Question

Answer any one and only one of the following: 

a. Describe the mitochondrial electron transport pathway and the synthesis of ATP by mammalian mitochondria. 

b. Provide an overview of fatty acid synthesis and breakdown and their coordinated regulation. 

c. Discuss the regulation of the TCA cycle. 

d. Compare and contrast the KNF and MWC models. 

Answer 1

NADH₂ & FADH₂ obtained from glycolysis and Kreb's cycle enter in electron transport chain (ETC) and
form H₂O by oxidation.

In this process, energy is released which is used for the synthesis of ATP.

Transfer of electrons from NADH₂ or FADH₂ occurs through a chain of electron acceptors and donors
arranged in a specific sequence.

Electron transport chain is located in inner mitochondrial membrane in Eukaryotes (mammals).

ETS (Respiratory chain) consists of four components

1. FP (flavoprotein) or FMN

2. Fe-S Protein

3. Co-Q

4. Cytochromes.

Cytochromes are cyt.-b, cyt.-C1 & cyt. C, cyt.-a & cyt a3 (cyt a & a3 - Cu containing)

Two electron acceptors coenzyme Q or ubiquinone and cytochrome C can be easily separated from
respiratory chain, therefore they are called mobile carriers. CoQ functions for electon transport between
complex I and III and cyt.C transports electrons between complex III and IV.

Hydrogen is transferred from NADH₂ to FMN and NAD is obtained back from NADH₂. FMN forms
FMNH₂.

Two protons and electrons are released from FMNH₂. Two protons are transported out through
membrane and two electrons are taken up by Fe-S protein.

Terminal oxidation of reduced coenzyme FADH₂ also occurs at mitochondrial ETS. FADH₂ gives its
electron and hydrogen to CoQ and become FAD.

During the ETS, NADH₂ gives itís 2electrons / 2H⁺ to FMN in respiratory chain, thus 3 ATP are generated,
while FADH₂ give its 2electrons / 2H⁺ to CoQ hence only 2 ATP are formed during the process of oxidative
phosphorylation.

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