Tuesday, January 8, 2008

6 - biochemistry mcqs - 41 to 53 - citric acid cycle

41 - the most crucial regulators of the citric acid cycle are its substrates , acetyl co A and oxaloacetate , and its product , NADH .

the above statement is true .


42 - which enzyme of the citric acid cycle is very similar structurally and mechanistically to lactate dehydrogenase and alcohol dehydrogenase ?

a- alpha ketoglutarate dehydrogenase
b- succinate dehydrogenase
c- NAD + dependent isocitrate dehydrogenase
d- malate dehydrogenase

answer is d .


43 - the thiamine pyrophosphate ( TPP ) a cofactor is bound to E1 and decarboxylates pyruvate , yielding a hydroxyethyl TPP carbon ion .

the above statement is true .


44 - several biosynthetic pathways use citric acid cycle intermediates as starting material for anabolic reactions .

the above statement is true .


45 - lipoamide consists of lipoic acid covalently joined to the epsilon - amino group of a lysine residue via an amide bond .

the above statement is true .


46 - how is flux through out the citric acid controlled ?

a- primarily by control of citrate synthase
b- primarily by control of isocitrate dehydrogenase
c- primarily by control of alpha ketoglutarate dehydrogenase
d- at many points , including all the above

answer is d .


47 - alpha ketoglutarate dehydrogenase is a multienzyme complex containing alpha ketoglutarate dehydrogenase ( E 1 ) , dihydro lipoyl trans succinylase ( E2 ) and dihydro lipoyl dehydrogenase .

the above statement is true .


48 - in pyruvate dehydrogenase which cofactor is used to decarboxylate pyruvate?

a- TPP
b- lipoic acid
c- co A
d- FAD

the answer is a .


49 - describe the regulatio of the conversion of isocitrate to alpha keto glutarate ?

a- calcium and ADP stimulate , NADH AND ATP inhibit .


50 - Isocitrate lyase and malate sythase occur in both plants and animals .

the above statement is false . these enzymes occur only in plants .


51 - acetyl co A is formed from pyruvate through oxidative decarboxylation by a multienzyme complex named ?

answer is pyruvate dehydrogenase .


52 - which three compounds associated with the citric acid cycle inhibit their own synthesis ?

answer is acetyl co A , citrate and succinyl co A .


53 - the tight coupling of oxygen consumption , NADH reoxidation and ATP production in the citric acid cycle requires regulation by feedback mechanisms that coordinate NADH Production with energy expenditure .



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