Biochemistry A Short Course First Edition by John L. Tymoczko – Test Bank

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Chapter 5   Techniques in Protein Biochemistry

 

 

Matching Questions

Use the following to answer questions 1-10:

 

Choose the correct answer from the list below. Not all of the answers will be used.

  1. a) HPLC
  2. b) specific activity
  3. c) MALDI-TOF mass spectrum
  4. d) gradient centrifugation
  5. e) proteome
  6. f) SDS
  7. g) two-dimensional electrophoresis
  8. h) Svedberg
  9. i) immunoglobulin
  10. j) differential centrifugation
  11. k) overlap peptides
  12. l) affinity chromatography

 

1. The ratio of enzyme activity relative to total protein is called ____________.

 

  Ans: b
  Section:  5.2

 

2. The first step in protein purification from a homogenate is usually ____________.

 

  Ans: j
  Section:  5.2

 

3. ____________ A type of purification that is based on the attraction of the protein for a particular chemical group.

 

  Ans: l
  Section:  5.2

 

4. ____________ can be added prior to gel electrophoresis to denature the proteins.

 

  Ans: f
  Section:  5.2

 

5. Sedimentation coefficients are expressed in ____________ units.

 

  Ans: h
  Section:  5.3

 

6. Proteins with different sedimentation coefficients can be separated by ____________.

 

  Ans: d
  Section:  5.3

 

7. In order to sequence a whole protein, ____________ are used.

 

  Ans: k
  Section:  5.4

 

8. ____________ The subset of gene products actually expressed by the cell.

 

  Ans: e
  Section:  5.1

 

9. ____________ A protein purification technique characterized by high resolution and rapid separation.

 

  Ans: j
  Section:  5.2

 

10. ____________ The separation of proteins based on charge then size.

 

  Ans: g
  Section:  5.2

 

 

Fill-in-the Blank Questions

 

11. Proteins can be separated from small molecules and ions through a semi-permeable membrane by      .
  Ans:  dialysis     Section:  5.2

 

12. Molecular exclusion gel or gel-filtration chromatography separates molecules on the basis of     .                        
  Ans:  size     Section:  5.2

 

13.  In amino acid composition analysis, amino acids are visualized after separation using the chemical reagent      .
  Ans:  fluorescamine     Section:  5.4

 

14. In the Edman procedure for peptide sequence, phenyl isothiocyanate is used to selectively remove the       residue as a PTH-derivative.
  Ans:  amino-terminal     Section:  5.4

 

15. Antibodies used as reagents to quantify proteins or other antigens is the basis for the technique called      .
  Ans:  ELISA (enzyme-linked immunosorbent assay)     Section:  5.3

 

 

16.       allows the detection of small amounts and the size of target proteins.
  Ans:  Western blotting or immunoblotting     Section:  5.3

 

17. Polypeptides can be fragmented into smaller peptides by cleavage with chymotrypsin, which hydrolyzes the peptide bond at the C-terminal side of      residues.
  Ans:  phenyalanine, tyrosine, and tryptophan     Section:  5.4

 

18.       gels are often used as the media for electrophoretic techniques such as SDS-PAGE and isoelectric focusing.
  Ans:  Polyacrylamide     Section:  5.4

 

19. The      of a protein is the pH at which its net charge is zero.
  Ans:  isoelectric point     Section:  5.2

 

 

Multiple-Choice Questions

 

20. When enzymes are purified, the assay is often based on:
  A) light absorbance. D) temperature changes.
  B) catalytic activity. E) mRNA levels.
  C) pH.    
  Ans:  B     Section:  5.2

 

21. Receptor proteins are often assayed using:
  A) binding assays. D) None of the above.
  B) enzymatic activity. E) All of the above.
  C) amino acid analysis.    
  Ans:  A     Section:  5.3

 

22. What is the advantage of adding SDS to gel electrophoresis?
  A) SDS colors the proteins for visualization.
  B) SDS reduces disulfide bonds.
  C) SDS allows proteins to be separated on the basis of approximate mass.
  D) None of the above.
  E) All of the above.
  Ans:  C     Section:  5.2

 

23. Two-dimensional electrophoresis is a combination of what two techniques?
  A) isoelectric focusing and affinity chromatography
  B) ion-exchange chromatography and SDS-PAGE
  C) affinity chromatography and SDS-PAGE
  D) isoelectric focusing and SDS-PAGE
  E) isoelectric focusing and ion-exchange chromatography
  Ans:  D     Section:  5.2

 

 

24. Which of the following affects the sedimentation of a particle?
  A) mass D) All of the above.
  B) shape E) A and B
  C) the density of the solution    
  Ans:  D     Section:  5.3

 

25. Cyanogen bromide cleaves the peptide bond at:
  A) the carboxyl side of Arg and Lys residues.
  B) the carboxyl side of Met residues.
  C) the amino terminus.
  D) None of the above.
  E) All of the above.
  Ans:  B     Section:  5.4

 

26. Trypsin cleaves the peptide bond at:
  A) the carboxyl side of Arg and Lys residues.
  B) the carboxyl side of Met residues.
  C) the amino terminus.
  D) None of the above.
  E) All of the above.
  Ans:  A     Section:  5.4

 

27. Which of the following techniques can be used to determine the size of a target protein?
  A) Edman degradation D) ELISA
  B) affinity chromatography E) isoelectric focusing gel
  C) western blot    
  Ans:  C     Section:  5.3

 

28. What types of molecules can serve as antigens?
  A) proteins D) All of the above.
  B) polysaccharides E) A and B
  C) metal ions    
  Ans:  E     Section:  5.3

 

29. Affinity chromatographs:
  A) allow high resolution and rapid separation. D) separate proteins based on attraction to another molecule.
  B) separate proteins based on size. E) separate proteins based on charge and size.
  C) separate proteins based on charge.    
  Ans:  D     Section:  5.2

 

30. What conditions could cause changes in the proteome of a cell?
  A) developmental stage
  B) environmental condition
  C) enzymatic modification
  D) All of the above.
  E) None of the above.
  Ans:  D     Section:  5.1

 

31. Which technique cannot be used for quantitative analysis?
  A) gradient centrifugation D) All of the above.
  B) ELISA E) None of the above.
  C) enzyme assay    
  Ans:  A     Section:  Entire Chapter

 

32. Which of the following is true regarding gel filtration chromatography and PAGE?
  A) In both, small proteins move most rapidly. D) In gel filtration, large proteins move most rapidly, but in PAGE, small proteins move most rapidly.
  B) In both, large proteins move most rapidly. E) None of the above.
  C) In PAGE, large proteins move most rapidly but in gel filtration, small proteins move most rapidly.    
  Ans:  D     Section:  5.2

 

33. Two proteins are similar in size but differ significantly in the number of acidic and basic amino acids. Which of the following techniques would be best suited to separating these two proteins?
  A) SDS-PAGE and gel-filtration chromatography
  B) isoelectric focusing and dialysis
  C) immunoprecipitation and affinity chromatography
  D) isoelectric focusing and ion-exchange chromatography
  E) None of the above.
  Ans:  D     Section:  5.2

 

34. Two proteins are similar in the number of acidic and basic amino acids but are different significantly in size. Which of the following techniques would be best suited to separating these two proteins?
  A) SDS-PAGE and gel-filtration chromatography
  B) isoelectric focusing and dialysis
  C) immunoprecipitation and affinity chromatography
  D) isoelectric focusing and ion-exchange chromatography
  E) None of the above.
  Ans:  A     Section:  5.2

 

35. Calmodulin is a calcium-binding protein expressed in eukaryotic cells. What two techniques would greatly reduce the number of steps to purify calmodulin?
  A) SDS-PAGE and gel-filtration chromatography
  B) isoelectric focusing and dialysis
  C) immunoprecipitation and affinity chromatography
  D) isoelectric focusing and ion-exchange chromatography
  E) None of the above.
  Ans:  C    Section:  5.2

 

36. You have isolated a protein, but by the time you have gotten it pure, you have only enough sample to do one type of analysis. Which of the following would you choose and why?
  A) MALDI-TOF mass spectrometry to determine as much sequence data as you can.
  B) ELIZA to identify any antigenic determinants.
  C) Amino Acid Composition Analysis because it can be done for the whole protein.
  D) 2D gel electrophoresis to determine charge and size data of the protein.
  E) Salting out to concentrate the protein for further study.
  Ans:  A    Section:  5.4

 

37. You are interested in studying a powerful enzyme that is expressed in low amounts. Which of the following would you choose to determine how much is found in the tissue of interest?
  A) MALDI-TOF mass spectrometry to determine as much sequence data as you can.
  B) ELIZA to identify any antigenic determinants.
  C) Amino Acid Composition Analysis because it can be done for the whole protein.
  D) 2D gel electrophoresis to determine charge and size data of the protein.
  E) Salting out to concentrate the protein for further study.
  Ans:  B    Section:  5.4

 

Short-Answer Questions

 

38. Why is an assay necessary for protein purification studies?
  Ans: An assay allows researchers to accurately measure the amount of the desired protein. This is important in determining if particular purification steps are effective in isolating the protein from the other cellular material.
  Section:  5.2

 

39. How is lactic acid dehydrogenase assayed?
  Ans: It is assayed by the increase in NADH present. NADH has a unique absorbance at 340 nm, and the reaction can be monitored by the increase in absorbance at this wavelength.
  Section:  5.2

 

40. How do gel-filtration and ion-exchange chromatography differ?
  Ans: Although both are used in purification, the properties of the column material determine how the separation is accomplished. Gel filtration is based on porous beads, and molecules are separated by size. In ion-exchange chromatography, the column material is charged with either positively or negatively charged molecules. Separation is based on the protein’s charge and affinity for the column media.
  Section:  5.2

 

41. How can a protein’s isoelectric point be used in protein purification?
  Ans: Isoelectric focusing is an electrophoretic technique in which a gradient charge is applied. Proteins migrate through the gradient field until they reach a point at which the pH is the same as the protein’s pI.
  Section:  5.2

 

42. What is the purpose of determining the specific activity, yield, and purification level of a protein purification protocol?
  Ans: The measurements allow one to determine if the individual steps were effective at selectively isolating the protein while maintaining its presence and activity. In order to successfully purify protein, both the yield and purification level must remain high.
  Section:  5.2

 

43. What type of information can be obtained from gradient centrifugation?
  Ans: This technique can be used to determine mass and density, and to investigate molecular shape and molecular interactions.
  Section:  5.3

 

44. Describe the Edman degradation method for protein-sequence analysis.
  Ans: A pure protein is reacted with phenylisothiocyanate, which binds to the free amino terminus. Under mildly acidic conditions, the derivatized amino acid is liberated, and can be identified by chromatography. The steps are repeated to identify the next amino acid exposed at the amino terminus.
  Section:  5.4

 

45. How can the amino acid sequences be used to design a DNA probe?
  Ans: Using the amino acid sequence, the genetic code and a process known as reverse genetics, a DNA sequence can be designed. (Codon degeneracy must be considered in the design.)
  Section:  5.4

 

46. Explain the process of immunoprecipitation.
  Ans: Antibodies to a specific protein are chemically fixed to an inert matrix. Protein mixtures containing the protein to be purified are incubated with the antibody/matrix such that only the protein to be purified binds. The unbound proteins are washed away leaving only the purified protein attached to the antibody.
  Section:  5.4

 

47.  Explain the trend of specific activity as a protein is purified.
  Ans:  As specific activity is expressed as units of enzyme per mg of protein, a crude sample with lots of protein will have a low specific activity.  A purified sample will have a much higher ratio of units of enzyme to total protein.  Thus, as a protein is purified the specific activity is increased
  Section:  5.2

 

48. List five possible steps in protein purification. Start with a technique used on a complex mixture of proteins such as a cell lysate through a series of steps to a pure protein.
  Ans:  homogenization, salting out, ion-exchange chromatography, gel filtration chromatography, affinity chromatography
  Section:  5.2

 

49.  Why is there a need for different digestion tools when fingerprinting a protein?
  Ans:  To generate overlapping peptides, short pieces of peptides are generated with one or two proteases and then further digested with other proteases.
  Section:  5.4

 

50.  A protein that on a SDS PAGE runs as a single 25,000 dalton band runs as a 75,000 dalton band on a native gel.  Why?
  Ans:  The protein in a SDS PAGE gel is denatured, while the native gel does not cause denaturation of the protein.  Thus, the protein before denaturing is a homotrimer of 75,000 daltons.
  Section:  5.2

 

 

 

Chapter 28        Fatty Acid Synthesis

 

 

Matching Questions

Use the following to answer questions 1–10:

 

Choose the correct answer from the list below. Not all of the answers will be used.

  1. a) malonyl CoA
  2. b) three
  3. c) four
  4. d) C16-acyl ACP
  5. e) cytosol
  6. f) glycolysis
  7. g) acetyl CoA
  8. h) b-hydroxybutyrate
  9. i) acetyl CoA carboylase
  10. j) AMP-activated protein kinase
  11. k) oxaloacetate
  12. l) malic
  13. m) citrate

 

1. Fatty acid synthesis takes place in ________________ stages.
  Ans: b
  Section: 28.1

 

2. Fatty acid synthesis primarily takes place in the cellular location ________________.
  Ans: e
  Section: 28.1

 

3. The reaction utilizing NADP+ and malate uses the ________________ enzyme.
  Ans: l
  Section: 28.1

 

4. ________________ is the product of the committed step in fatty acid synthesis.
  Ans: a
  Section: 28.1

 

5. The committed step in fatty acid synthesis is inactivated by the regulatory enzyme ________________.
  Ans: j
  Section: 28.2

 

6. Thioesterase determines the acyl-chain length by cleaving ________________.
  Ans: d
  Section: 28.1

 

7. The date rape drug GHB is an isomer of ________________.
  Ans: h
  Section: 28.1

 

8. The availability of the metabolite ________________ determines whether acetyl CoA, made from fatty acids, can enter the citric acid cycle.
  Ans: k
  Section: 28.1

 

9. ________________ is the key regulator of fatty acid metabolism.
  Ans: i
  Section: 28.3

 

10. The molecule ________________ is the form in which acetyl groups are carried across the mitochondrial membrane from the matrix to the cytoplasm.
  Ans: m
  Section: 28.1

 

 

Fill-in-the-Blank Questions

 

11. Activation of acetyl CoA results in the production of _____.
  Ans: malonyl CoA                                Section: 28.1

 

12. Citrate serves as a signal for a high-energy state as it stimulates _____ .
  Ans: acetyl CoA carboxylase                Section: 28.2

 

13. A biotin-deficient diet may lead to an increase of cytosolic _____.
  Ans: acetyl CoA                                  Section: 28.1

 

14. The major product of mammalian fatty acid synthesis is _____.
  Ans: a C16 fatty acid, palmitate                          Section: 28.2

 

15. The synthesis of fatty acids takes place in the _____of the cell.
  Ans: cytoplasm                                    Section: 28.1

 

16. The coenzyme required for fatty acid synthesis is _____.
  Ans: NADPH                                       Section: 28.1

 

17. The committed step of fatty acid synthesis is the formation of _____.
  Ans: malonyl CoA                                Section: 28.1

 

18. Acetyl CoA is transferred from the mitochondria to the cytoplasm in the form of _____.
  Ans: citrate                                           Section: 28.1

 

19. Double bonds are introduced into fatty acids in the _____compartment of the cell.
  Ans: endoplasmic reticulum                  Section: 28.2

 

20. Prostaglandins and thromboxanes are synthesized from _____, a 20-carbon fatty acid.
  Ans: arachidonate                                 Section: 28.2

 

 

Multiple-Choice Questions

 

21. Which of the following is an essential fatty acid?
  A) palmitate
  B) palmitoleate
  C) linoleate
  D) oleate
  E) All of the above.
  Ans: C              Section: 28.2

 

22. The reaction that catalyzes the addition of an activated two-carbon compound with an activated three-carbon compound is
  A) malonyl transacylase.
  B) b-ketoacyl synthase.
  C) b-ketoacyl ACP reductase.
  D) acetyl transacylase.
  E) enoyl ACP reductase.
  Ans: B              Section: 28.1

 

23. The carrier of an acyl chain through the synthetic protein complex is
  A) ACP.
  B) a serum albumin.
  C) acetyl coenzyme A.
  D) a biotin-activated complex.
  E) None of the above.
  Ans: A             Section: 28.1

 

24. Acetylation of serine on prostaglandin synthase leads to the reduction of which lipid mediator?
  A) prostacyclin
  B) thromboxane
  C) prostaglandins
  D) All of the above.
  E) None of the above.
  Ans: D             Section: 28.2

 

25. The function of the enzyme acyl CoA synthetase is
  A) lipolysis to release free glyceraldehyde.
  B) ATP-dependent reduction of acetyl-CoA prior to activation.
  C) ATP-dependent activation of fatty acids using CoA.
  D) All of the above.
  E) None of the above.
  Ans: C              Section: 28.2

 

26. Increasing the activity of adenylate kinase results in the activation of which enzyme?
  A) acetyl CoA carboxylase
  B) cAMP-dependent kinase
  C) PKC
  D) AMP-activated protein kinase
  E) citrate synthase
  Ans: D             Section: 28.3

 

27. Which compound inhibits the entry of fatty acyl CoA into the mitochondria as a function of the cell being in the high-energy state?
  A) malonyl CoA
  B) carnitine acyltransferase
  C) inhibition of acetyl CoA carboxylase
  D) All of the above.
  E) None of the above.
  Ans: A              Section: 28.3

 

28. Chronic ethanol ingestion alters carbohydrate metabolism and leads to a fatty liver due to an increase in which of the following?
  A) NADH
  B) NADPH
  C) ATP
  D) AMP
  E) None of the above.
  Ans: A             Section: 28.4

 

29. Insulin leads to
  A) an activation of fatty acid synthesis.
  B) an inhibition of fatty acid synthesis.
  C) a phosphorylation of proteins.
  D) a decrease of protein phosphatase hydrolysis of fatty acid synthesis enzymes.
  E) a decrease in pyruvate transport into mitochondria.
  Ans: A             Section: 28.4

 

30. What enzyme catalyzes the committed step in fatty acid synthesis?
  A) enoyl reductase
  B) acetyl CoA carboxylase
  C) transacylase  reductase
  D) 3-hydroxyacyl dehydratase
  E) None of the above.
  Ans: B              Section: 28.1

 

31. Enzymes from which of the following pathways are utilized for fatty acid synthesis?
  A) glycolysis
  B) the citric acid cycle
  C) the pentose phosphate pathway
  D) All of the above.
  E) None of the above.
  Ans: D              Section: 28.1

 

32. Acetyl carboxylaseis is regulated globally by
  A) allosteric inhibitors and activators.
  B) phosphorylation and  dephosphorylation.
  C) zymogen activation.
  D) the binding of cAMP.
  E) None of the above.
  Ans: B              Section: 28.3

 

33. How are fatty acids larger than the 16 carbons formed?
  A) by elongation reactions catalyzed by enzymes on the endoplasmic reticulum
  B) by 1-carbon additions at the mitochondrial membrane
  C) by elongation reactions catalyzed by enzymes in the peroxisomes
  D) All of the above.
  E) None of the above.
  Ans: A             Section: 28.2

 

34. Aspirin binds and blocks which of the following enzymes, thus explaining its multiple effects?
  A) phospholipase A2
  B) prostacyclin synthase
  C) diaceylglycerol lipase
  D) thromboxane synthase
  E) prostaglandin synthase
  Ans:  E     Section:  28.2

 

 

35. How are the consumption of eating corn oil and prostaglandin synthesis related?
  A) Prostaglandins are synthesized from membrane proteins originally derived from corn oil.
  B) ω-six fatty acids found in corn oil inhibit thromboxane synthase, shifting synthesis to prostaglandins.
  C) Corn oil contains linoleate, required for arachidonate synthesis.
  D) ω-three fatty acids found in corn oil inhibit thromboxane synthase, shifting synthesis to prostaglandins.
  E) Prostaglandidn synthesis and corn oil are not related.
  Ans:    C   Section:  28.2

 

36. How does the cell ensure that fats are not synthesized when the energy charge of the cell is low?
  A) Acetyl CoA carboxylase 1 is switched off by phosphorylation.
  B) AMP-activated protein kinase is activated by AMP.
  C) Acetyl CoA carboxylase 1 exists as inactive dimers unless citrate and ATP levels are high.
  D) Polymerization of active acetyl CoA carboxylase I is facilitated by the protein MIG12.
  E) All of the above.
  Ans:    E   Section:  28.3

 

37. Fatty acid synthesis is regulated by hormone depending on feeding vs. fasting and recent exercise vs. no recent exercise. Which hormones are active and what is their mechanism of action of the(se) hormone(s) after exercise and a meal?
  A) Insulin stimulates fatty acid synthesis by activating acetyl CoA carboxylase 1.
  B) Insulin stimulates the mobilization of fatty acids for β oxidation.
  C) Epinephrine stimulates the mobilization of fatty acids and stimulates their accumulation as triacylglycerols.
  D) Glucagon activates the carboxylase by enhancing the phosphorylation of AMPK.
  E) Epinephrine stimulates AMPK, preventing the phosphorylation of acetyl CoA carboxylase 1.
  Ans:   A    Section:  28.4

 

38. What are the conditions that lead to a “beer gut” due to the excess consumption of alcohol?
  A) NADH produced from the metabolism of ethanol stimulates the citric acid cycle for glucose-derived acetyl CoA.
  B) Excess ethanol metabolism leads to an accumulation of NADH that inhibits fatty acid metabolism.
  C) NADH stimulates citric acid cycle enzymes that stimulates glucose-derived acetyl CoA metabolism.
  D) NADH inhibits ketone body formation, stimulating glucose rather than fatty acid metabolism.
  E) The processing of acetate in the liver becomes inefficient leading to a pH imbalance in liver cells, reducing enzyme efficiency in general.
  Ans: B      Section:  28.4

 

 

Short-Answer Questions

 

39. What are the four physiological roles for fatty acids?
  Ans: Fatty acids are important (1) as building blocks of phospholipids and glycolipids, (2) for modification of proteins via covalent lipid attachment, (3) as fuel molecules, and (4) as precursors of hormones and messengers.
  Section: Introduction

 

40. What are the similarities between fatty acid synthesis and degradation?
  Ans: The processes are very similar, only in reverse directions. The intermediates are structurally similar and the steps are in similar order.
  Section: 28.1.

 

41. Describe the chemistry for fatty acid synthesis at the stage when a two-carbon molecule reacts with a three-carbon molecule to give a four-carbon molecule and a 1-carbon molecule.
  Ans: This is the activation and condensation of malonyl CoA and acetyl CoA. The loss of a CO2 group in the condensation results in a new four carbon acyl chain, acetoacetyl CoA.
  Section: 28.1

 

42. What is citrate’s role in fatty acid synthesis?
  Ans: Citrate is synthesized in the mitochondria by the condensation of acetyl CoA and oxaloacetate. The citrate is transported into the cytoplasm, where it undergoes the reverse reaction, making acetyl CoA available for fatty acid synthesis. Thus, citrate is the acetyl group carrier from the mitochondria to the cytoplasm.
  Section: 28.1

 

43. NADPH-reducing equivalents important for the biosynthesis of fatty acids come from several sources. Explain.
  Ans: One NADPH molecule is produce by the fatty acid synthetic pathway as it is transferred into the cytosol. The additional reducing equivalents come from the pentose phosphate pathway, one of the main products of the pathway.
  Section: 28.1

 

44. How is the structure of fatty acid degradation enzymes different from that of synthesis enzymes?
  Ans: Fatty acid synthesis differs from degradation by being organized into a multifunctional enzyme complex. This makes the process more efficient.
  Section: 28.1

 

45. Describe the regulation of fatty acid synthesis by AMP and citrate.
  Ans: AMP is a low-energy molecule that is produced by the actions of adenylate kinase. AMP activates a separate protein kinase, which phosphorylates and inhibits carboxylase. Citrate, a product of acetyl CoA transport into the cytoplasm, can override this inhibition by allosteric mechanism.
  Section: 28.2

 

46. Where are the enzymes for fatty acid elongation and desaturation in eukaryotes?
  Ans: In eukaryotes, the enzymes that catalyze elongation and desaturation reactions are located on the cytoplasmic surface of the endoplasmic reticulum.
  Section: 28.2

 

47. Why are linoleate (18:2) and linolenate (18:3) considered essential fatty acids in mammals?
  Ans: Mammals lack the enzymes to introduce double bonds at carbon atoms beyond C9; therefore, mammals cannot synthesize linoleate (18:2), which has a double bond at C12 and linolenate (18:3), which has double bonds at C12 and C15. These two fatty acids must be consumed in the diet.
  Section: 28.2

 

48. Describe the allosteric stimulatory effect of citrate on acetyl CoA carboxylase.
  Ans: The inactive form of acetyl CoA carboxylase is a dimer. Citrate stimulates the polymerization of these dimers into the active filamentous form.
  Section: 28.3

 

49. In fatty acid synthesis, what is the compound X in the following metabolic conversion?

 

  Ans:
  Section: 28.1

 

50. Explain this statement: “Fats burn in the flame of carbohydrates.”
  Ans: This means that the acetyl CoA formed from fatty acids cannot enter the citric acid cycle unless fat and carbohydrate consumption are balanced. Insufficient carbohydrate intake lowers the availability of oxaloacetate, which is made from pyruvate via pyruvate carboxylase. The acetyl CoA cannot react with oxaloacetate, and thus cannot enter the cycle. It is diverted to a different pathway.
  Section: 28.1

 

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