Oxidative Phosphorylation | Respiration | Revision for Biology A-Level and IB

Summary

This video explains oxidative phosphorylation, the final stage of cellular respiration, where most of the cell’s ATP is produced. It covers key concepts such as ATP structure, the electron transport chain, and the role of oxygen as the final electron acceptor. The process involves electron transfer through protein complexes, proton pumping, and ATP synthesis via ATP synthase. The video also discusses the impact of inhibitors like cyanide, which block ATP production, and explores the theoretical and actual ATP yields from respiration, with oxygen being crucial for the process to function properly.

Takeaways

• 😀 ATP (adenosine triphosphate) is the energy currency of the cell, consisting of a nitrogenous base (adenine), a ribose sugar, and three phosphate groups.
• 😀 ATP is produced during respiration and photosynthesis, and it is used to power energy-requiring processes like active transport and molecule synthesis.
• 😀 Oxidative phosphorylation is the final stage of cellular respiration, where most ATP is generated, occurring in the folds of the inner mitochondrial membrane.
• 😀 The electron transport chain (ETC) involves a series of redox reactions where electrons are transferred from NADH and FADH2 to electron carrier proteins in the inner mitochondrial membrane.
• 😀 As electrons move through the ETC, energy is released, which is used to actively pump hydrogen ions (H+) into the intermembrane space, creating a concentration gradient.
• 😀 Hydrogen ions can only diffuse back into the mitochondrial matrix through ATP synthase, and this flow drives the synthesis of ATP.
• 😀 NADH produces more ATP than FADH2 because it donates electrons earlier in the electron transport chain, resulting in more energy being released.
• 😀 Oxygen acts as the final electron acceptor in the electron transport chain. Without oxygen, the chain would cease, halting ATP production and leading to cell death.
• 😀 Cyanide is a respiratory inhibitor that blocks the cytochrome oxidase enzyme, preventing oxygen from accepting electrons and stopping ATP production.
• 😀 The theoretical yield of ATP from one molecule of glucose is 38, but due to inefficiencies like energy used for molecule transport, the actual yield is around 32 ATP.
• 😀 ATP production involves multiple stages: glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation, with oxygen being essential for the final step of ATP synthesis.

Q & A

What is ATP, and why is it referred to as the 'energy currency' of the cell?

ATP (Adenosine Triphosphate) is a molecule composed of a nitrogenous base (adenine), a ribose sugar, and three phosphate groups. It is referred to as the 'energy currency' because it stores and releases energy for cellular processes, similar to how money is exchanged for goods and services. ATP is produced in respiration and photosynthesis and can be broken down to release energy for processes like active transport and molecule building.

What is oxidative phosphorylation, and how is it related to ATP production?

Oxidative phosphorylation is the final stage of cellular respiration, where the majority of ATP is produced. This process occurs in the inner mitochondrial membrane, where a proton gradient is created through the electron transport chain. The flow of protons back through ATP synthase drives the production of ATP from ADP and inorganic phosphate.

How do NADH and FADH2 contribute to ATP production during oxidative phosphorylation?

NADH and FADH2 are coenzymes that donate electrons and protons to the electron transport chain. NADH donates electrons to the first protein complex in the chain, while FADH2 donates electrons to the second complex. The movement of electrons through the chain generates energy used to pump protons into the intermembrane space, creating a proton gradient that drives ATP synthesis.

What role does oxygen play in oxidative phosphorylation?

Oxygen acts as the final electron acceptor in the electron transport chain. At the end of the chain, oxygen combines with electrons and protons to form water. Without oxygen, electrons would not have a place to go, causing the entire electron transport chain to halt and preventing ATP production.

What happens if there is no oxygen available during cellular respiration?

If oxygen is not available, the electron transport chain cannot function, which halts the movement of electrons through the chain. As a result, no proton gradient is formed, and ATP production via oxidative phosphorylation stops. This can lead to a dramatic decrease in ATP production, causing cells to die without enough energy.

How does cyanide affect cellular respiration?

Cyanide is a respiratory inhibitor that affects the electron transport chain. It inhibits the cytochrome oxidase enzyme, which is responsible for transferring electrons to oxygen. Without this enzyme activity, oxygen cannot accept electrons, which disrupts the electron flow and halts ATP production, making cyanide a potent poison.

How is the ATP yield from NADH and FADH2 different?

NADH produces 3 ATP molecules for each molecule that enters the electron transport chain, while FADH2 produces only 2 ATP molecules. This difference is due to the fact that NADH donates electrons to a higher energy complex in the electron transport chain, allowing more energy to be harnessed for proton pumping.

Why is the theoretical maximum ATP yield from glucose not always achieved?

The theoretical maximum ATP yield from glucose is not always achieved because some energy is used in processes like transporting ADP into the mitochondria, transporting pyruvate into the matrix, and moving ATP out of the mitochondria. These processes reduce the overall efficiency of ATP production, leading to a lower actual ATP yield.

How many ATP molecules are theoretically produced from one molecule of glucose during respiration?

Theoretically, one molecule of glucose can produce up to 38 ATP molecules during cellular respiration. This includes contributions from NADH, FADH2, and ATP produced directly in glycolysis and the Krebs cycle.

What are the differences between NADH and FADH2 in terms of ATP production?

NADH is more efficient in ATP production than FADH2. Each NADH molecule can produce 3 ATP molecules, while each FADH2 molecule produces 2 ATP molecules. This is because NADH enters the electron transport chain at a higher energy level, releasing more energy as it moves through the chain.