Question

The correct sequence of electron acceptor in ATP synthesis is (a) Cyt a \(\mathrm{a}_{3} \mathrm{~b} \mathrm{c}\) (b) Cyt b c a a \(_{3}\) (c) Cyt b c a \(_{3}\) a (d) Cyt c b a a \(_{3}\)

Short answer

The correct sequence of electron acceptor in ATP synthesis is (c) Cyt b c a a \(_{3}\).

Step-by-step solution

Understanding the ATP synthesis

ATP synthesis or oxidative phosphorylation, a process that takes place in mitochondria, involves an electron transport chain. This chain is a series of complexes that transfer electrons from electron donors to electron acceptors via redox reactions, and couples this electron transfer with the transfer of protons (H+ ions) across a membrane.

Identify stages in electron transport chain

The movement of electrons through the ETC components are in the exact sequence as: NADH/Q reductase complex (Complex I) \(\rightarrow\) Ubiquinone (Coenzyme Q or CoQ) \(\rightarrow\) Cytochrome b-c1 complex (Complex III) \(\rightarrow\) Cytochrome c \(\rightarrow\) Cytochrome c oxidase complex (Complex IV)

Matching the correct sequence

The correct sequence of electron acceptor in ATP synthesis should fit the sequence in the electron transport chain. Hence option (c) 'Cyt b c a \(_{3}\) a' matches correctly.

Key concepts

ATP Synthesis

ATP synthesis is a process that fuels the energy currency of the cell — adenosine triphosphate (ATP). This vital process occurs in the mitochondria, the powerhouse of the cell. During ATP synthesis, the electron transport chain (ETC) plays a crucial role. This chain is a series of protein complexes and other molecules that transfer electrons to help convert energy into usable ATP.

To generate ATP, electrons are transferred through a sequence of agents in the ETC. Energy used during this transfer process links the process of electron transport to the synthesis of ATP from ADP and inorganic phosphate. Essentially, it transforms energy derived from nutrients into chemical energy stored as ATP. This is fundamental to sustaining cellular functions.

Oxidative Phosphorylation

Oxidative phosphorylation is a key part of the process where ATP is made. It's the last stage of aerobic respiration, following glycolysis and the Krebs cycle. During oxidative phosphorylation, the electrons that have been released are used to power ATP synthesis via the electron transport chain.

This process occurs on the inner mitochondrial membrane and involves two main stages:

• Electron Transport Chain: Electron carriers pass electrons through multiple complexes, releasing energy used to move protons across the membrane.
• ATP Synthase Action: Protons flow back through the enzyme ATP synthase, driving the production of ATP.

Oxidative phosphorylation is very efficient, enabling the majority of the cell's ATP production.

Mitochondria

Mitochondria are often called the powerhouses of cells due to their role in energy production. This organelle is where the magic of ATP synthesis happens, specifically on the inner membrane where the electron transport chain is located.

Key features of mitochondria include:

• Double Membrane Structure: They have an inner and outer membrane. The inner membrane folds extensively to form cristae, increasing surface area for ATP production.
• Matrix: The space inside the inner membrane contains DNA, ribosomes, and enzymes necessary for ATP production and other chemical reactions.
• Electron Transport Chain Location: Embedded within the inner membrane, the ETC facilitates oxidative phosphorylation.

Mitochondria are crucial for supplying the cell with energy rich in ATP.

Cytochrome Complexes

Cytochrome complexes are vital in the electron transport chain. They help transfer electrons and facilitate ATP production. These complexes are part of the series that includes distinct members, each playing a specific role in the chain.

The main cytochrome complexes include:

• Cytochrome b-c1 Complex (Complex III): Receives electrons from ubiquinone, helps move protons across the membrane.
• Cytochrome c: A small protein that transfers electrons between Complex III and Complex IV.
• Cytochrome c Oxidase Complex (Complex IV): Transfers electrons to oxygen, the final electron acceptor, facilitating the production of water and contributing to proton gradient for ATP synthesis.

Each cytochrome complex is integral to electron transport, ensuring that energy transfer is efficient for ATP production.