BIOD53H3 : Biochem

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chocolatellama223

5 Jul 2011

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The acetyl coa that enters the citric cycle is not the one that leaves as co2. Pyruvate dehydrogenase and other dehydrogenases are multiprotein complexes-decarboxylate the carbon chain using the decarboxylation energy to drive other reactions fwd enery requiring step: addition of coenzyme a. Two decarboxylation reactions. --> full oxidation of glucose; 2 c"s leave in form of co2. Mostly energy in form of atp and nadh, these provide electrons to etc. The reason that citric cycle can go fwd are the early reactions they have a very large ve free energy, they provide and pull rxns like citrate synthase forward. Citrate synthase reaction is pulled fwrd and has ve free energy because of the cleavage of the thioester bond , release of coa from acetyl-coameans citrate cycle is always favourable even when reactants are limited. Net actual free energy is neutral is not taking energy or wasting energy to produce nadh. 3 nadh produced /acetyl-coa and in pyruvate dehydrogenase rxn.

Related Questions

CITRIC ACID CYCLE.

1. Briefly describe the biological rationale for each of thefollowing allosteric phenomena: a)activation of pyruvatecarboxylase by acetyl-CoA; b)activation of pyruvate dehydrogenasekinase by NADH; c) inhibition of isocitrate dehydrogenase by NADH;d)activation of isocitrate dehydrogenase by ADP;e)inhibition ofalpha-ketoglutarate dehydrogenase by succinyl-CoA; f) activation ofpyruvate dehydrogenase phosphotase by Ca2+

purplebear480

1. Choose the TWO correct statements describing the citrate cycle.

	ATP is an indirect product of the citric acid cycle
	Acetyl CoA can increase the pool of citric acid cycle intermediates
	Fatty acids can increase the pool of citric acid cycle intermediates
	ADP inhibits Î±-ketoglutarate dehydrogenase
	The pool of mitochondrial oxaloacetate can be increased by pyruvate
	All enzymes of the citric acid cycle are found soluble and free in the mitochondrial matrix

2.Which molecule in the net reaction of the citrate cycle contributes to the inhibition of pyruvate dehydrogenase?

	NADH
	H⁺
	H₂O
	FAD

3. How would a high NADH to NAD⁺ ratio be expected to affect the pyruvate dehydrogenase reaction?

	The E1 subunit is phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase decreases.
	The last step of the pyruvate dehydrogenase reaction is blocked, resulting in a decrease in activity.
	The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate.
	The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an increase in pyruvate dehydrogenase activity.

CITRIC ACID CYCLE.

1. Briefly describe the biological rationale for each of thefollowing allosteric phenomena: a)activation of pyruvatecarboxylase by acetyl-CoA; b)activation of pyruvate dehydrogenase kinase byNADH; c) inhibition ofisocitrate dehydrogenase by NADH; d)activation of isocitrate dehydrogenase byADP; e)inhibition ofalpha-ketoglutarate dehydrogenase by succinyl-CoA;f) activation of pyruvatedehydrogenase phosphotase by Ca2+

2. Predict which one of the 5 steps of the alpha-ketoglutaratedehydrogenase complex reaction is metabolically irreversible underphysiological conditions and explain why?

crimsoncoyote288

BIOD53H3 : Biochem

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