Question

(A) For the following reaction identify:

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i the electron donor

ii the electron acceptor

iii all redox pairs

iv reducing agents

v oxidizing agent

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Succinate + FAD+ <--> Fumarate + FADH2

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(B) Why could less ATP produced from NADH from glycolysis than NADH from the citric acid cycle?

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(C) What role does succinate dehydrogenase play in oxidative phosphorylation?

Answer 1

Succinate + FAD+ <--> Fumarate + FADH2

Q1) ​In this biochemical reaction succinate gets oxidized to fumarate whereas FAD+ gets reduced to FADH2.

Here

i) electron donor = Succinate

ii) electron acceptor = FAD+

iii) All redox pairs: Succinate/Fumarate, FAD+/FADH2

iv) Reducing agent: Succinate

v) Oxidizing agent:  FAD+

Q2) NADH from glycolysis enters the Electron Transport chain at complex II (Succinate dehydrogenase) via Flavoproteins and drive the transport of only 6 protons across the inner mitochondrial membrane. The backflow of 3 protons through the proton channel of ATP synthase drive the synthesis of 1 ATP molecule. hence the cytoplasmic NADH produces 1.5 - 2 ATP molecules. However the mitochondrial NADH joins the ETC at complex I (NADH-dehydrogenase complex) which drive the transport of 10 protons across the inner mitochondrial membrane sufficient to produce 2.5 to 3 ATP molecules.

Q3) Succinate dehydrogenase is the enzyme involved in the oxidation of succinate to Fumarate. The enzyme has FAD+ as the coenzyme which gets reduced to FADH2. FADH2 then reduces the ETC components at complex II (Ubiquinone) and ultimately drives the synthesis of 1.5 -2 ATP molecules/FADH2 molecule. Succinate dehydrogenase provides an electron donor which donates electrons to different ETC components and ultimately to Oxygen for terminal oxidation.

Thank you