Question 1

Which statement is NOT true of the reaction catalyzed by ribonucleotide reductase?

Accepted Answer

A)   Glutathione is part of the path of electron transfer.
B)   It acts on nucleoside diphosphates.
C)   Its mechanism involves formation of a free radical.
D)   There is a separate enzyme for each nucleotide (ADP, CDP, GDP, UDP) .
E)   Thioredoxin acts as an essential electron carrier. D

Question 2

In the synthesis of serine from 3-phosphoglycerate, which answer lists the CORRECT order and type of reactions?

Accepted Answer

A)   reduction, hydrolysis, transamination
B)   oxidation, transamination, hydrolysis
C)   reduction, transamination, hydrolysis
D)   oxidation, hydrolysis, transamination
E)   hydrolysis, transamination, reduction B

Question 3

Nonessential amino acids:

Accepted Answer

A)   are amino acids other than those required for protein synthesis.
B)   are not utilized in mammalian proteins.
C)   are synthesized by plants and bacteria, but not by humans.
D)   can be synthesized in humans as well as in bacteria.
E)   may be substituted with other amino acids in proteins. D

Question 4

Why is it necessary to have protein in our (human) diets?

Accepted Answer

The answer of Why is it necessary to have protein...

Question 5

Which statement is FALSE regarding the proposed mechanism for glutamine amidotransferases?

Accepted Answer

A)   Part of the mechanism includes the formation of a thioester to a cysteine.
B)   A hydrolysis reaction releases glutamine from the active site.
C)   Ammonia is released from one substrate before reacting with the second substrate.
D)   Phosphorylation is often used to activate the substrate accepting the amino group.
E)   Two portions of the enzymes are connected by an "ammonia channel."

Question 6

De novo purine biosynthesis is distinguished from de novo pyrimidine biosynthesis by:

Accepted Answer

A)   condensation of the completed purine ring with ribose phosphate
B)   incorporation of CO2.
C)   inhibition by azaserine (a glutamine analog) .
D)   participation of aspartate.
E)   participation of PRPP (phosphoribosyl pyrophosphate) .

Question 7

Which statement is NOT true about glutamine amidotransferases?

Accepted Answer

A)   These enzymes proceed via a covalent intermediate.
B)   Ammonia is released into a channel.
C)   Glutamate is a product of the reaction.
D)   ATP is needed to activate the glutamine.
E)   A Cys at the active site is critical for the activity of these enzymes.

Question 8

Describe and contrast, with diagrams, concerted (cumulative) feedback regulation and sequential feedback inhibition.

Accepted Answer

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Question 9

Azaserine is a structural analog of glutamine. It is a competitive inhibitor of many enzymes that use glutamine as substrates. Name) three biosynthetic products whose synthesis you would expect to be inhibited by azaserine. Do you think that eating azaserine would be immediately fatal? Why or why not?

Accepted Answer

The answer of Azaserine is a structural analog of glutamine....

Question 10

Which process below is NOT required in the conversion of dCTP into dTTP?

Accepted Answer

A)   deamination
B)   methylation
C)   phosphate hydrolysis
D)   phosphate addition
E)   reduction

Question 11

Give the name and structure of the glycolytic or citric acid cycle intermediate that has the same carbon skeleton as (a) alanine, (b) glutamate, (c) aspartate.

Accepted Answer

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Question 12

What is the role of leghemoglobin in root nodules of legumes with respect to nitrogen fixation?

Accepted Answer

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Question 13

In bacteria, the amino acids listed below can be derived directly or indirectly from serine, alanine, aspartate, glutamate, or chorismate. Indicate below which of these "parent" compounds provides the carbon skeleton for each amino acid:
Parent compound
Asparagine
__________________
Tryptophan
__________________
Glycine
__________________
Methionine
__________________
Threonine
__________________
Cysteine
__________________
Proline
__________________
Isoleucine
__________________
Phenylalanine
__________________

Accepted Answer

The answer of In bacteria, the amino acids listed below...

Question 14

Match the signaling molecule with its amino acid precursor (a given precursor may be used more than once or not at all):

Accepted Answer

The answer of Match the signaling molecule with its amino...

Question 15

Which statement is NOT a similarity in the synthesis of isoleucine, valine, and leucine?

Accepted Answer

A)   Pyruvate is the starting compound for synthesis of all these amino acids.
B)   Pyridoxal phosphate is a required cofactor in the synthesis of all these amino acids.
C)   These are all essential amino acids in humans.
D)   An  α\alphaα -keto acid is the immediate precursor for all three synthetic pathways.
E)   Acetyl-CoA is required as a substrate in all three synthetic pathways.

Question 16

Which enzyme is NOT involved in the assimilation of inorganic nitrogen into an organic molecule?

Accepted Answer

A)   arginase
B)   glutamate dehydrogenase
C)   glutamate synthase
D)   glutamine synthetase
E)   dinitrogenase

Question 17

Which reaction step in the synthesis of proline is nonenzymatic?

Accepted Answer

A)   the phosphorylation of the side chain
B)   the reaction that generates an aldehyde product
C)   the cyclization step
D)   the reaction that releases inorganic phosphate as a product
E)   the reaction that converts a double bond to a single bond

Question 18

Draw the structure of 5'-GMP. Indicate with an arrow the atom(s) derived from glutamine's amide group(s).

Accepted Answer

The answer of Draw the structure of 5'-GMP. Indicate with...

Question 19

The bacteria A. vinelandii uncouples oxidative phosphorylation during nitrogen fixation for what reason?

Accepted Answer

A)   It increases the temperature so that the enzymes will function at maximum efficiency.
B)   It ensures that the citric acid cycle is fully active and providing substrates for nitrogen fixation.
C)   It ensures that ATP is not present to inhibit nitrogen fixation.
D)   It maintains a low level of reduced cofactors.
E)   It ensures that oxygen concentrations are kept low to prevent interference with enzymes.

Question 20

CMP, UMP, and TMP all have _____ as a common precursor.

Accepted Answer

A)   adenosine
B)   aspartate
C)   glutamine
D)   inosine
E)   S-adenosyl methionine

Exam 22: Biosynthesis of Amino Acids, Nucleotides, and Related Molecules