Tuesday, January 8, 2008

4 - biochemistry mcqs - 21 to 30 - citric acid cycle

21 - the enzyme of the citric acid cycle that is inhibited by NADH ?

Answer is citrate synthase .


22 - which citric acid cycle intermediates can be used for the synthesis of amino acids and can be regenerated by the same amino acids ?

a- succinyl co A and succinate
b- succinate and fumarate
c- malate and oxaloacetate
d- alpha ketogluatarate and oxaloacetate .

the correct answer is d . alpha ketoglutarate and oxaloacetate .


23 - what is formed in a second concerted acid - base catalysed step of citrate synthase , in which the acetyl co A enol attacks oxaloacetate ?

answer is citryl co A .


24 - which is the thiamine pyro phosphate requiring enzyme that decarboxylates pyruvate with the formation of a hydroxyethyl - TPP intermediate ?

answer is pyruvate dehydrogenase .


25 - what is the name of the catalytically inactive E2 like protein existing in six copies that may help bind E3 to the complex .

answer is PROTEIN X .


26 - What is the name of the cofactor that is bound to E3 and is reduced by lipoamide?

answer is FAD.


27 - this cofactor accepts the acetyl group from the lipoamide in the pyruvate dehydrogenase complex ?

answer is coenzyme A .


28 - This reaction is catalysed by E 3 , in which an acetyl group is transfered to co A , yielding acetyl co A and dihydrolipoamide E2 .



29 - Oxaloacetate undergoes transamination with alanine to produce what ?

a- glutamate and pyruvate
b- glutamate and alpha keto glutarate
c- aspartate and pyruvate
d- aspartate and alpha ketoglutarate


30 - which enzyme produces the second CO 2 and NADH of the citric acid cycle ?

answer is alpha ketoglutarate dehydrogenase .


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