Question

Which type of phosphorylation occurs in mitochondria? (a) Oxidative phosphorylation (b) Substrate level phosphorylation (c) Photophosphorylation (d) Both (a) and (b)

Short answer

The correct answer is (d) Both (a) and (b).

Step-by-step solution

Understand Types of Phosphorylation

Oxidative phosphorylation is the metabolic pathway that uses energy released by the oxidation of nutrients to produce ATP. It occurs in the mitochondria. Substrate level phosphorylation is the metabolic reaction that results in the formation of ATP or GTP by the direct transfer of a phosphoryl (PO3) group to ADP or GDP from another phosphorylated compound. Photophosphorylation occurs in the chloroplasts of plants where light energy is used to create a high-energy electron donor and an electron acceptor.

Identify the Right Phosphorylation in Mitochondria

From the understanding in step 1, we know that Oxidative phosphorylation occurs in the mitochondria, while Photophosphorylation occurs in the chloroplasts of plants. It's also noted that Substrate level phosphorylation does takes place in mitochondria during the process of glycolysis and Krebs cycle.

Choose The Correct Answer

Given all of this information, we can conclude that both Oxidative phosphorylation and Substrate level phosphorylation occur in mitochondria. Thus the correct answer is option (d) Both (a) and (b).

Key concepts

Substrate Level Phosphorylation

Substrate level phosphorylation is one of the ways cells can produce ATP, which is the energy currency of the cell. Unlike oxidative phosphorylation, this process does not require membranes or oxygen, and it happens directly in the cytoplasm of the cell and also in the mitochondria. This process involves the direct transfer of a phosphate group to adenosine diphosphate (ADP) from another phosphorylated molecule. Some examples of where substrate level phosphorylation occurs are during glycolysis and the Krebs cycle.

• In glycolysis, glucose is broken down into pyruvate, producing a small amount of ATP through substrate level phosphorylation.
• During the Krebs cycle, a key part of cellular respiration that occurs in the mitochondrial matrix, more ATP is generated in a similar manner.

Even though substrate level phosphorylation produces less ATP compared to oxidative phosphorylation, it is crucial because it allows cells to gain energy quickly under conditions where oxygen might not be available.

Mitochondria

Mitochondria are often referred to as the powerhouses of the cell. They are double-membraned organelles found in most eukaryotic cells. Their main role is to perform cellular respiration, a process where nutrients are converted into energy that the cell can use. Inside the mitochondria, the inner membrane is folded into structures known as cristae. This increases surface area, which is advantageous for the various reactions involved in ATP synthesis.

• Oxidative phosphorylation, the most significant ATP-producing process, occurs along the inner mitochondrial membrane.
• The Krebs cycle takes place in the mitochondrial matrix, further contributing to ATP production.

Mitochondria are unique because they have their own DNA and ribosomes, suggesting an evolutionary past where they may have been independent organisms. This organelle is not only vital for energy production but also plays roles in apoptosis (programmed cell death) and the regulation of cellular metabolism.

ATP Production

ATP, or adenosine triphosphate, is often called the "energy currency" of the cell because it efficiently stores and transfers energy necessary for various cellular functions. There are two main processes through which ATP is produced:

• Oxidative Phosphorylation: This process occurs in the mitochondria and is the most prolific producer of ATP. It utilizes the electron transport chain and chemiosmosis to generate ATP from ADP, utilizing oxygen.
• Substrate Level Phosphorylation: As mentioned before, this method does not rely on the electron transport chain and occurs in the cytoplasm during glycolysis and in the mitochondria during the Krebs cycle.

In total, these processes allow a cell to produce vast amounts of ATP efficiently, ensuring that cellular reactions that require energy, such as muscle contractions, nerve impulses, and biosynthesis of molecules, can proceed seamlessly.