Question

In which part of the mitochondria does the Krebs cycle take place?
a. Inner mitochondrial membrane
b. Outer mitochondrial membrane
c. Cristae
d. Mitochondrial matrix
e. Inner-membrane space

Answer 1

Mitochondria is popularly known as the “Powerhouse of the cell,” mitochondria. It has a double membrane-bound organelle. It is found in most eukaryotic organisms. They are found inside the cytoplasm and special functions as the cell’s digestive system. They play an important role in breaking down nutrients and creating energy-rich molecules for the cell. Many of the biochemical reactions that take place in cellular respiration take place within the mitochondria.

Complete answer:
The Krebs cycle is also the Citric acid cycle. It is a series of enzyme-catalyzed reactions that occur in the mitochondrial matrix. Here $\text{acetyl} - CoA$ is oxidized to make carbon dioxide and coenzymes are reduced, which generates $ATP$ molecules in the electron transport chain.

It is an eight-step process, where the acetyl group of $acetyl - CoA$ is oxidized to form two molecules of $C{O_2}$ and in the process, one ATP is produced. Minimized high energy compounds, $NADH$ , and $FAD{H_2}$ are also produced.

Two molecules of $acetyl - CoA$ are formed from each of the glucose molecules so two turns of the Krebs cycle are required which yields four $C{O_2}$ , six $NADH$ , two $FAD{H_2}$ , and two ATPs.

Cellular respiration is a catabolic reaction that takes place in the cells. It is a biochemical process, where nutrients are broken down to release energy, which gets stored in the form of $ATP$ , and waste products are released. In aerobic respiration, oxygen is required.

Hence, the correct answer is option (D).

Additional information:
Products of Krebs cycle are listed below:
• $2$ molecules of $C{O_2}$ are released. Removal of $C{O_2}$ or decarboxylation of citric acid takes place at two places.
• In the change of isocitrate $\left( {6C} \right)$ to $\alpha$ - ketoglutarate $\left( {5C} \right)$ .
• In the change of $\alpha$ - ketoglutarate $\left( {5C} \right)$ to succinyl CoA $\left( {4C} \right)$ .
• $1\text{ATP}$ is formed in the conversion of succinyl CoA to succinate.

$3{{ }}NA{D^ + }$ are minimized to $NADH$ and $1{{ }}FA{D^ + }$ is converted to $FAD{H_2}$ in the below reactions:
• $\text{Isocitrate} \to \alpha - \text{ketoglutarate} \to \text{NADH}$
• $\alpha - \text{ketoglutarate} \to \text{succinyl} CoA \to \text{NADH}$
• $\text{Succinate} \to \text{fumarate} \to FAD{H_2}$
• $\text{Malate} \to \text{Oxaloacetate} \to \text{NADH}$

Note: This Krebs cycle is an enzyme-catalyzed reaction and it takes place in the mitochondrial matrix. In this process, $2$ molecules of $C{O_2}$ are released. Removal of $C{O_2}$ or decarboxylation of citric acid takes place at two places.