Question

The citric acid cycle and oxidative phosphorylation take place in the mitochondrion, a highly compartmentalized organelle. What is the role of this compartmentalization in these processes and why is it essential to their function? Discuss using thermodynamic terms. Could these processes occur in the cytoplasm?

Answer 1

all reactions in the cell take place in certain specific sites or compartments of the cells. compartmentalization provides separation of an activity or process from other cellular processes and large surface area for the process to take place. compartmentalization results due to the presence of specific membranes inside the cell.

In the mitochondrion, compartmentalization provides a large surface area that enhances the productivity of the mitochondrion and the separation of the TCA cycle from oxidative phosphorylation. TCA cycle takes place in the mitochondrial matrix and oxidative phosphorylation takes place from inner mitochodrial membrane to matrix.

During TCA cycle, the electrons from Acetyl-CoA are removed and are used to reduce NAD+ and FAD+. In TCA cycle one GTP is formed via substrate-level phosphorylation. The NADH2 and FADH2 are passed onto a set of membrane-bound enzymes in the mitochondrion. These set of membrane-bound enzymes together is known as oxidative phosphorylation. The electrons of NADH and FADH2 provide energy for the movement of positively charged protons across the mitochondrial inner membrane.

The NADH and FADH2 convey their electrons to the electron transport chain, which contains number of proteins located in the inner membrane of the mitochondrion. The step-wise movement of electron from one protein to another in the ETC, indicates the overall decrease in the amount of energy of the electron. oxygen acts as a terminal electron acceptor in the ETC, where there is a maximal amount of free energy is released.

For every molecule of acetylCoA entered in the TCA cycle, there is a net gain of 3 NADH, 1 FADH2 and 1 ATP. when the electrons are moving down the concentration gradient, protons will accumulate at the other side of the inner mitochondrial membrane. As the protons start moving back into the mitochondrial matrix, the resulting energy is used to synthesize the ATP.