Chapter 31 Amino 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.
a) atmospheric nitrogen (N2)
b) 3-phosphoglycerate
c) cumulative
d) nitrogen fixation
e) B12
f) histidine
g) tetrahydrofolate
h) committed
i) pyridoxal phosphate
j) enzyme multiplicity
k) MoFe cofactor
l) ammonia (NH3)
1.
_______________ is the original nitrogen source for the nitrogen found in amino acids.
2.
The process of converting N2 to NH3 is called _______________.
Ans:
d
Section: Introduction
3.
_______________ is the site of nitrogen fixation by nitrogenase enzymes.
Ans:
k
Section: 31.1
4.
The precursor for serine, cysteine, and glycine amino acid biosynthesis is _______________.
Ans:
b
Section: 31.2
5.
A versatile carrier of one-carbon units is _______________.
Ans:
g
Section: 31.2
6.
Methylcobalamine is derived from vitamin _______________.
Ans:
Section: 31.2
7.
_______________ is a cofactor for transamination reactions.
Ans:
i
Section: 31.2
Ans:
Section: Introduction
Chapter 31 Amino Acids Synthesis
2
8.
The final product pathway that inhibits an enzyme that catalyzes its production typically takes
place at the _______________ step.
9.
Glutamine synthesis is inhibited by _______________ feedback inhibition.
Ans:
Section: 31.3
10.
Isozymes, or multiple enzymes with the same identical catalytic properties but with different
regulation, are an example of _______________.
Ans:
Section: 31.3
Fill–in-the-Blank Questions
11.
Only a few prokaryotes, such as _____, are able convert N2 to ammonia.
Ans: nitrogen-fixing bacteria Section: Introduction
12.
_____ ATP molecules are hydrolyzed for each N2 reduced.
Ans: At least 16 Section: 31.1
13.
The α-amino group found in most amino acids comes from _____ through a transamination
reaction.
Ans: glutamate Section: 31.1
14.
Glutamine synthase adds NH3 to _____ to make glutamine.
Ans: glutamate Section: 31.1
15.
Glutamate is the precursor for the amino acids glutamine, proline, and _____.
Ans: arginine Section: 31.2
16.
Methyl, methylene, and _____ units can be carried by tetrahydrofolate.
Ans: formyl Section: 31.2
17.
Homocysteine is an intermediate in the synthesis of cysteine and _____.
Ans: methionine Section: 31.2
18.
The enzyme _____ is regulated by cumulative feedback inhibition.
Ans: glutamine synthase Section: 31.3
19.
The binding of serine to 3-phosphoglycerate dehydrogenase induces a _____ in Vmax.
Ans: reduction Section: 31.3
20.
Metabolic pathways that have alternate products are often regulated by _____ and _____.
Ans: feedback inhibition; activation Section: 31.3
Ans:
h
Section: 31.3
Chapter 31 Amino Acids Synthesis
3
Multiple-Choice Questions
21.
Amino acid synthesis is generally regulated by
A)
turnover.
B)
diet.
C)
feedback and allosteric enzyme regulation.
D)
A and B.
E)
A, B, and C.
22.
Organisms capable of carrying out reduction of atmospheric nitrogen include
A)
some bacteria and archaea.
B)
higher eukaryotic organisms, such as mammals.
C)
all plants.
D)
All of the above.
E)
None of the above.
Ans: A Section: 31.1
23.
The electrons for the reduction of molecular nitrogen are donated by
A)
proteins.
B)
NADPH.
C)
ferredoxin.
D)
None of the above.
E)
All of the above.
Ans: C Section: 31.1
24.
The carbon skeletons for amino acids are intermediates found in
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: 31.2
25.
Essential amino acids differ from nonessential amino acids in that
A)
nonessential amino acids are synthesized in simple reactions compared to many for most
essential amino acids.
B)
essential amino acids are generally synthesized directly from citric acid cycle
intermediates, but nonessential amino acids are not.
C)
microorganisms and animals cannot synthesize essential amino acids but plants can.
D)
animals cannot synthesize essential amino acids because they have lost the ability to carry
out transamination reactions.
E)
None of the above.
Ans: A Section: 31.2.
Ans: C Section: 31.3
Chapter 31 Amino Acids Synthesis
4
26.
S-adenosylmethionine carries which groups?
A)
methyl
B)
CO2
C)
ammonia
D)
None of the above.
E)
All of the above.
27.
This amino acid, in high levels, is correlated with the damage of cells lining the blood vessels.
A)
serine
B)
cysteine
C)
S-adenosylmethionine
D)
citrulline
E)
homocysteine
Ans: E Section: 31.2
28.
Essential amino acids are synthesized by:
A)
microorganisms.
B)
humans.
C)
plants.
D)
A and B.
E)
A and C.
Ans: E Section: 31.2
29.
Which amino acid is added to indole to form tryptophan?
A)
glutamine
B)
serine
C)
tyrosine
D)
All of the above.
E)
None of the above.
Ans: B Section: 31.2
30.
Erythrose 4-phosphate is a precursor to the amino acids
A)
tryptophan, tyrosine, and phenylalanine.
B)
tryptophan and phenylalanine.
C)
tyrosine and phenylalanine.
D)
tryptophan, tyrosine, phenylalanine, and serine.
E)
None of the above.
Ans: A Section: 31.2
31.
Through what process might feedback inhibition processes have evolved?
A)
duplication of genes encoding catalytic domains
B)
evolution of homologous subunits in the enzyme catalyzing the committed step
C)
linking specific regulator domains to catalytic domains
D)
linking of multiple regulatory domains
E)
All of the above.
Ans: C Section: 31.3
Ans: A Section: 31.2
Chapter 31 Amino Acids Synthesis
5
32.
An example of a reaction controlled by enzyme multiplicity is
A)
phosphorylation of asparagine by aspartokinases.
B)
phosphorylation of aspartate by aspartokinases.
C)
phosphorylation of glutamine by glutamine synthetase.
D)
All of the above.
E)
None of the above.
33.
Which gaseous plant hormone is involved in triggering ripening?
A)
melanin
B)
epinephrine
C)
ethylene
D)
A and B.
E)
A and C.
Ans: C Section: 31.2
34.
The activated methyl cycle involves the production and use of
A)
glutamine.
B)
glycine.
C)
heterocysteine.
D)
homocysteine.
E)
methanol.
Ans: D Section: 31.2
35.
The rates of synthesis of amino acid metabolic pathways often depends on the
A)
committed step.
B)
allosteric regulation.
C)
feedback inhibition.
D)
All of the above.
E)
None of the above.
Ans: D Section: 31.3
36.
The making of carbon-carbon bonds requires energy. How does the activated methyl cycle
provide energy for methyl group transfer to a wide variety of acceptors?
A)
The side-chain methylene group of serine is transferred to tetrahydrofolate, a carrier of
one-carbon units.
B)
The fully oxidized one-carbon unit, CO2, is carried by biotin.
C)
The most reduced form of one-carbon groups carried by tetrahydrofolate is the methyl
group.
D)
Transmethylation reactions are carried out by pyricoxal phosphate-dependent
methyltransferases.
E)
The methyl group of methionine is activated by the transfer of an adenosyl group to the
sulfur atom of methionine.
Ans: E Section: 31.2
Ans: B Section: 31.3
Chapter 31 Amino Acids Synthesis
6
37.
Increased synthesis of which of the following amino acids might affect DNA production?
A)
histidine and tryptophan
B)
aspartate and glutamate
C)
threonine and methionine
D)
cysteine and glycine
E)
valine and leucine
38.
Insufficient amounts of this amino acid would not only inhibit protein synthesis, but also
phostidylcholine and phostidylethanolamine.
A)
glutamine
B)
histidine
C)
phenylalanine
D)
methionine
E)
alanine
Ans: D Section: 31.2
39.
In Chapter 22, we learned that ferredoxin is a strong reductant in the ferredoxin-NADP+
reductase. Where else is ferredoxin’s reducing power required?
A)
glutamine synthetase
B)
reductase (Fe protein)
C)
nitrogenase (MoFe protein)
D)
glutamate dehydrogenase
E)
aspartate transaminase
Ans: B Section: 31.1
40.
Enzymes that catalyze the same reaction but are regulated differently is a strategy known as
A)
sequential feedback inhibition.
B)
end-product inhibition.
C)
substrate-limited inhibition.
D)
enzyme multiplicity.
E)
cumulative feedback inhibition.
Ans: D Section: 31.3
Short-Answer Questions
41.
What is significant about many of the intermediates in amino acid biosynthesis?
and thus are critical to anabolic and catabolic paths. In this way, intermediates can play a
dual role, depending on the energy status of the organism.
Section: 31.2
Ans: A Section: 31.2
Chapter 31 Amino Acids Synthesis
7
42.
What determines the range of one-carbon units carried by tetrahydrofolate?
43.
Describe the process and proteins involved in nitrogen fixation.
nitrogenase. In this process, electrons are provided by the reductase to the nitrogenase to
use. The reaction is driven by the hydrolysis of ATP. See Figure 31.1 for further details.
Section: 31.1
44.
What is the MoFeco factor?
nitrogenase heterotetramer binds two cofactors via amino acid links.
Section: 31.1
45.
What is a major difference between the amino acid biosynthetic capacity of prokaryotic
organisms and humans?
own needs and must have it supplied in their diet.
Section: 31.2
46.
What do S-adenosylmethionine and fruit ripening have in common?
ripening, and often premature spoiling, of fruits.
Section: 31.2
47.
Draw homocysteine.
COO–
Section: 31.2
48.
Describe the regulation of the enzyme threonine deaminase.
acids made and helps balance the relative amounts.
Section: 31.3
formimino, or methenyl groups.
Section: 31.2
Chapter 31 Amino Acids Synthesis
8
49.
What is enzyme multiplicity?
50.
What is the advantage of the cumulative enzymatic regulation of glutamine synthetase activity?
flow of nitrogen. Allosteric control is increased and each activator or inhibitor can
specifically contribute to regulation.
Section: 31.3
51.
What would be the result of a pathway such as that shown in Figure 31.12 if only one enzyme
catalyzed the first reaction? What if there was inhibition only by X and not by Y?
other enzyme rates, not limited to the cellular needs of each product. The primary product
of inhibition only by X would be Y and not X.
Section: 31.3
52.
Describe the effect of cumulative inhibition.
effect, even in the presence of the other inhibitors.
Section: 31.3
but differ somewhat in structure and sequence, are regulated by different molecules. In
this way, various biomolecules can influence the overall amount of a product made.
Section: 31.3