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

Cytochrome c is needed for efficient electron transfer in oxidative phosphorylation, and its source does not matter due to its conserved structure and function across species.

Step-by-step solution

Introduction to Cytochrome c

Understand that cytochrome c is a small heme protein that is a component of the electron transport chain in mitochondria. It plays a crucial role in the process of oxidative phosphorylation, transferring electrons between Complex III and Complex IV.

Role in Oxidative Phosphorylation

Recognize that in oxidative phosphorylation, cytochrome c transfers electrons from cytochrome bc1 (Complex III) to cytochrome c oxidase (Complex IV). This electron transfer is essential for the production of ATP.

Reason for Adding Purified Cytochrome c

The experiment specifies the addition of purified cytochrome c to ensure that there is a sufficient amount of this protein for efficient electron transfer between Complex III and IV. This helps to optimize the reactions and ensures accurate experimental results.

Source of Cytochrome c

The source of cytochrome c does not need to be the same as the mitochondria because cytochrome c from various sources, such as different species, is highly conserved in its structure and function. This means cytochrome c from another source can effectively replace the native cytochrome c in the reaction system.

Key concepts

cytochrome c

Cytochrome c is a small, but essential, protein found in the mitochondria's electron transport chain. It is part of a group of proteins known as cytochromes, which contain a heme group responsible for their ability to transfer electrons. Cytochrome c specifically is crucial for oxidative phosphorylation, the process through which the cell produces ATP, the main energy currency of biological systems.
During oxidative phosphorylation, cytochrome c transfers electrons from Complex III (cytochrome bc1) to Complex IV (cytochrome c oxidase). This electron transfer is essential as it helps drive the synthesis of ATP, ensuring the cell has enough energy for various tasks.
The function and structure of cytochrome c are highly conserved across different species. This is why adding purified cytochrome c from any source to an experimental set-up with mitochondria works effectively. It means the role of cytochrome c in electron transfer can be carried out even if the protein doesn't originate from the same species as the mitochondria used in the experiment.

electron transport chain

The electron transport chain (ETC) is a series of protein complexes located in the inner mitochondrial membrane. It plays a critical role in the production of ATP through a process called chemiosmosis. The ETC is composed of four main complexes: Complex I, Complex II, Complex III, and Complex IV.
Electrons derived from nutrients travel through these complexes. Here’s a simplified breakdown:

• Electrons enter the ETC through Complex I from NADH or through Complex II from FADH2.
• Electrons then move to Complex III.
• Cytochrome c transfers electrons from Complex III to Complex IV.
• Finally, electrons reach Complex IV, where they help in the reduction of oxygen to water.

The transfer of electrons through these complexes drives the pumping of protons from the mitochondrial matrix into the intermembrane space. This creates a proton gradient. The flow back of protons into the matrix through ATP synthase results in the production of ATP.
The efficient functioning of the ETC is crucial for energy production in cells. Any disruption in this process can lead to decreased ATP levels, impacting cellular activity and overall organism health.

mitochondria

Mitochondria are often referred to as the powerhouse of the cell. These organelles are double-membrane structures found in most eukaryotic cells. Their primary function is to generate ATP through the process of oxidative phosphorylation.
The inner membrane of the mitochondria contains the electron transport chain and ATP synthase, which are key components in ATP production. The space inside the inner membrane is known as the mitochondrial matrix, and it houses enzymes involved in the citric acid cycle (Krebs cycle), another crucial step in energy metabolism.
Mitochondria also have their own DNA, which is separate from the cell's nuclear DNA. This mitochondrial DNA encodes some of the proteins needed for the electron transport chain and other mitochondrial functions. The unique structure and function of mitochondria highlight their essential role in cellular respiration and energy production.
Additionally, mitochondria are involved in other important cellular processes, including the regulation of the cell cycle, cell growth, and apoptosis (programmed cell death). Maintaining healthy mitochondria is vital for the overall function and health of the cell.