Question

Two biochemistry students are about to use mitochondria isolated from rat liver for an experiment on oxidative phosphorylation. The directions for the experiment specify addition of purified cytochrome \(c\) from any source to the reaction mixture. Why is the added cytochrome \(c\) needed? Why does the source not have to be the same as that of the mitochondria?

Short answer

The added cytochrome c ensures sufficient electron carriers for the ETC. Its source does not matter because of the protein’s conserved structure and function.

Step-by-step solution

- Understanding Cytochrome c

Cytochrome c is a small heme protein found in the intermembrane space of mitochondria. It plays a crucial role in the electron transport chain (ETC), which is vital for oxidative phosphorylation.

- Role in Electron Transport Chain

In the ETC, cytochrome c serves as an electron carrier, transferring electrons between Complex III (cytochrome bc1 complex) and Complex IV (cytochrome c oxidase).

- Importance of Adding Purified Cytochrome c

In the isolated mitochondria experiment, adding purified cytochrome c ensures that there are sufficient amounts of this protein to facilitate continuous electron transfer between the complexes of the ETC, thereby supporting ongoing oxidative phosphorylation.

- Source of Cytochrome c

The cytochrome c used in the experiment does not need to come from the same source as the mitochondria because cytochrome c is highly conserved across different species. This means its structure and function are very similar regardless of its origin, allowing it to interact properly with the rat liver mitochondria.

Key concepts

cytochrome c

Cytochrome c is a small protein that resides in the intermembrane space of mitochondria. It has a critical function in the process of oxidative phosphorylation, occurring within the cells. Specifically, cytochrome c acts as an electron carrier. This means it transfers electrons from one molecule to another in the electron transport chain (ETC). Its role is to help facilitate this energy-producing chain, making it essential for cellular respiration. Though it's tiny, cytochrome c is highly conserved across species. This means its structure is very similar in different organisms, so cytochrome c from one source can efficiently work with mitochondria from another.

electron transport chain

The electron transport chain (ETC) is a series of protein complexes located in the inner membrane of mitochondria. It plays a central role in producing ATP, the energy currency of the cell, through oxidative phosphorylation. The ETC consists of four main complexes known as Complex I, II, III, and IV. Electrons travel through these complexes, starting from donors like NADH and FADH2 and moving to acceptors like oxygen, forming water.

As electrons move through these complexes, protons are pumped from the mitochondrial matrix into the intermembrane space. This creates a proton gradient that drives the synthesis of ATP by the enzyme ATP synthase. Cytochrome c specifically transfers electrons between Complex III (cytochrome bc1 complex) and Complex IV (cytochrome c oxidase), ensuring that this essential energy-producing process can continue smoothly.

mitochondria

Mitochondria are often called the powerhouses of the cell. These small, double-membraned organelles are key players in energy production. They perform oxidative phosphorylation, a process that generates ATP through the electron transport chain (ETC).

Mitochondria have their own DNA, distinct from the cell's nuclear DNA, and they can reproduce independently within the cell. This unique feature supports the theory that mitochondria originated from free-living bacteria that entered into a symbiotic relationship with early eukaryotic cells.

Within mitochondria, the inner membrane is highly folded into structures known as cristae, which increase the surface area for the ETC and ATP production. This optimization ensures efficient production of ATP to meet the cell's energy demands.

In the context of experiments with isolated mitochondria, such as those involving rat liver mitochondria, it is important to ensure that all necessary components like cytochrome c are present. This keeps the ETC running effectively, allowing researchers to study oxidative phosphorylation and related biochemical processes.