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Biochemistry

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Carbohydrates

Question
24 out of 40
 

Thiamine requirement by body depends on consumption of (AIIMS May 2009)



A Carbohydrates
B Fats

C Amino acids
D Cholesterol

Ans. A Carbohydrates (Ref: Harper, 27th Edition, Page no. 636, 637)

a. Vitamin B1 (thiamine) contains two heterocyclic rings—a pyrimidine ring and a thiazole ring which are joined by a methylene group.

b. The active form of vitamin B1 is thiamine diphosphate(TPP), which contributes as a coenzyme to the transfer of hydroxy alkyl residues (active aldehyde groups).

c. The functional component of TPP is the sulfur- and nitrogen-containing thiazole ring

d. The most important reactions of this type are oxidative decarboxylation of 2-oxoacids and the transketolase reaction in the pentose phosphate pathway.

I. The oxoacid dehydrogenases include

a. the pyruvate dehydrogenase complex (PDH, pyruvate acetyl CoA),

b. the 2-oxoglutarate dehydrogenase complex of the tricarboxylic acid cycle (ODH, 2-oxoglutarate succinyl CoA),

c. the branched chain dehydrogenase complex, which is involved in the catabolism of valine, leucine, and isoleucine

II. Transketolase,which contains thiamine diphosphate, transfers C2 fragments from one sugar phosphate to another. The reactions in the regenerative segment of the PPP are freely reversible. It is therefore easily possible to use the regenerative part of the pathway to convert hexose phosphates into pentose phosphates. This can occur when there is a high demand for pentose phosphates—e. g., during DNA replication in the S phase of the cell cycle

Vitamin B1 deficiency leads to beriberi, a disease with symptoms that include neurological disturbances, cardiac insufficiency, and muscular atrophy

Carbohydrates Flashcard List

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