Biochem Exam 3

Biochem Exam 3 QUESTIONS and
WELL-VERIFIED ANSWERS

Which of the following pathways use intermediates of the citric acid cycle?

I. glucogenesis
II. amino acid biosynthesis
III. fatty acid oxidation
IV. glycolysis

A. I, II
B. I, III
C. II, IV
D. III, IV
E. I, IV - ANSWER: A. I, II

Which of the monosaccharides seen below are L sugars?

A) C and D
B) A and C
C) A and B
D) A, B, and C
E) B and C - ANSWER: A) C and D

At equilibrium in solution, D- Glucose consists of a mixture of its anomers. Which
statement most accurately describes the solution?

A) Consists of approximately equal amounts of the a-and B-anomers

B) the a-anomer is more stable and is slightly preferred over the B-anomer

C) the B-anomer predominates over the a-anomer by a ratio of approximately 2:1

D) Straight chain form is present in high concentration

E) None of the above - ANSWER: C) the B-anomer predominates over the a-anomer by
a ratio of approximately 2:1

The structure below shows a Fischer projection of D-idose. Which of the structures
below represents B-D-idopyranose?

,A) A
B) B
C) C
D) D
E) E - ANSWER: E) E

In the following structure, which carbon is the anomeric carbon?

A) A
B) B
C) C
D) D
E) E - ANSWER: E

The configuration around which carbon atom shown in the figure determines whether
this is a D or an L sugar?

A) A
B) B
C) C
D) D
E) E - ANSWER: A) A

Which structures shown in the picture below represent reducing sugars?

A) A
B) D
C) C and D
D) A, B, C, and D
E) A, B, and C - ANSWER: E) A, B, and C

To be a reducing sugar, you need a free aldehyde or ketone group (aka last in the
chain), A, B, and C have free ketones on the top part of their chain. *(Remember this
note for the exam there's question asking which is not a reducing sugar)*

Amylopectin contains primarily ___ glycosidic bonds with ____ glycosidic bonds as
branch points

A) B (1->4); a (1->6)

B) a (1->4); B (1->6)

C) B (1->4); a (1->4)

D) a (1->4); a (1->2)

, E) a (1->4); a (1->6) - ANSWER: E) a (1->4); a (1->6)

In which of the following metabolic conversions is ATP required during glycolysis?
I. fructose-6-phosphate -> fructose-1,6-bisphosphate
II. glucose -> glucose-6-phosphate
III. fructose-1,6-bisphosphate -> dihydroxyacetone phosphate + glyceraldehyde-3-
phosphate
IV. glucose-6-phosphate -> fructose-6-phosphate

A) I only
B) II only
C) I, II
D) I, III
E) I, IV - ANSWER: C) I, II

- catalyzed by phosphofructokinase in (i), catalyzed by hexokinase in (II), both need
ATP (memorize these they might be individually on the exam)

Which of the following is a potent activator of phosphofructokinase in mammals?

A) fructose-1,6-bisphosphate
B) fructose-6-phosphate
C) glucose-6-phosphate
D) glyceraldehyde-3-phosphate
E) fructose-2,6-bisphosphate - ANSWER: E) fructose-2,6-bisphosphate

The enzyme ___ forms a schiff base upon formation of the enzyme-substrate complex
allowing aspartate-mediated cleavage of the substrate
A) Aldolase
B) phosphoglucose isomerase
C) phosphoglucose mutase
D) glucose-6-phosphatase
E) hexokinase - ANSWER: A) Aldolase

The active site of aldolase contains a Lys residue that forms a(n) ____ and a(n) Asp
residue that participates in ___ reactions
A) Schiff base; acid-base
B) amide; isomerization
C) secondary amine; acid-base
D) amide; acid-base
E) Schiff base; isomerization - ANSWER: A) Schiff base; acid-base

In the reaction catalyzed by aldolase, the bond broken is between C-3 and C-4 of the
substrate. Which functional groups are present on these two carbons (C-3 and C-4) in
the products?