Question

Cellular respiration takes place largely within the mitochondria and requires a lot of enzymes that are produced in the cytosol. Explain, briefly, how these cellular respiration enzymes will end up in the mitochondria

Answer 1

Cellular respiration is a process that gives energy from glucose. The first step is the breakdown of glucose by the process of glycolysis, which occurs in the cytoplasm. At the end of glycolysis, 2 molecules of pyruvate is produced, along with two ATPs and two NADH molecules. Next, pyruvate is broken to produce Acetyl CoA, which enters the Citric acid cycle. This cycle occurs in the matrix of the mitochondria. All the enzymes in the citric acid cycle are soluble except succinate dehydrogenase. This enzyme is embedded in the inner membrane of the mitochondria.

The outer membrane of the mitochondria contains porin that can allow proteins upto 10kDa to paa through. However, the inner mitochondrial membrane contains cardiolipin which is impermeable. Transport across this membrane is facilitated by the Tom-Tim complex regulated by a signal sequence. The enzymes intended for the mitochondria are tagged with an N-terminal signal sequence, which is recognized by the TOM (translocase of the outer membrane) complex. The enzyme gets inserted into the complex and interacts with the TIM (translocase of the inner membrane). The enzyme is then translocated into the matrix in a process requiring an electrochemical hydrogen ion gradient across the inner membrane.