Question

Question 13 Зpt What will be the phenotype of a mitochondria that has less cristae than normal mitochondria? The mitochondria will produce less NADH but not less FADH2 than normal. It will allow the mitochondria to shrink. The mitochondria will have less oxidative phosphorylation The mitochondria won't be affected. The mitochondria will produce riore water molecules.

Answer 1

Mitochondrion is an organelle with two membranes, outer membrane and inner membrane. The outer membrane covers the organelle and the inner membrane forms folded structures called cristae. These structures greatly increase the surface area of the inner membrane. The outer membrane of mitochondria is permeable to many small molecules and ions, which cross the outer membrane through various channel proteins and enter inter-membrane space. The inner membrane is impermeable to these molecules. It is the site various biochemical reactions including electron transport chain and ATP synthesis through oxidative phosphorylation. Oxidative phosphorylation is the process by which ATP is synthesized by aerobic organisms. The energy generated by the oxidation of carbohydrates, fats and proteins is used to synthesize ATP from ADP by phosphorylation.

All the components of the respiratory chain (Complex I, II, III and IV) and ATP synthase are located on inner mitochondrial membrane. The large surface area of the inner membrane due to highly folded cristae harbors a large number of these protein complexes to carry out sufficient oxidative phosphorylation. The given question discusses about a mitochondria that has less cristae than normal mitochondria. Five options are given to explain the phenotype of such mitochondria. The explanations of the options are:

1. This option states that the mitochondria will produce less NADH, but not less FADH2 than normal. NADH is produced during glycolysis and citric acid cycle. Glycolysis takes place in cytosol and citric acid cycle takes place in mitochondrial matrix. FADH2 is also produced in citric acid cycle in mitochondrial matrix. The production of NADH and FADH2 is not affected by the number of cristae in inner mitochondrial membrane. So, this option does not define the phenotype of the given mitochondria.

2. According to second option, the mitochondria with less cristae will shrink. An organelle shrinks when it loses water or fluid from its matrix. As the number of cristae has no effect on the composition of the mitochondrial matrix, there is no effect on the size of mitochondria. Hence, this option is incorrect.

3. The third option states that the mitochondria that has less cristae will have less oxidative phosphorylation. As discussed above, the inner mitochondrial membrane is the site of ATP synthesis by oxidative phosphorylation. A mitochondrion with less cristae will have less protein complexes associated with electron transport chain and less ATP synthases due to decreased surface area. This leads to decrease in oxidative phosphorylation. So, this option is correct.

4. According to this option, the mitochondria won’t be affected by less cristae. As discussed above, less cristae will decrease the surface area of inner mitochondrial membrane and it will affect all the biochemical reactions taking place on inner membrane. The efficiency of mitochondria to carry out these biochemical reactions will decrease. So, this option is incorrect.

5. According to fifth option, the mitochondria with less cristae will produce more water molecules. Water is produced at the last step of electron transport chain in complex IV. Oxygen acts as final electron acceptor to produce water. When surface area of inner membrane decreases with less cristae, the number of electron transport complexes also decrease. This means that less water molecules is produced. So, this option is incorrect.

With the decrease in cristae, the surface area of inner mitochondrial membrane decreases, which leads to reduction in number of electron transport chain complexes and ATP synthases. So, the mitochondria with less cristae will have less oxidative phosphorylation. The answer is option 3.