Regulation of Fatty Acid Synthesis

Regulation of Fatty Acid Synthesis

Q. 1 A newborn infant has severe respiratory problems. Over the next few days, it is observed that the baby has severe muscle problems, demonstrates little development, and has neurological problems. A  liver  biopsy reveals a very low level of acetyl CoA carboxylase, but normal levels of the enzymes of glycolysis, gluconeogenesis, the citric acid cycle, and the pentose phosphate pathway. What is the most likely cause of the infant’s respiratory problems?
 A Low levels of phosphatidyl choline
 B Biotin deficiency
 C Ketoacidosis
 D High levels of citrate
Q. 1 A newborn infant has severe respiratory problems. Over the next few days, it is observed that the baby has severe muscle problems, demonstrates little development, and has neurological problems. A  liver  biopsy reveals a very low level of acetyl CoA carboxylase, but normal levels of the enzymes of glycolysis, gluconeogenesis, the citric acid cycle, and the pentose phosphate pathway. What is the most likely cause of the infant’s respiratory problems?
 A Low levels of phosphatidyl choline
 B Biotin deficiency
 C Ketoacidosis
 D High levels of citrate
Ans. A

Explanation:

Acetyl CoA carboxylase deficiency drastically alters the ability of the patient to synthesize fatty acids. The fact that the infant was born at all is due to the body’s ability to utilize fatty acids provided to it. However, all processes dependent  upon  de  novo  fatty  acid  biosynthesis  are  affected.  The  lungs,  in  particular,  require  surfactant,  a lipoprotein substance secreted by alveolar type II cells, to function properly. Surfactant lowers alveolar surface tension, facilitating gas exchange. It contains significant amounts of dipalmitoyl phosphatidylcholine. Palmitate is the major end product of de novo fatty acid synthesis. Acetyl CoA carboxylase formation of malonyl CoA is the first step of fatty acid synthesis. Biotin deficiency cannot be the problem because pyruvate carboxylase in gluconeogenesis is not affected. None of the other answers listed would result in all of the symptoms given.


Q. 2 Allosteric activator of Acetyl CoA carboxylase:
 A Malonyl CoA
 B Acetyl CoA
 C Citrate
 D Biotin
Q. 2 Allosteric activator of Acetyl CoA carboxylase:
 A Malonyl CoA
 B Acetyl CoA
 C Citrate
 D Biotin
Ans. C

Explanation:

Citrate


Q. 3

Which among the following is the allosteric activator of acetyl CoA carboxylase?

 A

Malonyl CoA

 B

Acetyl CoA

 C

Citrate

 D

Biotin

Q. 3

Which among the following is the allosteric activator of acetyl CoA carboxylase?

 A

Malonyl CoA

 B

Acetyl CoA

 C

Citrate

 D

Biotin

Ans. C

Explanation:

Acetyl-CoA carboxylase is an allosteric enzyme and is activated by citrate, which increases in concentration in the well-fed state and is an indicator of a plentiful supply of acetyl-CoA. Citrate promotes the conversion of the enzyme from an inactive dimer to an active polymeric form, with a molecular mass of several million.
 
Ref: Botham K.M., Mayes P.A. (2011). Chapter 23. Biosynthesis of Fatty Acids & Eicosanoids. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.  

 

Quiz In Between


Q. 4

Acetyl CoA carboxylase requires which vitamin for function:

 A

Thiamin

 B

Riboflavin

 C

Biotin

 D

Niacin

Q. 4

Acetyl CoA carboxylase requires which vitamin for function:

 A

Thiamin

 B

Riboflavin

 C

Biotin

 D

Niacin

Ans. C

Explanation:

Bicarbonate as a source of CO2 is required in the initial reaction for the carboxylation of acetyl-CoA to malonyl-CoA in the presence of ATP and acetyl-CoA carboxylase.
Acetyl-CoA carboxylase has a requirement for the B vitamin biotin. The enzyme is a multienzyme protein containing a variable number of identical subunits, each containing biotin, biotin carboxylase, biotin carboxyl carrier protein, and transcarboxylase, as well as a regulatory allosteric site.
Ref: Harper 28th edition, chapter 23.

Q. 5

Acetyl CoA carboxylase enzyme is present in ‑

 A

Cytosol

 B

Mitochondria

 C

Nucleus

 D

Lysosome

Q. 5

Acetyl CoA carboxylase enzyme is present in ‑

 A

Cytosol

 B

Mitochondria

 C

Nucleus

 D

Lysosome

Ans. A

Explanation:

Ans. is ‘a’ i.e., Cytosol

This question is slightly different from previous one.

The major acetyl CoA carboxylase which is involved in lipogenesis is acetyl CoA Carboxylase-1 (ACC-1). It is a cytosolic enzyme. In general acetyl CoA carboxylase refers to ACC-1.

There is one more isoform of acetyl CoA carboxylase, i.e. ACC-2. Which is present in muscle, allowing muscle to regulate β-oxidation. ACC-2 is present in mitochondria.

Quiz In Between



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