Principles of Human Physiology, 6th Edition Stanfield – Test Bank

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Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) In chemical communication between cells, a ________ cell secretes a chemical messenger that binds
to ________ on the ________ cell.
A) secretory : receptors : target
B) target : receptors : secretory
C) secretory : connexons : gap
D) gap : connexons : secretory
E) secretory : connexons : target
1)
2) Direct communication between cells in contact with one another is accomplished through
A) paracrine chemical messengers.
B) receptors.
C) ligands.
D) endocrine hormones.
E) gap junctions.
2)
3) The number of bound receptors on a target cell depends on what two things?
A) the secretory cell and target cell
B) the concentration of the messenger and signal transduction
C) the type and concentration of receptors
D) the concentration of the messenger and the distance it has to travel
E) the concentration of the messenger and the concentration of receptors on the target cell
3)
4) Which type of chemical messenger, when released, binds to receptors on the cell that released the
chemical messenger?
A) cytokine
B) autocrine
C) neurohormone
D) neurotransmitter
E) hormone
4)
5) Which type of chemical messenger is released into the bloodstream by an endocrine gland where it
can affect target cells throughout the body?
A) autocrine
B) cytokine
C) hormone
D) paracrine
E) neurotransmitter
5)
6) Which type of chemical messenger is released from the axon terminal of a neuron and directly
communicates with other cells?
A) hormone
B) cytokine
C) autocrine
D) neurotransmitter
E) paracrine
6)
1
7) Communication across a synapse is initiated by the release of a neurotransmitter from the ________
region of the neuron.
A) dendritic
B) postsynaptic
C) perisynaptic
D) axon hillock
E) axon terminal
7)
8) Vasopressin (antidiuretic hormone), which is released from the posterior pituitary, is an example of
what type of chemical messenger?
A) neurohormone
B) paracrine
C) autocrine
D) cytokine
E) neurotransmitter
8)
9) Inflammation is characterized in part by redness and swelling. In inflammation, ________ increases
blood flow to affected tissues (producing redness) and causes fluid to leak out of the blood vessels
and into the tissue (producing swelling).
A) clotting factor
B) pyruvic acid
C) amine
D) growth factor
E) histamine
9)
10) The more specific a drug is for a certain ________ type, the more specific the therapeutic actions of
the drug and the fewer the side effects.
A) ligand
B) target cell
C) receptor
D) neurotransmitter
E) hormone
10)
11) Which of the following chemical messengers is lipophilic and is therefore able to cross the cell
membrane?
A) eicosanoids
B) amines (excluding thyroid hormone)
C) proteins
D) amino acids
E) peptides
11)
12) Histamine acts as a(n) ________ in its role in inflammation.
A) autocrine
B) cytokine
C) hormone
D) neurotransmitter
E) paracrine
12)
2
13) What molecules are hydrophobic and can easily cross the plasma membrane?
A) lipophobic
B) lipophilic
C) hydrophilic
D) amino acids
E) hyperdermic
13)
14) All the messengers in what class are derived from cholesterol?
A) peptides/proteins
B) amino acids
C) steroids
D) amines
E) eicosanoids
14)
15) Most amines are ________, meaning they dissolve in water and therefore cannot cross the cell
membrane. The ________ hormones are an exception because they are ________ and can easily
cross the cell membrane.
A) amino acids : steroid : lipophilic
B) lipophilic : protein : lipophobic
C) hydrophobic : steroid : hydrophilic
D) lipophilic : thyroid : lipophobic
E) lipophobic : thyroid : lipophilic
15)
16) Peptide hormones are made________, stored and released via ________.
A) in advance : receptor-mediated endocytosis
B) on demand : simple diffusion
C) in advance : exocytosis
D) on demand : active transport
E) in advance : pinocytosis
16)
17) Cells that secrete dopamine must contain which enzymes?
A) tyrosine β-hydroxylase and dopa decarboxylase
B) dopa decarboxylase only
C) dopamine β-hydroxylase only
D) tyrosine β-hydroxylase
E) dopamine β-hydroxylase and dopa decarboxylase only
17)
18) Cells that secrete epinephrine must contain which enzymes?
A) dopamine β-hydroxylase, tyrosine β-hydroxylase, and dopa decarboxylase only
B) dopamine β-hydroxylase and dopa decarboxylase only
C) tyrosine β-hydroxylase and phenylethanolamine N-methyl transferase only
D) phenylethanolamine N-methyl transferase and dopa decarboxylase only
E) dopamine β-hydroxylase, tyrosine β-hydroxylase, phenylethanolamine N-methyl
transferase, and dopa decarboxylase
18)
19) Catecholamines are derived from what amino acid?
A) tryptophan
B) glutamate
C) tyrosine
D) glycine
E) histidine
19)
3
20) Thyroid hormones are synthesized from what amino acid?
A) tyrosine
B) glutamate
C) glycine
D) tryptophan
E) histidine
20)
21) Aspirin is a nonsteroidal anti-inflammatory drug (NSAID) that relieves pain. Which mechanism
best describes how NSAIDs work?
A) The COX receptors have a greater affinity for aspirin and these speed up the reactions of
healing.
B) Prostaglandins (PG) are eicosanoids that produce pain and inflammation. Cyclooxygenase
(COX) is an essential enzyme in the production of PG and aspirin inhibits COX and therefore
relieves pain due to the reduced production of PG.
C) Aspirin decreases the production of thromboxane A2, a chemical involved in blot clot
formation, and COX inhibits A2 and, therefore, blood clots do not form and cause pain.
D) When aspirin dissolves in the interstitial fluid it causes a concentration gradient and fluid is
pulled from the cell reducing inflammation.
E) Leukotrienes are eicosanoids that produce pain and inflammation. COX is used in the
lipoxygenase pathway and therefore NSAIDs stop the conversion of arachidonic acid to
leukotrienes thereby reducing inflammation.
21)
22) Doctors often prescribe baby aspirin (82 mg) to guard against the formation of blood clots instead
of a higher dose of 350 mg found in a regular aspirin. Which statement best describes the
distinction in dosages?
A) Low dosages of aspirin inhibit a critical enzyme in the production of prostaglandins called
cyclooxygenase (COX). There are two forms of COX: 1 and 2. Low dosages enhance the
production of COX-2 which reduces blood clots. COX-1 receptors only reduce pain.
B) Aspirin causes several side effects, some good and some bad. Aspirin decreases thromboxane
A2 which causes blood clots; however, at higher dosages, it also decreases the production of
PGI2 (prostacyclin) that inhibits production of blood clots. Thus, higher dosages of aspirin
would actually promote the formation of blood clots.
C) Aspirin is an allosteric modulator that activates COX-2 in the body and it is COX-2 that
primarily inhibits blood clot formation.
D) Aspirin inhibits the production of PGE2 in the stomach, which protects the stomach lining
from stomach acid causing ulcers. Lower dosages do not inhibit PGE2 and do not harm the
stomach.
E) Both dosages actually do the same thing to prevent blood clots but 82 mg of aspirin is much
cheaper than 350 mg.
22)
23) Once a steroid hormone is synthesized, it is
A) bound to albumin until released from the cell.
B) bound to the mitochondria until released.
C) stored in a unique protein structure that maintains steroids in the cell.
D) stored in a vesicle until released.
E) immediately capable of diffusing across the membrane.
23)
4
24) What organelle packages peptide/protein messengers into secretory vesicles?
A) rough endoplasmic reticulum
B) smooth endoplasmic reticulum
C) lysosomes
D) Golgi apparatus
E) nucleus
24)
25) In order to synthesize eicosanoids, ________ catalyzes the release of ________ from a membrane
phospholipid.
A) phospholipase C : inositol biphosphate
B) phospholipase A2 : cholesterol
C) phospholipase A2 : arachidonic acid
D) phospholipase C : cholesterol
E) phospholipase C : arachidonic acid
25)
26) An equilibrium exists between a hormone that is bound to a carrier protein and a free hormone
such that, as the amount of free hormone increases,
A) cells will be stimulated to secrete more free hormone.
B) more bound hormone will be released from its carrier proteins.
C) more free hormone will become bound to carrier proteins.
D) more hormone must be synthesized to directly replace the free hormones.
E) the amount of bound hormone will not change.
26)
27) Lipophilic chemical messengers are poorly soluble in water. However, many of these lipophilic
messengers are transported throughout the body. Their transport in blood (water) is facilitated by
A) chylomicrons.
B) red blood cells.
C) lipoproteins.
D) white blood cells.
E) carrier proteins.
27)
28) What enzyme catalyzes synthesis of prostaglandins from arachidonic acid?
A) tyrosine β-hydroxylase
B) phospholipase C
C) phospholipase A2
D) lipoxygenase
E) cyclooxygenase
28)
29) A half-life, in terms of a chemical messenger, refers to
A) the amount of time the messenger is bound to a protein.
B) the radioactivity of the chemical messenger.
C) how long the chemical messenger will be effective in the body.
D) the amount of time it takes to cross the plasma membrane.
E) the time it takes for half of the chemical messenger in the blood to be degraded.
29)
5
30) Androgens are precursor molecules for the synthesis of
A) progesterone.
B) cortisol.
C) cholesterol.
D) aldosterone.
E) estradiol.
30)
31) Progesterone is a potential precursor for the synthesis of
A) androstenedione.
B) cortisol.
C) dehydroepiandrosterone.
D) estradiol.
E) testosterone.
31)
32) Aspirin decreases inflammation by inhibiting the actions of what enzyme?
A) cyclooxygenase
B) lipoxygenase
C) protein kinase A
D) phospholipase A2
E) dopa decarboxylase
32)
33) Hormones that are dissolved in blood typically exhibit a half-life on the order of ________, whereas
hormones that are bound to carrier proteins can remain undegraded for ________.
A) seconds : hours
B) minutes : hours
C) seconds : minutes
D) minutes : seconds
E) hours : minutes
33)
34) The location of receptors on a target cell depends on the solubility of the chemical messenger.
Where would the receptors for lipophilic messengers be located?
A) on the outside of the cell
B) only in the nucleus of the cell
C) at a free floating ribosome
D) on the inside of the cell
E) It depends on if it is an alpha, beta, or delta type receptor.
34)
35) The β1 adrenergic receptor has the greatest affinity for what messenger?
A) serotonin
B) epinephrine
C) dopamine
D) norepinephrine
E) epinephrine and norepinephrine equally
35)
36) The α1 adrenergic receptor has the greatest affinity for what messenger?
A) dopamine
B) serotonin
C) epinephrine
D) norepinephrine
E) epinephrine and norepinephrine equally
36)
6
37) Which of the following will NOT affect the magnitude of a cell’s response to a specific hydrophilic
ligand?
A) lipid solubility of the ligand
B) number of receptors
C) affinity of the receptor for the ligand
D) receptor upregulation
E) ligand concentration
37)
38) Chronic exposure to a ligand (messenger) ________ the receptor population for that chemical
messenger on the target cell.
A) decreases the affinity of
B) changes the conformation of
C) decreases the specificity of
D) down regulates
E) upregulates
38)
39) Which of the following statements best describes the release of lipophobic messengers?
A) Lipophobic messengers are stored free in the cytosol and released by simple diffusion in
response to a stimulus.
B) Lipophobic messengers are stored in vesicles and released by exocytosis in response to a
stimulus.
C) Lipophobic messengers are stored in vesicles and released by simple diffusion in response to
a stimulus.
D) Lipophobic messengers are released immediately upon synthesis by simple diffusion.
E) Lipophobic messengers are stored in vesicles and released by exocytosis immediately after
synthesis.
39)
40) Which of the following statements best describes the release of a lipophilic messenger?
A) Lipophilic messengers are stored in vesicles and released by simple diffusion in response to a
stimulus.
B) Lipophilic messengers are released immediately upon synthesis by simple diffusion.
C) Lipophilic messengers are stored in vesicles and released by exocytosis in response to a
stimulus.
D) Lipophilic messengers are stored free in the cytosol and released by simple diffusion in
response to a stimulus.
E) Lipophilic messengers are stored in vesicles and released by exocytosis immediately after
synthesis.
40)
41) Lipophilic hormones are transported in blood ________ and bind to receptors located ________.
A) bound to carrier proteins : inside the target cell
B) dissolved in the plasma : on the plasma membrane of the target cell
C) inside red blood cells : inside the target cell
D) dissolved in the plasma : inside the target cell
E) bound to carrier proteins : on the plasma membrane of the target cell
41)
7
42) Much evidence suggests that depression might be associated with deficiencies in the biogenic
amines serotonin and norepinephrine. If this is true and the body has reduced concentrations of
these amines, one might predict the body would ________ in order to adapt to these lowered levels.
A) downregulate
B) increase the half life
C) upregulate
D) increase the concentration of chemical messenger
E) reduce the affinity
42)
43) What is a molecule that is similar in structure to a messenger and binds with that messenger’s
receptor to stimulate a similar response from the target cell?
A) protagonist
B) synergist
C) blocker
D) agonist
E) antagonist
43)
44) As a general rule, the magnitude of a target cell’s response to a chemical messenger depends on
which three factors?
A) (1) the half life of the messenger, (2) the number of receptors, and (3) the percent saturation of
those receptors
B) (1) the solubility of the chemical messenger, (2) the location of the receptor, and (3) the affinity
of the receptor to the messenger
C) (1) the solubility of the chemical messenger, (2) the location of the receptor, and (3) the class of
the receptor
D) (1) the concentration of the messenger, (2) the number of receptors, and (3) the affinity of the
receptor for the messenger
E) (1) the concentration of the messenger, (2) the percent saturation of the receptor, and (3) the
specificity of the receptor for the chemical messenger
44)
45) The affinity of a receptor for its ligand is a measure of the
A) response produced in the target cell when the ligand binds to the receptor.
B) number of binding sites available for the ligand.
C) strength of binding between ligand and receptor.
D) ability of the ligand to permeate the plasma membrane and reach its receptor.
E) percent of receptors on a specific target cell with bound ligand.
45)
46) Typical responses to ________ messengers require a long time to develop because they necessitate
transcription of mRNA and translation of that mRNA into a functional protein.
A) protein
B) lipophilic
C) lipophobic
D) peptide
E) amino acid
46)
8
47) Insulin is a peptide hormone and therefore lipophobic. When insulin is released due to high blood
glucose levels, the response of the cells to this hormone will be ________ because it causes
________.
A) fast : enzyme-linked receptors to catalyze intracellular reactions
B) fast : new protein synthesis
C) slow : amplification of proteins
D) neutral : transcription of mRNA and translation of that mRNA into a functional protein
E) slow : a second messenger system to be activated
47)
48) Heroin overdose is usually treated with an opioid ________ such as naloxone (Narcan) or
naltrexone, an opioid, which prevents heroin from binding to mu receptors and reverses the effects
of heroin on the body.
A) ligand
B) second messenger
C) antagonist
D) agonist
E) antihistamine
48)
49) Differences in the rate of activity between fast and slow ligand-gated channels are caused by
A) G protein activity gating the slow channel.
B) G protein activity gating the fast channel.
C) ligand selectivity.
D) ligands gating both channels to the closed state.
E) ligand affinity.
49)
50) Opening channels for which of the following ions can trigger exocytosis?
A) potassium
B) chloride
C) calcium
D) magnesium
E) sodium
50)
51) Which of the following ions binds to calmodulin to ultimately activate a protein kinase?
A) calcium
B) potassium
C) magnesium
D) sodium
E) chloride
51)
52) A first messenger is an extracellular messenger that binds to its receptor on the ________ of the cell
and therefore activates a second messenger system.
A) ribosome
B) inside
C) endoplasmic reticulum
D) G protein
E) outside
52)
9
53) Which of the following statements best describes the function of tyrosine kinase?
A) It catalyzes the formation of dopamine from L-dopa.
B) It catalyzes the phosphorylation of a protein inside a cell.
C) It sequesters calcium in the cytosol.
D) It catalyzes the phosphorylation of a protein in the extracellular fluid.
E) It catalyzes the formation of norepinephrine from dopamine.
53)
54) Cholera is the leading cause of death in children in developing countries, characterized by massive
diarrhea. The effects stem from an extracellular toxin that the bacterium Vibrio cholerae releases
into the gut. The toxin acts on a ________ that overstimulates ________ which causes a cascade of
events that leads to electrolytes leaving the cell and causing water to follow them into the lumen of
the intestine, resulting in severe diarrhea.
A) protein kinases : calmodulin
B) G proteins : adenylate cyclase
C) cAMP : G proteins
D) calcium : muscles
E) protein-P : GTP
54)
55) Which of the following is the most common second messenger in the human body?
A) cAMP B) IP3 C) DAG D) calcium E) cGMP
55)
56) What terminates the cAMP second messenger system?
A) degradation of cAMP by the liver
B) the release of the first messenger from the receptor
C) the degradation of cAMP by the enzyme cAMP phosphodiesterase
D) a G protein
E) the axon terminal
56)
57) Cyclic AMP (cAMP) stimulates one’s metabolic rate. Many supplement companies offer products
claiming to increase the levels of this chemical within the body. If you had a patient on this
supplement and they had high levels of cAMP in their body, what symptoms would you expect
them to display?
A) hypoglycemia and low blood pressure
B) increased heart rate and shallow breathing
C) weight gain and lethargy
D) weight loss and a high temperature
E) high G protein and sugar levels in their urine
57)
58) The function of a second messenger system is to
A) isolate the response to the inside of a cell.
B) amplify the response of the first messenger.
C) facilitate the process of covalent modification of a protein.
D) keep calcium involved in these responses.
E) buffer a cell’s response to a ligand.
58)
10
59) Based on your knowledge of signal amplification, which type of chemical messenger can have
relatively small concentrations within the bloodstream and still get a large response?
A) lipophilic
B) lipophobic
C) steroid
D) paracrine
E) autocrine
59)
60) Functionally, G proteins are classified into what three types?
A) alpha, beta, and gamma
B) slow, fast, and opened or closed
C) first, second, and third messengers
D) those that affect ion channels, stimulatory G proteins, and inhibitory G proteins
E) those that affect proteins, those that affect enzymes, and those that affect specific genes
60)
61) When the alpha subunit of the G protein is activated, it can stimulate ion channels to do what?
A) either open or close
B) alter the ion that travels through the channel
C) close only
D) open only
E) degrade
61)
62) The enzyme that catalyzes synthesis of cAMP is called ________ and is activated by ________.
A) adenylate cyclase : a Gs protein
B) phosphodiesterase : a Gs protein
C) phosphodiesterase : a Gi protein
D) adenylate cyclase : a Gi protein
E) phosphoprotein phosphatase : a Gi protein
62)
63) What enzyme is activated by cAMP?
A) phosphodiesterase
B) protein kinase A
C) protein kinase C
D) adenylate cyclase
E) tyrosine kinase
63)
64) In order to terminate a cAMP-mediated response, the enzyme ________ can be activated to
degrade cAMP.
A) cAMP hydrolase
B) cAMP phosphodiesterase
C) cAMP protein kinase
D) cAMP decarboxylase
E) cAMP hydrogenase
64)
65) When associated with G protein, guanylate cyclase will activate what enzyme?
A) protein kinase C
B) phosphodiesterase
C) phospholipase C
D) protein kinase A
E) protein kinase G
65)
11
66) What molecule, whose synthesis is catalyzed by phospholipase C, triggers the release of calcium
from the endoplasmic reticulum?
A) phosphatidylinositol biphosphate
B) cGMP
C) inositol biphosphate
D) diacylglycerol
E) inositol triphosphate
66)
67) Which of the following proteins is directly activated by a G protein?
A) tyrosine kinase
B) calmodulin
C) phospholipase A2
D) adenylate cyclase
E) protein kinase G
67)
68) Which of the following are second messengers?
A) cAMP only
B) calcium only
C) inositol triphosphate only
D) both cAMP and inositol triphosphate
E) cAMP, calcium, and inositol triphosphate
68)
69) What two systems primarily control homeostasis due to their ability to communicate over long
distances?
A) nervous and cardiovascular
B) endocrine and cardiovascular
C) cardiovascular and respiratory
D) endocrine and respiratory
E) nervous and endocrine
69)
70) The chemical messenger of the nervous system is ________ and chemical messenger of the
endocrine system is ________.
A) neurotransmitter : hormone
B) neurohormone : adrenocorticoid
C) autocrines : paracrines
D) hormone : neurotransmitter
E) neurotransmitter : neurohormone
70)
71) The target cells of the nervous system are
A) all the cell types in the body.
B) other neurons.
C) muscle cells.
D) glial cells.
E) neurons, muscles, or glands.
71)
12
72) The nervous system communicates via the ________ and the endocrine system communicates via
the ________.
A) synapse : bloodstream
B) neuron : endocrine gland
C) glial cell : hormone
D) electrical signals : chemical signals or paracrine cells
E) muscle cells : specific target cells of hormones
72)
73) Which of the following statements is true for the nervous system but NOT the endocrine system?
A) A messenger communicates to target cells by binding to specific receptors.
B) There is a special anatomical arrangement between the secretory cell and the target cell.
C) Communication occurs over long distances.
D) A messenger is transported in the bloodstream.
E) Effector organs are scattered throughout the body.
73)
74) What part of a neuron releases neurotransmitter by exocytosis?
A) dendrites
B) axon hillock
C) axon terminal
D) soma
E) All of the answers are correct.
74)
75) What chemical messenger diffuses to neighboring cells to exert an effect?
A) paracrine
B) neurohormone
C) hormone
D) neurotransmitter
E) autocrine
75)
76) What chemical messenger is released from endocrine glands into the bloodstream?
A) autocrine
B) paracrine
C) neurohormone
D) hormone
E) neurotransmitter
76)
77) What chemical messenger is released by a presynaptic cell?
A) hormone
B) neurotransmitter
C) neurohormone
D) autocrine
E) paracrine
77)
78) Which of the following enzymes catalyzes phosphorylation of a protein?
A) phospholipase A2
B) adenylate cyclase
C) tyrosine kinase
D) phosphodiesterase
E) tyrosine β-hydroxylase
78)
13
79) Which of the following enzymes catalyzes synthesis and release of arachidonic acid?
A) adenylate cyclase
B) tyrosine kinase
C) tyrosine β-hydroxylase
D) phosphodiesterase
E) phospholipase A2
79)
80) Which of the following enzymes catalyzes synthesis of epinephrine from norepinephrine?
A) dopa decarboxylase
B) phenylethanolamine N-methyl transferase
C) phospholipase C
D) phosphoprotein phosphatase
E) dopamine β-hydroxylase
80)
81) Which of the following enzymes catalyzes synthesis of cAMP?
A) adenylate cyclase
B) tyrosine kinase
C) phosphodiesterase
D) phospholipase A2
E) tyrosine β-hydroxylase
81)
82) Which of the following enzymes catalyzes synthesis of prostaglandins and thromboxanes?
A) phenylethanolamine N-methyl transferase
B) phospholipase C
C) dopamine β-hydroxylase
D) phosphoprotein phosphatase
E) cyclooxygenase
82)
83) Which of the following enzymes catalyzes dephosphorylation of a protein?
A) phenylethanolamine N-methyl transferase
B) phosphoprotein phosphatase
C) cyclooxygenase
D) dopamine β-hydroxylase
E) phospholipase C
83)
84) Which of the following enzymes catalyzes synthesis of diacylglycerol and inositol triphosphate?
A) phenylethanolamine N-methyl transferase
B) cyclooxygenase
C) phosphoprotein phosphatase
D) phospholipase C
E) dopamine β-hydroxylase
84)
85) A target cell will respond to a chemical messenger once that molecule has bound to a
A) receptor.
B) G protein.
C) calcium channel.
D) complex in the nucleus.
E) protein kinase.
85)
14
86) A(n) ________ is transported in the bloodstream.
A) neurotransmitter
B) paracrine
C) autocrine
D) glial cell
E) hormone
86)
87) Histamine is an example of a(n)
A) paracrine.
B) hormone.
C) neurotransmitter.
D) autocrine.
E) glial cell.
87)
88) Lipid-soluble molecules are not only hydrophobic, but are also
A) disaccharides.
B) lipophobic.
C) amino acids.
D) lipophilic.
E) cellulose.
88)
89) Catecholamines, such as dopamine, norepinephrine, and epinephrine, are derived from the amino
acid
A) glutamate. B) tyrosine. C) leucine. D) isoleucine. E) glycine.
89)
90) Identify the two enzymes involved in converting tyrosine into dopamine.
A) dopamine β-hydroxylase and propeptide
B) andenylate cyclase and phospholipase C
C) tyrosine β hydroxylase and dopa decarboxylase
D) cortisol and dehydroepiandrosterone
E) cyclooxygenase and lipoxygenase
90)
91) Eicosanoids are derived from what phospholipid?
A) prostacycline
B) arachidonic acid
C) prostoglandins
D) thromboxanes
E) leukotrienes
91)
92) Steroid messengers are derived from what precursor molecule?
A) calmodulin
B) arachidonic acid
C) cholesterol
D) tyrosine
E) histamine
92)
15
93) Catecholamines are released from the secretory cell by
A) endocytosis.
B) signal transduction.
C) exocytosis.
D) simple diffusion.
E) active transport.
93)
94) Steroids are released from the secretory cell by
A) endocytosis.
B) simple diffusion.
C) exocytosis.
D) signal transduction.
E) active transport.
94)
95) What protein in the blood that is relatively non-specific with respect to its ability to bind and
transport chemical messengers in the blood?
A) hemoglobin
B) albumin
C) protein kinase
D) cytokine
E) corticosteroid-binding globulin
95)
96) As free hormones bind to their receptors and no more hormone is released from their cell of origin,
the concentration of hormone bound to carrier proteins will
A) have a greater affinity.
B) decrease.
C) denature.
D) increase.
E) become saturated.
96)
97) The strength with which a ligand (chemical messenger) will bind with a receptor is referred to as its
A) enzyme-substrate complex.
B) affinity.
C) binding strength.
D) prohormone.
E) prepropeptide.
97)
98) As the concentration of receptors on the cell membrane decreases, the response of the target cell
will
A) increase its affinity.
B) increase.
C) decrease.
D) remain the same due to saturation.
E) oscillate with the concentration of the chemical messenger.
98)
99) Which of the following chemical messengers are lipophilic?
A) eicosanoids
B) steroids
C) thyroid hormones
D) peptides/proteins
E) steroids, eicosanoids, and thyroid hormone
99)
16
100) Which of the following chemical messengers are lipophobic?
A) thyroid hormones
B) peptides/proteins and steroids
C) steroids
D) peptides/proteins
E) amino acids
100)
TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
101) Lipophobic chemical messengers communicate a message to the target cell by binding to receptors
on that cell’s membrane.
101)
102) The target cell of a neurotransmitter is the postsynaptic cell. 102)
103) Endocrine glands secrete neurohormones. 103)
104) Tyrosine is one of four amino acids that function directly as chemical messengers. 104)
105) Steroid hormones are produced within cells and stored in vesicles until they are released. 105)
106) Steroid hormones are derived from the hormone testosterone. 106)
107) All catecholamine-secreting cells synthesize dopamine. 107)
108) Eicosanoids are released immediately upon synthesis. 108)
109) The location of the receptor depends on whether the messenger is lipophilic or lipophobic. 109)
110) A single cell can have receptors for different messengers. 110)
111) Most receptors are relatively non-specific for the ligand that will bind to them. 111)
112) Receptors for lipophilic chemical messengers are only located on the surface of a cell’s membrane. 112)
113) Tyrosine kinases are enzymes that add a phosphate group to tyrosine residues on other proteins,
changing the conformation of those proteins.
113)
114) The higher concentration of messenger, the greater the response in the target cell. 114)
115) Enkephalin is an opiate produced in the body. When enkephalin binds to opioid receptors, it
produces analgesia (a lack of pain sensation). Morphine can also bind to opioid receptors and
produce analgesia. Morphine is an opiate antagonist.
115)
116) Thyroid hormones alter the transcription of mRNA in the target cell. 116)
117) If calcium channels open in the plasma membrane, calcium ions enter the cell. 117)
118) An amplifier enzyme catalyzes the synthesis of a second messenger. 118)
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119) In its active form, a G protein has a GDP bound to its alpha unit. 119)
120) Generally, the nervous system is a more rapid means of communication than the endocrine system. 120)
121) The site of communication between two neurons is called a synapse. 121)
ESSAY. Write your answer in the space provided or on a separate sheet of paper.
122) Compare and contrast the synthesis, release, transport, and signal transduction of lipophilic and lipophobic
chemical messengers.
123) Aspirin, also known as acetylsalicylic acid, is one of the most widely used medications in the world. To what
group of medications does aspirin belong? Explain its mechanism of action for preventing pain and
inflammation as well as its ability to prevent blood clots. Aspirin also has some undesirable side effects,
especially in higher doses. Explain what these side effects are and why they occur.
124) Describe the factors that affect the magnitude of a target cell’s response. Assume that there is a receptor on the
cell for the ligand.
125) Describe the function of both slow and fast channel-linked receptors. Include the role of calcium as a second
messenger.
126) Describe G protein-linked receptors, including a discussion of the different enzyme pathways activated by G
protein.
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Answer Key
Testname: UNTITLED1
1) A
2) E
3) E
4) B
5) C
6) D
7) E
8) A
9) E
10) C
11) A
12) E
13) B
14) C
15) E
16) C
17) A
18) E
19) C
20) A
21) B
22) B
23) E
24) D
25) C
26) C
27) E
28) E
29) E
30) E
31) B
32) A
33) B
34) D
35) E
36) D
37) A
38) D
39) B
40) B
41) A
42) C
43) D
44) D
45) C
46) B
47) A
48) C
49) A
50) C
19
Answer Key
Testname: UNTITLED1
51) A
52) E
53) B
54) B
55) A
56) C
57) D
58) B
59) B
60) D
61) A
62) A
63) B
64) B
65) E
66) E
67) D
68) E
69) E
70) A
71) E
72) A
73) B
74) C
75) A
76) D
77) B
78) C
79) E
80) B
81) A
82) E
83) B
84) D
85) A
86) E
87) A
88) D
89) B
90) C
91) B
92) C
93) C
94) B
95) B
96) B
97) B
98) C
99) E
100) E
20
Answer Key
Testname: UNTITLED1
101) TRUE
102) TRUE
103) FALSE
104) FALSE
105) FALSE
106) FALSE
107) TRUE
108) TRUE
109) TRUE
110) TRUE
111) FALSE
112) FALSE
113) TRUE
114) TRUE
115) FALSE
116) TRUE
117) TRUE
118) TRUE
119) FALSE
120) TRUE
121) TRUE
122) Lipophilic (hydrophobic) messengers include the steroids, eicosanoids, and thyroid hormones. They are secreted via
simple diffusion from the cell that secretes them and must be bound to a carrier protein in the bloodstream. The
location of the receptor on their target cell is either in the nucleus or cytosol and their action on the target cell requires
the synthesis of a new protein. Due to this new protein synthesis, these chemical messengers have a relatively slow
response time but a long duration and a long have life in the body.
In contrast, lipophobic (hydrophilic) messengers include those chemical messenger classes of amino acids, amines, and
peptides. They are usually made in advance via protein synthesis, stored in secretory vesicles, and released into the
bloodstream via exocytosis where they dissolve into the plasma. Since they are lipophobic, the receptor on their target
cell is located on the outside of the cell and, therefore, once they bind to the receptor, they activate a second messenger
system within the cell which has a fast response time due to the amplification of activated enzymes within the cell.
Lipophobic messengers have a short half-life and a short duration of response.
123) Aspirin is one of a number of nonsteroidal anti-inflammatory drugs (NSAIDs). Their mechanism of action is to target
the enzyme cyclooxygenase (COX), which has two forms COX-1 and COX-2. COX is a critical enzyme in the synthesis
of prostaglandins (PG), eicosanoids that cause pain and inflammation. COX-1 is present in many cells of the body and
helps maintain homeostasis and synthesizes PG. Aspirin, however, nonselectively inhibits both forms of the COX
enzyme but it is the inhibition of COX-2 that results in pain relief.
Several side effects occur when aspirin inhibits the COX-1 enzyme because aspirin decreases the production of
thromboxane A2, a chemical that is involved in the formation of blood clots.
However, at higher doses, aspirin also decreases the production of PGI2 (prostacyclin), a chemical that inhibits the
production of blood clots. Therefore, a lower dose of 82 mg (a baby aspirin) will decrease the production of
thromboxane A2 causing a beneficial side effect of taking aspirin. In larger dosages (like those found in regular
aspirin), although they will reduce pain and inflammation, they will also actually promote the formation of blood clots
due to decreasing the production of PGI2. Another undesirable side effect of aspirin is the formation of ulcers and
stomach bleeding and upset because aspirin also inhibits the production of PGE2 which indirectly protects the lining of
the stomach from stomach acid.
21
Answer Key
Testname: UNTITLED1
124) The first factor that affects a target cell’s response to a ligand is the concentration of the ligand. The kinetics of a
ligand’s binding to a receptor is shown as M + R ⇌ M*R → Response, where M is the messenger (ligand), R is the
receptor, and M*R is the messenger-receptor complex. As the concentration of ligand increases, the number of bound
receptors will increase until all receptors on the target cell are bound by ligand (saturated). This relationship between
ligand and receptor means that the response to a ligand will also be affected by the number of receptors available. At
any concentration of ligand, the number of receptors bound depends upon the total number of receptors on the target
cell. In order to change the number of receptors on the target cell, some time is required to alter the regulation of
protein synthesis or degradation of that receptor. If the concentration of ligand is low for long periods of time, cells
tend to upregulate (increase) the number of receptors for that ligand. In that way, the cell can be more responsive to
lower concentrations of ligand. Alternatively, long periods of high ligand concentration may downregulate that
ligand’s receptor population, thereby reducing the cell’s responsiveness to the ligand. Finally, a cell’s responsiveness to
a ligand is determined by the affinity of the receptor for the ligand. As the receptor affinity increases, more receptors
will be bound at the same ligand concentration. This is especially important when there are several classes of receptors
that have different affinities for a ligand such as epinephrine. Two types of receptors are capable of binding the
catecholamine epinephrine: α and β2 adrenergic receptors. Both of these receptors are found on blood vessels and have
the opposite effect on those vessels: α adrenoreceptors induce vasoconstriction, whereas β2 adrenoreceptors induce
vasodilation. However, in the presence of epinephrine, the β2 adrenoreceptor-induced vasodilation will predominate
because the β2 adrenoreceptor has a greater affinity for epinephrine than the α adrenoreceptor.
125) Channel-linked receptors function in the gating of an ion channel into the open or closed states in response to
ligand-receptor binding. These ligand-gated channels are usually very specific for a particular ion and fall into two
categories: fast and slow channels. Fast channels are those where the receptor and channel are directly coupled. With
slow channels, the receptor and channel are linked by confusing a G protein. The binding of a ligand to a fast channel
receptor will increase the likelihood that an ion channel will open. That channel will only remain open for a short
period of time, allowing the flux of a particular ion across the membrane either into or out of the cell, depending upon
that ion’s electrochemical gradient. The flux of ions across a membrane can alter cellular function in two ways: by
changing that cell’s membrane potential, and/or the ion can act as a second messenger inside the cell. The movement of
sodium into a cell induces a rapid depolarization. Alternatively, if the channel is specific for calcium, then the influx of
calcium can trigger a series of responses by binding to the cytosolic protein calmodulin or by binding to other proteins.
The calcium-calmodulin complex activates a protein kinase which catalyzes phosphorylation of a protein. Calcium is
well suited to this role due to its low cytosolic concentration, making the cell very responsive to changes in intracellular
calcium. The cytosolic concentration of calcium is kept low by: 1) the active transport of calcium out of the cell; 2)
sequestration of calcium by cytosolic binding proteins; and 3) the active transport of calcium into the smooth
endoplasmic reticulum and mitochondria.
22
Answer Key
Testname: UNTITLED1
126) G proteins act as a bridge between a receptor and a channel. Receptor-ligand binding activates a G protein within the
cell membrane. G proteins can act through a number of second messenger pathways. cAMP is the most common
pathway. A ligand binding to its receptor will activate Gs (or Gi, depending upon the receptor). The α subunit of the G
protein is released to activate the enzyme adenylate cyclase. This step appears to be the most important because
several other enzymes can be activated by the α subunit of the G protein. Adenylate cyclase catalyzes the conversion of
ATP to cAMP. Once produced, cAMP will activate protein kinase A (cAMP-dependent protein kinase) by
phosphorylating it. Protein kinase A uses ATP to phosphorylate another enzyme, thereby altering that protein’s
function and causing a response within the cell. This cascade of reactions can be halted by the action of the cAMP
phosphodiesterase, which degrades cAMP. At the same time, the protein activated by protein kinase A can be
inactivated by a phosphatase enzyme that removes the phosphate group. As stated above, the α subunit of G protein
could activate other enzymes like guanylate cyclase, which would stimulate the production of cGMP and ultimately
activate protein kinase G. In addition, the α subunit of G protein could activate the enzyme phospholipase C. This
enzyme is part of the phosphatidylinositol system. Activation of phospholipase C cleaves the membrane phospholipid
phosphatidylinositol 4,5-biphosphate (PIP2) into diacylglycerol (DAG) and inositol triphosphate (IP3). DAG remains
in the membrane and activates protein kinase C, which stimulates other enzymes to initiate a cellular response. IP3
moves into the cytosol and stimulates the release of calcium from the endoplasmic reticulum. In this case, it is calcium
that stimulates the cellular response through its binding to calmodulin or another protein with a calcium binding site.
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