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Biochemistry

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Carbohydrates

Question
16 out of 40
 

Acetyl CoA can be converted into all of the following except (AIIMS May 2011)



A Glucose
B Fatty acids

C Cholesterol
D Ketone bodies

Ans. A Glucose Ref” Harper’s Biochemistry, 27th Edition, Pg. 132-136

a. Acetyl coenzyme A or acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main function is to convey the carbon atoms within the acetyl group to the citric acid cycle to be oxidized for energy production.

b. In chemical structure, acetyl-CoA is the thioester between coenzyme A (a thiol) and acetic acid (an acyl group carrier). Acetyl-CoA is produced during the second step of aerobic cellular respiration, pyruvate decarboxylation, which occurs in the matrix of the mitochondria. Acetyl-CoA then enters the citric acid cycle.

c. Acetyl-CoA is also an important component in the biogenic synthesis of the neurotransmitter acetylcholine. Choline, in combination with acetyl-CoA, is catalyzed by the enzyme choline acetyltransferase to produce acetylcholine and a coenzyme a byproduct.

d. In animals, acetyl-CoA is essential to the balance between carbohydrate metabolism and fat metabolism. In normal circumstances, acetyl-CoA from fatty acid metabolism feeds into the citric acid cycle, contributing to the cell's energy supply.

e. In the liver, when levels of circulating fatty acids are high, the production of acetyl-CoA from fat breakdown exceeds the cellular energy requirements. To make use of the energy available from the excess acetyl-CoA, ketone bodies are produced, which can then circulate in the blood..

f. In some circumstances, this can lead to the presence of very high levels of ketone bodies in the blood, a condition called ketosis. Benign dietary ketosis can safely occur in people following low-carbohydrate diets, which cause fats to be metabolised as a major source of energy. This is different from ketosis brought on as a result of starvation, and from ketoacidosis, a dangerous condition that can affect diabetics.

g. Because of irreversible nature of pyruvate dehydrogenase complex, acetyl CoA cannot be converted to pyruvate and therefore glucose cannot be synthesized

Carbohydrates Flashcard List

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