MBioS 303 Recitation

Introductory Biochemistry, Summer 2008

Practice Problem Set #7: General Metabolism Concepts, Glycolysis and the TCA Cycle

(1) Glucose 1-pohsphate is converted to fructose 6-phosphate in two successive reactions:

Glucose-1-P � glucose-6-P ΔG⁰’ = -1.7 kcal/mol

Glucose-6-P �fructose-6-P ΔG⁰’ = -0.4 kcal/mol

What is the ΔG⁰’ for the overall reaction?

a. -2.1 kcal/mol

b. -1.7 kcal/mol

c. -1.3 kcal/mol

d. 1.3 kcal/mol

e. 2.1 kcal/mol

(2) Which of the following are ways by which two reactions can be coupled energetically to each

other?

a. As common intracellular components of a compartment, two reactions become

automatically coupled.

b. An ionic gradient across a membrane that is formed by one reaction can drive

another reaction that uses the gradient to render it exergonic.

c. A shared, common intermediate can couple two reactions.

d. A protein that is activated by binding another molecule or by being covalently

modified can provide energy to drive another reaction.

(3) Which of the following are high-energy compounds?

a. Glucose-6-phosphate

b. Adenosine diphosphate

c. Fructose-6-phosphate

d. 1,3-bisphosphoglycerate

e. Dihydroxyacetone phosphate

(4) Which of the following answers complete the sentence correctly? NAD+

a. is a flavin nucleotide.

b. is the major electron acceptor used in fuel metabolism.

c. contains a nicotinamide ring that accepts a hydride ion during reduction.

d. loses a plus charge upon reduction.

e. contains ATP as a part of its structure.

(5) Match the four cofactors in the left column with the appropriate structural features and

properties from the right column.

a. ATP (1) nicotinamide ring (5) ribose group

b. FAD (2) adenine group (6) electron transfer

c. NAD+ (3) phosphoanhydride bond (7) phosphate transfer

(4) isoalloxazine ring

(6) ATP and NADH release large amounts of free energy upon the transfer of the phosphate group

to H2O and electrons to O2, respectively. However, both molecules are relatively stable in the

presence of H2O or O2. Explain why.

(7) What are the three primary fates of pyruvate?

(8) For each of the following types of chemical reactions, give at least one example of a glycolytic

enzyme that carries out such a reaction.

a. Aldol cleavage

b. Dehydration

c. Phosphoryl transfer

d. Phosphoryl shift

e. Isomerization

f. Phosphorylation coupled to oxidation

(9) The steps of glycolysis between glyceraldehydes 3-phosphate and 3-phosphyglycerate involve all

of the following except:

a. ATP synthesis.

b. Utilization of Pi.

c. Oxidation of NADH to NAD+.

d. Formation of 1,3-bisphosphyglycerate.

e. Catalysis by phosphoglycerate kinase.

(10) Which of the following answers complete the sentence correctly? The phosphofructokinase

and the pyruvate kinase reactions are similar in that

a. Both generate ATP.

b. Both involve a “high-energy” sugar derivative.

c. Both involve three-carbon compounds.

d. Both are essentially reversible.

e. Both enzymes undergo induced-fit rearrangements after binding of the substrate.

(11) If the C-1 carbon of glucose were labeled with 14C, which of the carbon atoms in pyruvate

would be labeled after glycolysis?

a. The carboxylate carbon c. The methyl carbon

b. The carbonyl carbon

(12) Starting with fructose 6-phosphate and proceeding to pyruvate, what is the net yield of ATP

molecules?

a. 1

b. 2

c. 3

d. 4

e. 5

(13) Since lactate is a “dead-end” product of metabolism in the sense that its sole fate is to be

reconverted into pyruvate, what is the purpose of its formation?

(14) The essentially irreversible reactions that control the rate of glycolysis are catalyzed by which

of the following enzymes?

a. Pyruvate kinase

b. Aldolase

c. Glyceraldehyde 3-phoosphate dehydrogenase

d. Phosphofructokinase

e. Hexokinase

f. Phosphyglycerate kinase

(15) What are the potential advantages of a multienzyme complex with respect to the isolated

enzyme components?

(16) Examine Figure 1 (near the bottom). Without using your notes or textbook, can

you go through the figure and label the metabolic intermediates (labeled A through J) and the

enzymes (labeled 1 through 10)? Also be sure to label where ADP and ATP are used and

formed, and where NAD+ and NADH are oxidized or reduced (indicated by red boxes).

(17) Examine Figure 2 (near the bottom). Without using your notes or textbook, can

you go through the figure and label the metabolic intermediates (labeled A through K) and the

enzymes (labeled 1 through 8)? Also be sure to label where energy (in the form of ATP or GTP)

and electron carriers (in the form of NAD+/NADH or FAD/FADH2) are oxidized and reduced

(indicated by red boxes). You do need to know which specific “energy molecule” or electron

carrier is used at each step!

FIGURE 1

FIGURE 2