Chapter 28 Fatty 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) malonyl CoA
b) three
c) four
d) C16-acyl ACP
e) cytosol
f) glycolysis
g) acetyl CoA
h) -hydroxybutyrate
i) acetyl CoA carboylase
j) AMP-activated protein kinase
k) oxaloacetate
l) malic
m) citrate
1.
Fatty acid synthesis takes place in ________________ stages.
2.
Fatty acid synthesis primarily takes place in the cellular location ________________.
Ans: e
3.
The reaction utilizing NADP+ and malate uses the ________________ enzyme.
Ans: l
Section: 28.1
4.
________________ is the product of the committed step in fatty acid synthesis.
Ans: a
Section: 28.1
5.
The committed step in fatty acid synthesis is inactivated by the regulatory enzyme
________________.
Ans: j
Section: 28.2
6.
Thioesterase determines the acyl-chain length by cleaving ________________.
Ans: d
Section: 28.1
7.
The date rape drug GHB is an isomer of ________________.
Section: 28.1
Ans: b
Chapter 28 Fatty Acid Synthesis
2
8.
The availability of the metabolite ________________ determines whether acetyl CoA, made
from fatty acids, can enter the citric acid cycle.
9.
________________ is the key regulator of fatty acid metabolism.
Ans: i
Section: 28.3
10.
The molecule ________________ is the form in which acetyl groups are carried across the
mitochondrial membrane from the matrix to the cytoplasm.
Ans: m
Section: 28.1
Fill–in-the-Blank Questions
11.
Activation of acetyl CoA results in the production of _____.
Ans: malonyl CoA Section: 28.1
12.
Citrate serves as a signal for a high-energy state as it stimulates _____ .
Ans: acetyl CoA carboxylase Section: 28.2
13.
A biotin-deficient diet may lead to an increase of cytosolic _____.
Ans: acetyl CoA Section: 28.1
14.
The major product of mammalian fatty acid synthesis is _____.
Ans: a C16 fatty acid, palmitate Section: 28.2
15.
The synthesis of fatty acids takes place in the _____of the cell.
Ans: cytoplasm Section: 28.1
16.
The coenzyme required for fatty acid synthesis is _____.
Ans: NADPH Section: 28.1
17.
The committed step of fatty acid synthesis is the formation of _____.
Ans: malonyl CoA Section: 28.1
18.
Acetyl CoA is transferred from the mitochondria to the cytoplasm in the form of _____.
Ans: citrate Section: 28.1
19.
Double bonds are introduced into fatty acids in the _____compartment of the cell.
Ans: endoplasmic reticulum Section: 28.2
20.
Prostaglandins and thromboxanes are synthesized from _____, a 20-carbon fatty acid.
Ans: arachidonate Section: 28.2
Multiple-Choice Questions
Ans: k
Section: 28.1
Chapter 28 Fatty Acid Synthesis
3
21.
Which of the following is an essential fatty acid?
A)
palmitate
B)
palmitoleate
C)
linoleate
D)
oleate
E)
All of the above.
22.
The reaction that catalyzes the addition of an activated two-carbon compound with an activated
three-carbon compound is
A)
malonyl transacylase.
B)
-ketoacyl synthase.
C)
-ketoacyl ACP reductase.
D)
acetyl transacylase.
E)
enoyl ACP reductase.
Ans: B Section: 28.1
23.
The carrier of an acyl chain through the synthetic protein complex is
A)
ACP.
B)
a serum albumin.
C)
acetyl coenzyme A.
D)
a biotin-activated complex.
E)
None of the above.
Ans: A Section: 28.1
24.
Acetylation of serine on prostaglandin synthase leads to the reduction of which lipid mediator?
A)
prostacyclin
B)
thromboxane
C)
prostaglandins
D)
All of the above.
E)
None of the above.
Ans: D Section: 28.2
25.
The function of the enzyme acyl CoA synthetase is
A)
lipolysis to release free glyceraldehyde.
B)
ATP-dependent reduction of acetyl-CoA prior to activation.
C)
ATP-dependent activation of fatty acids using CoA.
D)
All of the above.
E)
None of the above.
Ans: C Section: 28.2
26.
Increasing the activity of adenylate kinase results in the activation of which enzyme?
A)
acetyl CoA carboxylase
B)
cAMP-dependent kinase
C)
PKC
D)
AMP-activated protein kinase
E)
citrate synthase
Ans: D Section: 28.3
Ans: C Section: 28.2
Chapter 28 Fatty Acid Synthesis
4
27.
Which compound inhibits the entry of fatty acyl CoA into the mitochondria as a function of the
cell being in the high-energy state?
A)
malonyl CoA
B)
carnitine acyltransferase
C)
inhibition of acetyl CoA carboxylase
D)
All of the above.
E)
None of the above.
28.
Chronic ethanol ingestion alters carbohydrate metabolism and leads to a fatty liver due to an
increase in which of the following?
A)
NADH
B)
NADPH
C)
ATP
D)
AMP
E)
None of the above.
Ans: A Section: 28.4
29.
Insulin leads to
A)
an activation of fatty acid synthesis.
B)
an inhibition of fatty acid synthesis.
C)
a phosphorylation of proteins.
D)
a decrease of protein phosphatase hydrolysis of fatty acid synthesis enzymes.
E)
a decrease in pyruvate transport into mitochondria.
Ans: A Section: 28.4
30.
What enzyme catalyzes the committed step in fatty acid synthesis?
A)
enoyl reductase
B)
acetyl CoA carboxylase
C)
transacylase reductase
D)
3-hydroxyacyl dehydratase
E)
None of the above.
Ans: B Section: 28.1
31.
Enzymes from which of the following pathways are utilized for fatty acid synthesis?
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: 28.1
32.
Acetyl carboxylaseis is regulated globally by
A)
allosteric inhibitors and activators.
B)
phosphorylation and dephosphorylation.
C)
zymogen activation.
D)
the binding of cAMP.
E)
None of the above.
Ans: B Section: 28.3
Ans: A Section: 28.3
Chapter 28 Fatty Acid Synthesis
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33.
How are fatty acids larger than the 16 carbons formed?
A)
by elongation reactions catalyzed by enzymes on the endoplasmic reticulum
B)
by 1-carbon additions at the mitochondrial membrane
C)
by elongation reactions catalyzed by enzymes in the peroxisomes
D)
All of the above.
E)
None of the above.
34.
Aspirin binds and blocks which of the following enzymes, thus explaining its multiple effects?
A)
phospholipase A2
B)
prostacyclin synthase
C)
diaceylglycerol lipase
D)
thromboxane synthase
E)
prostaglandin synthase
Ans: E Section: 28.2
35.
How are the consumption of eating corn oil and prostaglandin synthesis related?
A)
Prostaglandins are synthesized from membrane proteins originally derived from corn oil.
B)
ω-six fatty acids found in corn oil inhibit thromboxane synthase, shifting synthesis to
prostaglandins.
C)
Corn oil contains linoleate, required for arachidonate synthesis.
D)
ω-three fatty acids found in corn oil inhibit thromboxane synthase, shifting synthesis to
prostaglandins.
E)
Prostaglandidn synthesis and corn oil are not related.
Ans: C Section: 28.2
36.
How does the cell ensure that fats are not synthesized when the energy charge of the cell is low?
A)
Acetyl CoA carboxylase 1 is switched off by phosphorylation.
B)
AMP-activated protein kinase is activated by AMP.
C)
Acetyl CoA carboxylase 1 exists as inactive dimers unless citrate and ATP levels are
high.
D)
Polymerization of active acetyl CoA carboxylase I is facilitated by the protein MIG12.
E)
All of the above.
Ans: E Section: 28.3
37.
Fatty acid synthesis is regulated by hormone depending on feeding vs. fasting and recent
exercise vs. no recent exercise. Which hormones are active and what is their mechanism of
action of the(se) hormone(s) after exercise and a meal?
A)
Insulin stimulates fatty acid synthesis by activating acetyl CoA carboxylase 1.
B)
Insulin stimulates the mobilization of fatty acids for β oxidation.
C)
Epinephrine stimulates the mobilization of fatty acids and stimulates their accumulation
as triacylglycerols.
D)
Glucagon activates the carboxylase by enhancing the phosphorylation of AMPK.
E)
Epinephrine stimulates AMPK, preventing the phosphorylation of acetyl CoA
carboxylase 1.
Ans: A Section: 28.4
Ans: A Section: 28.2
Chapter 28 Fatty Acid Synthesis
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38.
What are the conditions that lead to a “beer gut” due to the excess consumption of alcohol?
A)
NADH produced from the metabolism of ethanol stimulates the citric acid cycle for
glucose-derived acetyl CoA.
B)
Excess ethanol metabolism leads to an accumulation of NADH that inhibits fatty acid
metabolism.
C)
NADH stimulates citric acid cycle enzymes that stimulates glucose-derived acetyl CoA
metabolism.
D)
NADH inhibits ketone body formation, stimulating glucose rather than fatty acid
metabolism.
E)
The processing of acetate in the liver becomes inefficient leading to a pH imbalance in
liver cells, reducing enzyme efficiency in general.
Short-Answer Questions
39.
What are the four physiological roles for fatty acids?
modification of proteins via covalent lipid attachment, (3) as fuel molecules, and (4) as
precursors of hormones and messengers.
Section: Introduction
40.
What are the similarities between fatty acid synthesis and degradation?
Ans:
The processes are very similar, only in reverse directions. The intermediates are
structurally similar and the steps are in similar order.
Section: 28.1.
41.
Describe the chemistry for fatty acid synthesis at the stage when a two-carbon molecule reacts
with a three-carbon molecule to give a four-carbon molecule and a 1-carbon molecule.
Ans:
This is the activation and condensation of malonyl CoA and acetyl CoA. The loss of a
Section: 28.1
42.
What is citrate’s role in fatty acid synthesis?
reaction, making acetyl CoA available for fatty acid synthesis. Thus, citrate is the acetyl
group carrier from the mitochondria to the cytoplasm.
Section: 28.1
43.
NADPH-reducing equivalents important for the biosynthesis of fatty acids come from several
sources. Explain.
into the cytosol. The additional reducing equivalents come from the pentose phosphate
pathway, one of the main products of the pathway.
Section: 28.1
Ans: B Section: 28.4
Chapter 28 Fatty Acid Synthesis
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44.
How is the structure of fatty acid degradation enzymes different from that of synthesis enzymes?
45.
Describe the regulation of fatty acid synthesis by AMP and citrate.
by allosteric mechanism.
Section: 28.2
46.
Where are the enzymes for fatty acid elongation and desaturation in eukaryotes?
on the cytoplasmic surface of the endoplasmic reticulum.
47.
Why are linoleate (18:2) and linolenate (18:3) considered essential fatty acids in mammals?
be consumed in the diet.
Section: 28.2
48.
Describe the allosteric stimulatory effect of citrate on acetyl CoA carboxylase.
polymerization of these dimers into the active filamentous form.
Section: 28.3
49.
In fatty acid synthesis, what is the compound X in the following metabolic conversion?
CH3(CH2)2CCH2C SACP
OO
X
Section: 28.1
50.
Explain this statement: “Fats burn in the flame of carbohydrates.”
cycle. It is diverted to a different pathway.
enzyme complex. This makes the process more efficient.