Question

Describe the structure and function of the six electron carriers in the mitochondrial electron transport system.

Short answer

Question: Describe the structure and function of the six primary electron carriers in the mitochondrial electron transport system. Answer: In the mitochondrial electron transport system, the six primary electron carriers include: 1. NADH and FADH2, which act as primary electron donors and are derived from B-vitamins. 2. Coenzyme Q (CoQ or ubiquinone), a lipid-soluble molecule that functions as a mobile electron carrier by transferring electrons from Complex I and II to Complex III. 3. Cytochromes (b, c, c1, a, a3), which are heme-containing proteins responsible for electron transfer, and in particular, cytochrome c transfers electrons between Complex III and Complex IV. 4. Iron-sulfur proteins, such as ferredoxin, which contain iron and sulfur atoms bound to a protein and facilitate electron transfer within various ETC complexes. 5. Copper ions (Cu), found in Complex IV and organized in redox-active metal centers called CuA and CuB, which help transfer electrons from cytochrome c to molecular oxygen to produce water. Each of these electron carriers play a unique role in driving ATP synthesis through oxidative phosphorylation in the electron transport chain.

Step-by-step solution

Introduction to the Electron Transport Chain

The electron transport system, also known as the electron transport chain (ETC), is a series of protein complexes in the inner mitochondrial membrane that transfer electrons from electron donors to electron acceptors. This electron transfer process drives the synthesis of ATP through oxidative phosphorylation.

Overview of the Six Electron Carriers

There are six primary electron carriers in the mitochondrial electron transport system: NADH, FADH2, Coenzyme Q (CoQ or ubiquinone), Cytochromes (b, c, c1, a, and a3), Iron-sulfur proteins and Copper ions (Cu). Each of these electron carriers has a unique structure and function in the ETC.

NADH and FADH2

NADH and FADH2 are the primary electron donors in the mitochondrial electron transport system. They are derived from the oxidation of metabolic substrates and provide high-energy electrons to the ETC. NADH is a coenzyme derived from the B-vitamin niacin, while FADH2 is derived from the B-vitamin riboflavin. They both transfer their electrons to the first protein complex (Complex I or III, respectively) to initiate the electron transport process.

Coenzyme Q (CoQ or Ubiquinone)

Coenzyme Q (CoQ or ubiquinone) is a small, lipid-soluble molecule that functions as a mobile electron carrier in the ETC. CoQ can accept electrons from Complex I and Complex II and transfer them to Complex III. The hydrophobic nature of CoQ allows it to move freely within the inner mitochondrial membrane, making it an efficient electron shuttle between these complexes.

Cytochromes

Cytochromes are a family of heme-containing proteins that function as electron carriers in the mitochondrial ETC. They have different types such as b, c, c1, a, and a3, each with their specific roles in the electron transport system. The heme group binds to the protein and allows them to facilitate the transfer of electrons. Cytochrome c, in particular, acts as a mobile electron carrier transferring electrons between Complex III and Complex IV.

Iron-Sulfur Proteins

Iron-sulfur proteins are another family of electron carriers present in several protein complexes of the ETC. They consist of iron and sulfur atoms bound to the protein, which facilitate electron transfer. One of the most well-known iron-sulfur proteins is ferredoxin, found in Complex I, II, and III. These proteins have varying numbers of iron-sulfur clusters, and they help to transfer electrons within the ETC complexes.

Copper Ions (Cu)

Copper ions (Cu) function as electron carriers in Complex IV (cytochrome c oxidase) of the mitochondrial ETC. They're organized in redox-active metal centers called CuA and CuB, which allows them to accept and donate electrons. Copper ions play a crucial role in the transfer of electrons from cytochrome c to the final electron acceptor, molecular oxygen, to produce water. By understanding the structure and function of these six electron carriers, we can better appreciate the complex mechanisms occurring in the mitochondrial electron transport system and how they drive ATP synthesis via oxidative phosphorylation.