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Example Questions
Example Question #1 : Lipid Synthesis Reactants, Intermediates, And Products
Which statement about fatty acids is false?
Beta-oxidation takes place in the mitochondria
Carnitine transports fatty acids into the mitochondrial matrix
None of the other answers is false
Fatty acids are aliphatic
Fatty acid synthesis takes place in the mitochondria
Fatty acid synthesis takes place in the mitochondria
Beta-oxidation is the process by which fatty acid molecules are broken down in the mitochondria to generate acetyl-CoA, which then enters the Krebs cycle. Fatty acids are not aromatic (they do not have aromatic rings), rather they are organized in straight chains of hydrocarbons and are therefore aliphatic. Carnitine transports long-chain acyl groups from fatty acids into the mitochondria (so that they can undergo beta-oxidation). Fatty acid synthesis, however, takes place in the cytosol.
Example Question #1 : Lipid Synthesis Reactants, Intermediates, And Products
Which of the following are true?
Only one malonyl-CoA molecule is required for palmitate synthesis from acetyl-CoA
is synthesized during ketogenesis
Palmitic acid is the precursor of stearic acid
None of the other answers are true
The pentose pathway produces a coenzyme that is needed for fatty acid degradation
Palmitic acid is the precursor of stearic acid
During palmitate synthesis, malonyl-CoA molecules keep on being added to the fatty acid chain, seven malonyl CoA molecules total. Ketogenesis does not involve the synthesis of ; rather, NADH is oxidized to
as
-hydroxybutyrate is formed from acetoacetate. The cofactor produced by the pentose phosphate pathway is NADPH, whereas the
-oxidation-mediated degradation of fatty acids requires
and FAD. Palmitic acid is indeed the precursor of stearic acid, as well as of many other fatty acids.
Example Question #1 : Lipid Synthesis Reactants, Intermediates, And Products
Statins are a class of drugs that act to decrease the levels of LDL in blood. Which of the following could be the mechanism of action of statins?
Decreasing the production of HMG-CoA
Decreasing the production of acetyl-CoA
Increasing the production of malonyl-CoA
Decreasing the production of mevalonate
Decreasing the production of mevalonate
Statins function to decrease the activity of HMG-CoA reductase, an important enzyme in the cholesterol synthesis pathway. This enzyme converts HMG-CoA to mevalonate. This step is the rate-limiting (and irreversible) step in this pathway. Statins inhibit this enzyme; therefore, statins prevent the production of mevalonate and cause an accumulation of HMG-CoA. The HMG-CoA can be converted into acetyl-CoA, which can now be used for many other processes.
Example Question #3 : Lipid Synthesis Reactants, Intermediates, And Products
A researcher is analyzing HMG-CoA. He isolates a region of the cell and observes that the HMG-CoA found in this region participates in the synthesis of ketone bodies. What can you conclude about this location in the cell?
Ribosomes found here to synthesize cytosolic proteins
It is bound by an inner and an outer membrane
It has histones
It has enzymes for degradation of cell debris
It is bound by an inner and an outer membrane
HMG-CoA can be found in two locations: cytosol and mitochondria. In the cytosol, HMG-CoA participates in the production of cholesterol. In mitochondria, it participates in the production of ketone bodies. The question states that ketone bodies are produced; therefore, the researcher must be analyzing the mitochondria. Recall that mitochondria has two membranes: an inner and an outer membrane. Ribosomes in cytosol synthesize cytosolic proteins. The nucleus contains histones, which are proteins that facilitate packaging of DNA molecules. Degradative enzymes are found in organelles such as lysosomes and peroxisomes. These organelles clean the cell by removing unwanted cell debris.
Example Question #1231 : Biochemistry
What molecule is the source for all of the carbons in cholesterol?
Pyruvate
Acetoacetic acid
Acetyl-CoA
Malonyl-CoA
Acetyl-CoA
Cholesterol is synthesized from acetyl-CoA. A cholesterol molecule contains 27 carbons and an acetyl-CoA molecule contains 2 carbons. Cholesterol is synthesized from a total of 18 acetyl-CoA molecules. These 18 molecules undergo reactions that yield a 30 carbon molecule and 6 carbon dioxide molecules (total of 36 carbons). The 30 carbon molecule loses 3 methyl groups and becomes the 27-carbon cholesterol molecule. Malonyl-CoA, acetoacetic acid, and pyruvate are not involved in this pathway.
Example Question #5 : Lipid Synthesis Reactants, Intermediates, And Products
The molecule repeatedly added to the growing carbon chain of an endogenously synthesized fatty acid contains how many carbons?
The molecule which is repeatedly added to a growing fatty acid is malonyl-CoA. Malonyl-CoA is synthesized from acetyl-CoA (two carbons) and (one carbon), and, thus, contains three carbons. Of course, it is important to remember that the
of malonyl-CoA leaves during the reaction with the acyl chain being synthesized.
Example Question #1232 : Biochemistry
Which of the following is true about fatty tissue?
Chylomicrons are secreted by enterocytes
Fatty tissue is composed of lipids, which originate mostly in the liver
The lipoprotein lipase digests chylomicrons, yielding glycerol and triacyglycerides
Adipocytes stock mainly glycerol
Chylomicrons are secreted by enterocytes
Adipocytes stock mainly fatty acids, not glycerol; glycerol produced during triacylglycerol degradation is shuttled through the blood to the liver. Lipase does not digest chylomicrons, but rather triacylglycerol, producing glycerol and fatty acids. The lipids (fatty acids) in fatty tissue mostly originate in our diet, not in our liver. Mammals specifically require certain polyunsaturated fatty acids which they are unable to synthesize, like linoleate; these are known as the essential fatty acids. Chylomicrons are proteins which carry triacylglycerols, cholesterol, and other lipids, obtained by the diet, away from the intestine. Chylomicrons are created in the endoplasmic reticulum of small intestine cells i.e., enterocytes and exoctyosed into lymphatic capillaries.
Example Question #1231 : Biochemistry
In what order does fatty acid synthesis occur?
Reduction, reduction, dehydration, condensation
Condensation, reduction, reduction, cleavage
Oxidation, hydration, oxidation, cleavage
Reduction, condensation, dehydration, reduction
Condensation, reduction, dehydration, reduction
Condensation, reduction, dehydration, reduction
The proper order for fatty acid synthesis is condensation, reduction, dehydration, and reduction once again. This creates an activated acyl group that has been lengthened by two carbons through this anabolic biosynthetic pathway.
Example Question #1233 : Biochemistry
Triglycerides (triacylglycerols) contain three fatty acid molecules and a glycerol molecule. Glycerol-3-phosphate is necessary for triglyceride synthesis. Which of these are the sources of glycerol-3 phosphate in the body?
I. Phosphorylation of glycerol by glycerol kinase in the liver forms glycerol-3 phosphate
II. Glycerol 3-phosphatase reduces dihydroacetone phosphate to glycerol 3-phosphate in the liver and adipose tissue
III. Phosphorylation of glycerol by glycerol kinase in the adipose tissue
I and II
I, II, and III
I and III
I only
II only
I and II
The sources of glycerol-3 phosphate for triglyceride synthesis are glycerol in the liver, but not the adipose tissue (adipose tissue does not have glycerol kinase) and from the conversion of dihydroxyacetone phosphate (obtained in glycolysis) to glycerol-3 phosphatase in liver and adipose tissue. Triglycerides are one of the most important forms of storage of lipids in the body.
Example Question #103 : Anabolic Pathways And Synthesis
Triglycerides and glycerophospholipids are lipids similar in structure. What are some structural and functional characteristics of triglycerides and glycerophospholipids?
Glycerophospholipids contain choline or inositol groups
All of these are correct
Glycerophospholipids are part of the cellular membrane and are sources of second messengers such as diacylglycerol
Triglycerides are a form of storing lipids in the body
Triglycerides are formed by three fatty acids and a glycerol molecule
All of these are correct
Triglycerides are the major form of storing dietary lipids in the body.Triglycerides are composed of three fatty acids and a glycerol molecule. In glycerophospholipids the third fatty acid of a triglyceride particle is replaced by a phosphate group and a choline or inositol group. Choline groups are ammonium salt groups in neurotransmitters or phospholipids on cell membranes. Inositol groups are found in second messengers. Glycerophospholipids are part of the cellular membrane and are sources of second messengers such as diacylglycerol and inositol-3-phosphate.
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