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Example Questions
Example Question #91 : Anabolic Pathways And Synthesis
The enzyme Acyl-Carrier Protein (ACP) plays an important role in the biosynthesis of which of the following?
Carbohydrates
Lipids
Nucleic Acids
Proteins
Lipids
Acyl-Carrier Protein (ACP) is a protein that is important to the generation of lipids. Specifically, it aids in the production of fatty acids. Furthermore, ACP is just one component of the Fatty Acid Synthase enzyme, which is devoted to the synthesis of fatty acids.
To begin the process, ACP is first activated by having an acetyl-CoA molecule attached to it. Next, a compound called malonyl-CoA is attached to the bound acetyl-CoA. Malonyl-CoA is a three carbon compound, but upon being added to the acetyl-CoA, the malonyl-CoA becomes decarboxylated. The importance of this is that by producing carbon dioxide as a product, this helps to greatly drive the reaction forward.
Keep in mind that there are other chemical transformations happening when these malonyl-CoA molecules are being "stitched" together. Every time a malonyl-CoA is added, the carbon chain becomes increased by two more carbons. This keeps happening until, finally, a fatty acid is generated.
Example Question #92 : Anabolic Pathways And Synthesis
What is the role of lecithin-cholesterol acyltransferase (LCAT) in cholesterol metabolism and transport in the body?
LCAT is an enzyme that incorporates acetyl-CoA into fatty acids
LCAT produces cholesterol esters from cholesterol, which are transported from the peripheral tissues to the liver
LCAT is an enzyme that hydrolyzes fatty acids from triglycerides and cholesterol
LCAT does not impact cholesterol transport
LCAT is an enzyme that converts malonyl-CoA into palmitate
LCAT produces cholesterol esters from cholesterol, which are transported from the peripheral tissues to the liver
Lecithin-cholesterol acyltransferase-LCAT adds a fatty acid to cholesterol, which can then be loaded onto high-density lipoproteins. Without the enzyme, cholesterol does not get to be transported by high density lipoproteins to the liver. Cholesterol then accumulates in tissue such as the eye and renal tissue. LCAT does impact cholesterol transport. Lipoprotein lipase is the enzyme that hydrolyzes fatty acids from triglycerides and cholesterol. Fatty acid synthase converts malonyl-CoA into palmitate. Acetyl-CoA carboxylase is the enzyme that incorporates acetyl-CoA into fatty acids.
Example Question #1 : Lipid Synthesis Enzymes
Which of the following are true about fatty acid desaturase and lipid metabolism?
I. The enzyme is located in the endoplasmic reticulum.
II. The enzyme converts saturated fatty acids to unsaturated fatty acids.
III. The enzyme creates double bonds in fatty acid chains.
IV. The enzyme is important in production of arachidonic acid, an inflammatory pathway and cellular signal intermediate.
I, III, and IV
I, II, and III
I and IV
I, II, III, and IV
I and II
I, II, III, and IV
Fatty acid desaturases are located on the endoplasmic reticulum and convert saturated fatty acids to unsaturated fatty acids by producing double bonds. The enzymes have a N-terminal cytochrome b5-like domain. Arachidonic acid is a highly unsaturated fatty acid.
Example Question #4 : Lipid Synthesis
What is the role of citrate lyase in fatty acid synthesis?
I. It catalyzes the formation of acetyl-CoA and oxaloacetate from citrate and coenzyme A.
II. It converts ATP to ADP and phosphate.
III. It converts ADP to ATP.
IV. It catalyzes the formation of citrate and coenzyme A from acetyl-CoA and oxaloacetate.
I and IV
I and II
I, III, and IV
I only
II, III, and IV
I and II
Citrate crosses the mitochondrial matrix into the cytosol and is converted into acetyl-CoA and oxaloacetate by citrate lyase during fatty acid synthesis, as part of the citrate shuttle. The process requires hydrolysis of energy-rich ATP bonds.
Example Question #1224 : Biochemistry
Which of the following are fatty acid synthase components?
I. Malonyl CoA-ACP transacetylase.
II. Beta-ketoacyl synthase.
III. Beta-ketoacyl reductase.
IV. Acetyl CoA-ACP transacetylase.
Note: acyl carrier protein = ACP
I and II
I, II, III and IV
I and IV
III and IV
I, II, and III
I, II, III and IV
The role of fatty acid synthase is to synthesize fatty acids,more specifically to convert acetyl-CoA, malonyl-CoA, and NADPH to palmitate (a fatty acid) and NADP. It is a multienzyme complex consisting of 7 components: acetyl CoA-ACP transacetylase, malonyl-CoA-ACP transacetylase, Beta-ketoacyl synthase, Beta-ketoacyl reductase, Beta-hydroxyacyl dehydratase, enoyl reductase, thioesterase.
Example Question #93 : Anabolic Pathways And Synthesis
Which statement about fatty acids is false?
Carnitine transports fatty acids into the mitochondrial matrix
Fatty acids are aliphatic
None of the other answers is false
Fatty acid synthesis takes place in the mitochondria
Beta-oxidation 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 #91 : Anabolic Pathways And Synthesis
Which of the following are true?
The pentose pathway produces a coenzyme that is needed for fatty acid degradation
Only one malonyl-CoA molecule is required for palmitate synthesis from acetyl-CoA
Palmitic acid is the precursor of stearic acid
is synthesized during ketogenesis
None of the other answers are true
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 #1231 : Biochemistry
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 mevalonate
Decreasing the production of acetyl-CoA
Increasing the production of malonyl-CoA
Decreasing the production of HMG-CoA
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 #1232 : Biochemistry
What molecule is the source for all of the carbons in cholesterol?
Malonyl-CoA
Acetoacetic acid
Pyruvate
Acetyl-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.