How many NADH.H+ are formed from pyruvic acid during aerobic respiration?

Question

How many NADH.H+ are formed from pyruvic acid during aerobic respiration? (A) Two (B) Three (C) Four (D) Five

Tardigrade Admin · Accepted Answer

Link reaction: If sufficient oxygen is available, each 3-carbon pyruvate molecule enters the mitochondrial matrix where its oxidation is completed by aerobic means. It is called a gateway step or link reaction between glycolysis and Kreb's cycle. Acetyl CoA is a common intermediate of fat and carbohydrate metabolism. Later, this acetyl CoA from both the sources enters the TCA cycle. Link reaction also called oxidative decarboxylation reaction is not a part of Kreb's cycle.

P yr uv a t e + C o A + N A D^{+} \to_{M g^{+ 2}, TPP, L i p o i c a c i d}^{P yr uv a t e d e h y d ro g e na se} A ce t y lC o A + N A D H_{2} + C O_{2}

Kreb's cycle / TCA cycle:
Discovery: This cycle has been named after Sir Hans Kreb, the German biochemist who discovered this cycle in 1937. Kreb's cycle is also known as the citric acid cycle as it is the first stable product of the cycle. This cycle takes place in the matrix of mitochondria as it has the presence of various soluble enzymes here. Like glycolysis, it also involves 10 sequential steps in which the cycle is completed.
Steps producing NADH + H⁺/ NADH₂:
(a) Dehydrogenation-I reaction: In this reaction, oxalosuccinate is formed by dehydrogenation of isocitrate in the presence of enzyme isocitrate dehydrogenase, producing a molecule of NADH₂.

I soc i t r a t e + N A D^{+} \to_{M n^{+ 2}}^{I soc i t r a t e d e h y d ro g e na se} O x a l os u cc ina t e + N A D H_{2}

(b) Oxidative decarboxylation: This reaction is similar to a link reaction. In this reaction,

α -

ketoglutarate in the presence of thiamine pyrophosphate and lipoic acid present in the enzyme complex

α -

ketoglutarate dehydrogenase carries out simultaneous oxidation and decarboxylation in the presence of CoA to produce succinyl CoA. It also produces a molecule of NADH₂.

α - Ke t o g l u t a r a t e + C o A + N A D^{+} \to_{M g^{+ 2}, TPP, L i p o i c a c i d}^{α - Ke t o g l u t a r a t e d e h y d ro g e na se} S u cc in y lC o A + N A D H_{2} + C O_{2}

(c) Dehydrogenation-IV reaction: In this reaction, oxaloacetate is formed by dehydrogenation of malate in the presence of enzyme malate dehydrogenase, producing a molecule of NADH₂.

M a l a t e + N A D^{+} \to M a l a t e d e h y d ro g e na se O x a l o a ce t a t e + N A D H_{2}

Q. How many NADH.H+ are formed from pyruvic acid during aerobic respiration?

Two

Three

Four

Five

Q. How many NADH.H⁺ are formed from pyruvic acid during aerobic respiration?