BIOCHEMISTRY - L. Stryer - 1984

VOLUME 2

PART II GENERATION AND STORAGE OF METABOLIC ENERGY

CHAPTER 12. GLYCOLYSIS

QUESTIONS AND PROBLEMS

1. CARBOHYDRATES that differ in configuration only at their anomeric carbons are anomers. Epimers differ in configuration at specific carbon atoms other than the anomeric carbon. Indicate whether each of the following pairs of sugars consists of anomers, epimers, or an aldose-ketose pair.

a) D-glyceraldehyde and dihydroxyacetone.

b) D-glucose and D-mannose.

c) D-glucose and D-fructose.

d) α-D-glucose and β-D-glucose.

e) D-ribose and D-ribulose.

f) D-galactose and D-glucose.

2. Glucose labeled with ¹⁴C at C-1 is incubated with glycolytic Enzymes and the necessary Cofactors. What is the distribution of ¹⁴C in the resulting Pyruvate? (Assume that the interconversion of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate is very rapid compared with the subsequent step.)

3. Write the net equation for The conversion of glucose into lactate.

a) Calculate the standard free-energy change for this reaction, using the data in Table 12.2 (Section 12.8) and given that ∆G⁰' for the reaction Pyruvate + NADH + H⁺ ⇄ Lactate + NAD⁺ is -6 kcal.

b) What is the free-energy change (∆G', not ∆G⁰') of this reaction at the following concentrations of reactants: glucose - 5 mM; lactate - 0.05 mM; ATP - 2 mM; ADP - 0.2 mM; Pi - 1 mM?

4. What is the equilibrium ratio of phosphoenolpyruvate to pyruvate under standard conditions when [ATP]/[ADP] = 10?

5. What are the equilibrium concentrations of fructose 1,6-bisphosphate, dihydroxyacetone phosphate, and glyceraldehyde 3-phosphate when fructose 1,6-bisphosphate (1 mM) is incubated with aldolase under standard conditions?

6. 3-Phosphoglycerate, uniformly labeled with ¹⁴C, is incubated with 1,3-BPG labeled with ³²P at C-1. What is the distribution of the radioactive isotope in the 2,3-BPG formed upon addition of bisphosphoglycerate mutase?

7. Xylose has the same Structure as glucose except that it has a hydrogen atom at C-5 instead of a hydroxymethyl group. The rate of ATP Hydrolysis by hexokinase is markedly increased by The addition of xylose. Why?

8. The Active Site of phosphoglycerate mutase contains two Histidine residues parallel to each other and separated by 4 Å. Propose a likely catalytic mechanism.