend to have a higher proportion of slow twitch muscles.

 

 

88) Why do your muscles hurt for some time after a large amount of anaerobic exercise?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

Solution: If your muscles have been running anaerobically, they will produce lactic acid as a byproduct of fermentation.  The buildup of lactic acid can lower the pH of muscle tissue from 7.0 to 6.35.  This may lead to the pain and cramps that can accompany vigorous exercise.

 

 

89) What is meant by aerobic exercise?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

 

Solution: Aerobic exercises are designed to allow your muscles to continue to perform aerobically so that they can continue to make the necessary ATP by electron transport.  Such exercises depend largely upon the contraction of the slow-twitch fibers of the skeletal muscles.  They generate less force overall, but can continue to function for long periods of time due to their continuing aerobic production of ATP without the production of lactic acid.

 

 

90) Why is aerobic exercise one of the best ways to lose weight by decreasing the body’s fat content?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

Solution: Aerobic exercise is initially fueled by the glucose stored as glycogen in the muscles.  After a short time, however, the muscles depend increasingly on free fatty acids released into the bloodstream from adipose tissue.  As the exercise period increases in length, the dependency on fatty acids grows.  Within 20 minutes of vigorous aerobic exercise, it is estimated that about 50% of the calories consumed by muscles is derived from fat.  Thus, aerobic exercise is best at depleting the body’s fat stores.

 

 

91) Which muscles would contain more fast-twitch fibers, arm muscles or the postural muscles of the back?

 

Answer:

 

Difficulty: Easy

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

Solution: Arm muscles that are used to throw or lift an object, activities that require the generation of more force and thus a larger number of fast-twitch fibers, would have a higher proportion of fast-twitch fibers.

 

 

92) A muscle cell is obtained and studied with electron microscopy.  The study reveals that it has very few mitochondria.  What kind of muscle fiber is it?

 

Answer:

 

Difficulty: Hard

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

Solution: It is a fast-twitch fiber, since these fibers do relatively little aerobic respiration and thus have little need for many mitochondria.

 

 

93) Explain why fast-twitch fibers “prefer” to use anaerobic respiration rather than aerobic respiration even though aerobic respiration is about 20 times more efficient in terms of ATP produced per glucose molecule?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP

Solution: Glycolytic reactions occur much more rapidly than the reactions of the TCA cycle and electron transport.  Thus, while the yield of ATP is less efficient, the ATP that can be produced is produced at a higher rate. The higher rate of ATP production is better suited to the function and more forceful contractions of fast-twitch fibers.

 

 

94) Why does the DNA in mitochondria exhibit about 10 times the mutation rate seen in nuclear DNA and what is the possible effect of this on disease processes?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: Because of its proximity to electron-transport processes, which lead to the release of mutagenic oxygen radicals, mtDNA is thought to come under a much greater level of attack than nuclear DNA.  In addition, nuclear DNA is better protected from persistent damage by the presence of a greater variety of DNA repair systems.  Thus, damage inflicted upon nuclear DNA can be repaired, while damage to mitochondrial DNA cannot be repaired as effectively.  These factors explain the greater than 10-fold higher mutation rate of mtDNA.  Thus, mutations are particularly likely to accumulate in the mitochondria of cells that remain in the body for long periods of time (nerves and muscle tissue).  The degenerative changes in mitochondrial functions are thought to contribute to a number of common neurological diseases with adult-onset, most notably Parkinson’s disease (PD).

 

 

95) Which mitochondrial genes when mutated or experiencing deletions cause the most serious disorders?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: Mutations or deletions in the genes encoding the mitochondrial tRNAs tend to cause the most serious disorders.  Mitochondrial tRNAs are required for the synthesis of all 13 polypeptides produced in human mitochondria.

 

 

96) What is unique about the inheritance of mitochondrial disorders?  What word describes the mixture of wild-type and mutant mitochondrial DNA found in the mitochondria of a cell?

 

Answer:

 

Difficulty: Hard

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: They are not inherited in a Mendelian fashion, but exhibit maternal inheritance.  The mitochondria present in the cells of a human embryo are derived exclusively from mitochondria that were present in the egg at the time of conception without any contribution from the fertilizing sperm and thus they all come from the mother.  In addition, the mitochondria of a cell can contain a mixture of both normal (i.e., wild-type) and mutant mtDNA.  The level of mutant mtDNA can vary from one organ to another within a single individual, and it is only when a preponderance of the mitochondria in a particular tissue contains defective genetic information that clinical symptoms usually appear.  Because of this variability, members of a family carrying the same mtDNA mutation can exhibit significantly different symptoms.  Heteroplasmy describes the mixture of wild-type and mutant mitochondrial DNA found in the mitochondria of a cell.

 

 

97) A patient who has abnormal mitochondria has the following symptoms: long-term fatigue and muscle weakness, elevated metabolic rate and body temperature.  Studies indicate that the mitochondria have been released from their normal respiratory control.  How does this explain the elevated temperature?  Why are most disorders that have been traced to mitochondrial dysfunction characterized by degeneration of muscle or brain tissue?  What are the characteristics of some of the conditions that result from dysfunctional mitochondria?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: If the cells run at an abnormally high metabolic rate for a long time, energy given off that is not harnessed to do mechanical work will result in heat production instead, which will build up to higher levels than usual and thus increase body temperature.  Both of these tissues utilize exceptionally large amounts of ATP and thus degenerate because of the shortage of ATP that results from dysfunctional mitochondria.  These conditions range in severity from diseases that lead to death during infancy; to disorders that produce seizures, blindness, deafness, and/or stroke-like episodes; to mild conditions characterized by intolerance to exercise or nonmotile sperm.  Patients with serious conditions generally have abnormal skeletal muscle fibers, which contain large peripheral aggregates of mitochondria.  When examined, these mitochondria are seen to have large numbers of abnormal inclusions.

 

 

98) In the early 1980s, a number of young drug addicts showed up in hospitals with the sudden onset of severe muscular tremors that are characteristic of advanced Parkinson’s disease (PD) in elderly adults.  What caused these PD-like symptoms in such young people?  How were the cells of the substantia nigra in PD patients similar to those in the substantia nigra of MPTP patients?  What are some possible environmental causes of PD?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: They had intravenously injected themselves with a synthetic heroin that was contaminated with a compound called MPTP.  It was eventually discovered that MPTP caused damage to complex I of the mitochondrial respiratory chain, leading to the death of nerve cells in the same region of the brain (the substantia nigra) that is affected in PD patients.  Cells from the substantia nigra of PD patients were found to have a marked and selective decrease in complex I activity, just like the MPTP patients.  It appears that this complex I deficiency is probably due to a documented increase in the mutation rate in the DNA of these cells compared to other cells.  Exposure to certain pesticides, particularly rotenone, has been implicated as an environmental risk factor for PD development.  Rotenone is a known complex I inhibitor.  Administration of rotenone to rats causes the destruction of dopamine-producing neurons, which is characteristic of the human disease.

 

 

99) What happens to the mtDNA of mice that are homozygous for the mutant gene called Polg?  How do the “mutator” mice differ from their normal littermates?  How do mice that are heterozygous for the Polg mutation differ from those that are homozygous for the Polg mutation?  What should have happened to the life span of mice heterozygous for the Polg gene, if mtDNA mutations were a major contributor to the normal aging process?  What do the above results of studies of the Polg mutation suggest about the relationship between mtDNA mutations and premature aging in animals?

 

Answer:

 

Difficulty: Hard

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: The Polg gene encodes the enzyme that replicates mtDNA.  The mtDNA of these mutant mice (called “mutator” mice) accumulates a much higher level of mutations than that of their normal littermates.  The “mutator” mice appear normal for the first 6 to 9 months of age, but then rapidly develop signs of premature aging, such as hearing loss, graying hair and osteoporosis.  The control mice have a lifespan of more than two years, however, members of the experimental group live, on average, only about one year.  Mice heterozygous for the Polg mutation have an elevated mtDNA mutation rate (although far less than in the homozygotes).  They, however, do not exhibit a shortened life span.  If this were the case, the heterozygotes should have a significantly shorter life.  The results suggest mutations in mtDNA may be sufficient to cause an animal to age prematurely, but they are not necessarily required as part of the normal aging process.

 

 

100) What causes Zellweger’s syndrome?  What do the peroxisomes of ZS patients look like?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: Peroxisomes in Zellweger’s syndrome patients lack the peroxisomal enzymes that are normally found inside of them.  These enzymes are located in the cytoplasm instead.  It is caused by deficiencies in genes coding for receptor proteins that recognize peroxisomal enzymes or proteins that participate in the transport of peroxisomal enzymes across peroxisome membranes.  Genetic studies of cells from ZS patients showed that the disorder can arise from mutations in at least 12 different genes, all encoding proteins involved in the uptake of peroxisomal enzymes from the cytosol.  Initially, investigators thought that the peroxisomes were missing from the cells of these patients.  It was later found that peroxisomes were not entirely absent from the cells of these individuals.  Instead, they were present as empty membranous “ghosts”.  The organelles were present but the enzymes usually located within them were in the cytoplasm.

 

 

101) What is the basis of adrenoleukodystrophy (ALD) and other similar diseases?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: ALD and other similar diseases are caused by single enzyme/protein deficiencies in peroxisomes.  The missing enzyme/protein cannot oxidize its normal substrate, which then builds up to higher than normal levels.  These higher levels become toxic and damage tissues, eventually leading to debilitation or death.  In ALD, the defect is in a membrane protein that transports very-long-chain fatty acids (VLCFAs) into peroxisomes, where they are normally metabolized.  Without this protein, VLCFAs accumulate in the brain and destroy the myelin sheaths that insulate nerve cells.  Boys with this disease are usually unaffected until mid-childhood, when they begin to exhibit symptoms of adrenal insufficiency and neurological dysfunction.

 

 

102) What treatments have been tried to help ALD patients?

 

Answer:

 

Difficulty: Medium

Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.

Section Reference: Section 5.6 Peroxisomes

Solution: The movie Lorenzo’s Oil dealt with the parents of an ALD patient who discovered that a diet rich in certain fatty acids was able to retard the progress of the disease.  Subsequent studies have generated contradictory results regarding the value of this diet.  Some ALD patients have been helped by bone marrow transplantation, which provides normal cells capable of metabolizing VLCFAs and by administration of drugs (e.g., lovastatin) that may lower VLCFA levels.  Clinical studies employing gene therapy are also planned.

 

 

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