Biochemistry : Lipid Synthesis Reactants, Intermediates, and Products
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Example Questions
Example Question #11 : Lipid Synthesis
What is the role of cholesterol ester transfer protein in lipid metabolism?
It is part of chylomicrons
It transfers cholesterol esters between different types of lipoproteins
It is part of of high density lipoproteins
It adds fatty acid groups to cholesterol
It is a receptor on liver cells
It transfers cholesterol esters between different types of lipoproteins
Cholesterol ester transfer protein's role in lipid metabolism involves transferring cholesterol esters or triglycerides between different types of lipoproteins in the blood. It is not part of the lipoprotein particle and is not a receptor but, rather, a protein in the blood. Cholesterol and triglycerides are carried in the blood by lipoproteins, which depending on the amount of protein contained are: chylomicrons, very low density proteins, low-density proteins, intermediate density lipoproteins and high density lipoproteins.
Example Question #21 : Lipid Synthesis
Cholesterol is an important lipid required in membranes and for steroid synthesis. Cholesterol can be synthesized from acetyl-coenzyme A. Which of the following is correct about this process?
3-hydroxy-3 methylglutaryl-CoA reductase (HMG-CoA reductase) converts HMG-CoA to mevalonate
All of these
HMG-CoA reductase is localized in the smooth endoplasmic reticulum and HMG-CoA synthase is in the cytoplasm
3-hydroxy-3 methylglutaryl-CoA synthase (HMG-CoA synthase) converts acetyl-CoA to HMG-CoA
3-hydroxy-3 methylglutaryl-CoA reductase (HMG-CoA reductase) is the rate-limiting enzyme of the de novo cholesterol synthesis
All of these
All the answers are correct and show reactions that are necessary in the process of cholesterol synthesis.Cells receive cholesterol from dietary lipoproteins such as low-density lipoproteins and high-density lipoproteins. However, cholesterol can be synthesized " de novo" by the liver directly from acetyl CoA thru a series of reactions described above. HMG-CoA reductase, the rate-limiting enzyme in the process is stimulated by insulin and inhibited by stain drugs.
Example Question #11 : Lipid Synthesis Reactants, Intermediates, And Products
Where are triglycerides produced in the body and what hormone regulates their production?
I. In the adipose tissue and liver. Their production is regulated by insulin and glucagon.
II. In the blood and liver. Their production is regulated by epinephrine and antidiuretic hormone.
III. In the blood as very-low density lipoproteins and chylomicrons. Their production is regulated by epinephrine and growth hormone.
IV. In the muscle. Their production is regulated by growth hormone.
I only
I and IV
II and III
I and II
III and IV
I only
Triglycerides are produced in the adipose tissue and liver. Their production is regulated by insulin and glucagon. They are not directly regulated by growth factors or antidiuretic hormone (ADH). Also, they are transported in the blood as lipoproteins, but are not produced in the blood.
Example Question #23 : Lipid Synthesis
How can fatty acids be created from glucose?
Glucose can be redirected through the pentose phosphate pathways to create fatty acids.
Acetyl-CoA created from pyruvate can be utilized to create fatty acids.
The ATP created at the end of the electron transport chain can be used directly to synthesize fatty acids chains.
Fatty acids can be created from several of the citric acid cycle's intermediate molecules.
Fatty acids can not be created from glucose, but glucose can be created from fatty acids.
Acetyl-CoA created from pyruvate can be utilized to create fatty acids.
Fatty acid synthesis occurs via the addition of acetyl-CoA carbons to a growing fatty acid chain. And so, in order to create fatty acids from glucose, there must be a link between the two molecules. That connection is the acetyl-CoA that is formed from pyruvate at the end of glycolysis and the pyruvate dehydrogenase complex. However, fatty acids can not create pyruvate, as there are no enzymes capable of this reverse reaction.
Example Question #24 : Lipid Synthesis
Which of the following are true regarding acetyl-CoA carboxylase in fatty acid synthesis?
I. The active form of the enzyme is dephosphorylated.
II. Acetyl-CoA carboxylase converts acetyl-CoA to malonyl-CoA, necessary for fatty acid synthesis.
III. Acetyl-CoA carboxylase is highly expressed in adipose tissue and lactating mammary glands, where fatty acid synthesis is important.
IV. Acetyl-CoA carboxylase is highly expressed in the liver.
II, III, and IV
I and IV
I, II, III, and IV
I and II
I only
I, II, III, and IV
Acetyl-CoA carboxylase is high in adipose tissue, lactating mammary glands and liver where fatty acid synthesis is important. It has two catalytic activities as a biotin carboxylase and carboxytransferase. Acetyl-CoA carboxylase converts acetyl-CoA to malonyl-CoA. Compared to other enzymes that are phosphorylated when active, acetyl-CoA carboxylase needs to be dephosphorylated in order to be active.
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