Chapter 29 Lipid 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) liver
b) receptor-mediated endocytosis
c) phosphatidyl ethanolamine
d) muscle
e) lipoprotein particles
f) dihydroxyacetone phosphate
g) vitamin D
h) pregnenolone
i) glycocholate
j) acetyl CoA
k) vitamin A
l) sphingomyelin
1.
In mammals, the _______________ is the major site of triacylglycerol synthesis.
2.
The reduction of the metabolite _______________ supplies glycerol 3-phosphate for
acylglycerol synthesis.
Ans:
f
Section: 29.1
3.
The membrane component _______________ is produced from the activated precursor CDP-
diacylglycerol.
Ans:
c
Section: 29.1
4.
_______________ is a component of the myelin sheath.
Ans:
l
Section: 29.1
5.
All of the carbons in cholesterol are derived from the metabolite _______________.
Section: 29.2
6.
_______________ is the process by which LDL enters the cell.
Ans:
b
Section: 29.4
7.
Cholesterol and triacylglycerols are transported in body fluids in the form of _______________.
Ans:
e
Section: 29.4
Ans:
a
Section: 29.1
Chapter 29 Lipid Synthesis
2
8.
_______________ is the vitamin that is a derivative of cholesterol.
9.
_______________ is the primary bile salt.
Ans:
i
Section: 29.4
10.
_______________ is the derivative of cholesterol that is the precursor of the steroid hormones.
Ans:
h
Section: 29.5
Fill–in-the-Blank Questions
11.
In mammalian cells, phosphatidate is synthesized in the outer mitochondrial membrane and the
_____.
Ans: endoplasmic reticulum Section: 29.1
12.
A(n) ____ is composed of a fatty acid linked to sphingosine via an amide bond.
Ans: ceramide Section: 29.1
13.
In the biosynthesis of phosphatidates, the fatty acyl group attached to the C-2 position is usually
_____.
Ans: unsaturated Section: 29.1
14.
_____ is a nine-carbon sugar that is a component of the gangliosides.
Ans: Sialic acid or N-acetylneuraminic acid Section: 29.1
15.
In the biosynthesis of sphingomyelin, the terminal hydroxyl group of ceramide is substituted
with ______.
Ans: phosphorylcholine Section: 29.1
16.
In membrane-lipid biosynthesis, the nucleotide _____ is used to activate the components of the
reaction.
Ans: cytidine triphosphate (CTP) Section: 29.1
17.
The synthesis of _____ is the committed step in cholesterol biosynthesis.
Ans: mevalonate Section: 29.2
18.
_____ is the 30-carbon (triterpene) precursor of cholesterol.
Ans: Squalene Section: 29.2
19.
_____ is the major carrier of cholesterol esters in the blood.
Ans: Low-density lipoprotein (LDL) Section: 29.4
20.
Vitamin D3 is converted into _____, which is an active hormone that functions as a transcription
factor.
Ans: calcitriol (1,25-dihydroxycholecalciferol) Section: 29.5
Ans:
g
Section: 29.5
Chapter 29 Lipid Synthesis
3
Multiple-Choice Questions
21.
Which of the following is the common precursor for both the phosphatidyl inositols and
triacylglycerols?
A)
diacylglycerol
B)
inosinic acid
C)
phosphatidate
D)
CDP-diacylglycerol
E)
None of the above.
22.
Phosphatidate is formed from
A)
glycerol 3-phosphate and two fatty acyl CoAs.
B)
glycerol and two free fatty acids.
C)
pyruvate and triacylglycerol.
D)
glycerol and two fatty acyl CoAs.
E)
None of the above.
Ans: A Section: 29.1
23.
In a ganglioside, what links the oligosaccharide to the hydroxyl of the ceramide?
A)
stearic acid
B)
glucose
C)
choline
D)
sialic acid
E)
None of the above.
Ans: B Section: 29.1
24.
The highest concentration of sphingolipids is found in the
A)
central nervous system.
B)
lymph system.
C)
serum.
D)
All of the above.
E)
None of the above.
Ans: A Section: 29.1
25.
The starting materials necessary to synthesize sphingosine are
A)
palmitoyl CoA and serine.
B)
acetyl CoA and glycine.
C)
palmitoyl CoA and aspartate.
D)
acetyl CoA and glutamine.
E)
None of the above.
Ans: A Section: 29.1
26.
Which of the following is(are) major component(s) of low-density lipoproteins?
A)
phospholipid
B)
apoprotein B-100
C)
cholesteryl ester
D)
All of the above.
E)
None of the above.
Ans: D Section: 29.4
Ans: C Section: 29.1
Chapter 29 Lipid Synthesis
4
27.
Respiratory distress syndrome is caused by a failure in the biosynthetic pathway of
A)
sphingosine.
B)
gangliosides.
C)
dipalmitoylphosphatidylcholine.
D)
cholesterol.
E)
bile salts.
28.
Tay Sachs disease is caused by an inability to degrade
A)
sphingosine.
B)
gangliosides.
C)
dipalmitoylphosphatidylcholine.
D)
ceramide.
E)
None of the above.
Ans: B Section: 29.1
29.
HMG CoA is synthesized from acetyl CoA and
A)
oxaloacetate.
B)
acetoacetyl CoA.
C)
acetyl CoA.
D)
farnesyl pyrophosphate.
E)
mevalonate.
Ans: B Section: 29.2
30.
Feedback regulation of cholesterol synthesis is mainly controlled at the step catalyzed by the
enzyme
A)
3-hydroxy-3-methylglutaryl (HMG) CoA reductase.
B)
geranyl transferase.
C)
HMG transferase.
D)
farnesyl reductase.
E)
None of the above.
Ans: A Section: 29.3
31.
The role of lipoprotein particles is to
A)
solubilize hydrophobic lipids.
B)
aid in clot formation.
C)
contain cell-targeting signals.
D)
A and B.
E)
A and C.
Ans: E Section: 29.4
32.
The major carrier(s) of dietary fat from the intestine is(are)
A)
VLDL.
B)
chylomicrons.
C)
HDL.
D)
LDL.
E)
IDL.
Ans: B Section: 29.4
Ans: C Section: 29.1
Chapter 29 Lipid Synthesis
5
33.
The LDL receptors on the plasma membrane are localized in coated pits that contain the
receptors of which of the following proteins?
A)
clathrin
B)
lipoprotein A
C)
adrenodoxin
D)
HMG-CoA reductase
E)
sterol regulatory element binding protein (SREBP)
34.
Which of the following combines with cholic acid to form a major bile salt?
A)
ATP
B)
glycine
C)
glycerol
D)
A and B
E)
A, B, and C
Ans: B Section: 29.5
35.
Hydroxylation of cholesterol by cytochrome P450 requires
A)
NADPH.
B)
activated O2.
C)
PLP.
D)
A and B.
E)
A and C.
Ans: D Section: 29.5
36.
In previous chapters, biosynthetic pathways were commonly regulated by phosphorylation/
dephosphorylation mechanisms. Which of the following mechanisms for steroid biosynthesis
uses an alternative method?
A)
The sterol regulatory element binding protein (SREBP) migrates to the nucleus and binds
the sterol regulatory element (SRE) stimulating transcription.
B)
The SREBP is cleaved from the endoplasmic reticulum membrane rendering it inactive;
thus, it no longer blocks steroid synthesis.
C)
CTP reacts with acetoacetate to provide an activated substrate to start cholesterol
synthesis.
D)
CTP reacts with acetate to provide an activated substrate to start cholesterol synthesis.
E)
CTP is required to provide the phosphate for the conversion of mevalonate to 5-
phosphomevalonate unlike other pathways that use ATP.
Ans: A Section: 29.3
Ans: A Section: 29.4
Chapter 29 Lipid Synthesis
6
37.
Your grandfather has been told he has high cholesterol and has been given one of the statins to
bring it down. He asks you if you can think of any reason that he should not double the dose so
that it will reduce blood cholesterol faster. What do you tell him?
A)
Yes, statins block the reabsorption of bile, effectively blocking the absorption of
cholesterol.
B)
Yes, statins decrease the amount of LDL receptors on the surface of intestinal mucosal
cells, thereby decreasing cholesterol uptake into the blood.
C)
Yes, statins increase the amount of LDL receptors on the surface of blood vessels
increasing the internalization of cholesterol into cells and clearing the blood.
D)
No, at high levels, statins have a stimulatory effect on HMG-CoA reductase rather than
inhibitory effect.
E)
No, some cholesterol synthesis is essential. Cholesterol is essential for proper functioning
of cell membranes and for precursors for bile salts and steroid hormones.
38.
A friend, who is struggling with weight gain, reads about a new miracle supplement that blocks
the formation of phosphatidate, the precursor for triacylglycerols. Would taking this supplement
work as a weight reduction scheme?
A)
Yes, many weight loss drugs target enzyme catalyzed reactions that occur early in this
biosynthetic pathway.
B)
Yes, decreases in phosphatidate leads to activation of key β-oxidation enzymes, which
drives lipid metabolism over glucose metabolism.
C)
Yes, decrease in phosphatidate leads to increases in cellular glycerol 3-phosphate, which
stimulates glycolytic enzymes.
D)
No, because this would also block formation of phospholipids and cell membrane
integrity would be impacted.
E)
No, triacylglycerol synthesis takes place in the mitochondria and it is unlikely that there
is a transporter for the supplement in the inner membrane.
Ans: D Section: 29.1
39.
You are prone to sunburn, but you doctor tells you not to apply your sunscreen until you have
been outside for five minutes. Why?
A)
Sunscreen blocks UV radiation necessary for cholesterol synthesis in the skin where it is
converted to vitamin D.
B)
Sunlight is necessary for the conversion of cholesterol to vitamin D, a hormone
necessary for bone health.
C)
Skin pigmentation, as occurs when you get a light tan, blocks UV radiation and reduces
the incidence of skin cancers.
D)
Vitamin D in the skin blocks UV radiation, but only for a short period of time; thus, it is
a natural sun block.
E)
Sunlight promotes HDL mobilization and a clearing of cholesterol in the blood.
Ans: B Section: 29.5
Ans: E Section: 29.4
Chapter 29 Lipid Synthesis
7
40.
If you were considering designing a drug to regulate blood pressure, which of the following
families of steroids would you target?
A)
androgens
B)
estrogens
C)
glucocorticoids
D)
mineralocorticoids
E)
progestogens
Short-Answer Questions
41.
What are the causes and symptoms of familial hypercholesterolemia?
This disease is caused by a deficiency of the LDL receptor.
Section: 29.4
42.
How is methionine metabolism related to the synthesis of phosphatidyl choline?
intermediate in methionine metabolism.
Section: 29.1
43.
What is the role of CTP in the synthesis of a phospholipid?
inositol, and cytidine monophosphate (CMP) is released.
Section: 29.1
44.
Why is phosphatidyl serine considered a class of molecules, and not one type?
many different types of phospholipids.
Section: 29.1
45.
What is phosphatidyl choline? How is it synthesized in mammals?
ethanolamine by S-adenosylmethionine.
Section: 29.1
46.
How are gangliosides synthesized?
Section: 29.1
Ans: D Section: 29.5
Chapter 29 Lipid Synthesis
8
47.
What are the three stages of cholesterol synthesis?
48.
What is the role of phosphatidyl choline in the synthesis of sphingomyelin?
group is transferred to ceramide from phosphatidyl choline to form sphingomyelin and a
diacylglycerol.
Section: 29.1
49.
Describe the various ways that 3-hydroxy-3-methylglutaryl CoA reductase is regulated,
including both gene expression and enzyme regulation.
regulated. (4) The enzyme activity is mediated by phosphorylation, as an AMP-activated
protein kinase switches activity off.
Section: 29.3
50.
List the types of lipoprotein particles and give the primary physiological role of the lipoprotein.
Ans:
Chylomicrons
Transport dietary fat
Very-low-density lipoproteins (VLDL)
Transport endogenous fat
Intermediate-density lipoproteins (IDL)
Precursor to LDL
Low-density lipoproteins (LDL)
Transport cholesterol
High-density lipoproteins (HDL)
Reverse transport of cholesterol from tissue
to liver
Section: 29.4
51.
How do blood levels of lipoproteins serve diagnostic purposes?
HDL serves in a protective capacity, shuttling cholesterol from the cells back to the liver
to maintain proper levels. The LDL/HDL ratio should be about 3:5 in humans.
Section: 29.4
52.
What are the steps in LDL uptake into cells?
and reused.
Section: 29.4
Ans:
The stages are: (1) the synthesis of the isoprene units (isopentyl pyrophosphate), (2)
condensation of six units to form squalene, and (3) cyclization of the squalene.
Section: 29.2
Chapter 29 Lipid Synthesis
9
53.
What are some of the medical strategies to control cholesterol levels at an appropriate level?
54.
What are bile salts?
absorption. Bile salts are components of bile, which is stored in the gall bladder.
Section: 29.5
55.
The first step in vitamin D synthesis is unusual. What is it?
steps to vitamin D.
Section: 29.5
hypercholesterolemia.
Section: 29.3