Mitochondria

Learning Goals

By the end of this lesson, you will be able to:

• Explain the basic substructures of mitochondria
• Describe the basic function of mitochondria in cells

Key Vocabulary:

• Mitochondria: a type of organelle also known as the “powerhouse of the cell” because it creates the energy (ATP) used by the cell to carry out its functions.

• Semi-autonomous: an organelle that can replicate and express its own DNA

• Chemiosmosis: ​​a process that occurs in the mitochondria of cells where the movement of ions across a selectively permeable membrane creates a gradient that is used to generate ATP (adenosine triphosphate)

Mitochondria’s Structure

Mitochondria are like tiny power plants inside our cells. They have a double layer of membrane, where the outer layer is smooth and made of lipids, while the inner layer is folded into little finger-like structures called cristae. These cristae give the inner membrane a lot of surface area for energy production. Special enzymes in the inner membrane use this surface area to make a molecule called ATP, which is like a battery for our cells.

The space between the two layers of the membrane is called the intermembrane space, while the space inside the inner membrane is called the matrix. It is in the intermembrane space that a process called chemiosmosis happens. Chemiosmosis is the process where the energy made during cellular respiration is used to move hydrogen ions across the inner membrane of the mitochondria, creating a proton gradient.

This proton gradient is used by another special enzyme called ATP synthase to make ATP. ATP gives our cells the energy they need to function properly.

Check out the video below for a quick animation of the process of chemiosmosis.

What does it mean when we say that Mitochondria are semi-autonomous?

Mitochondria have their own genetic material, separate from the cell’s nuclear DNA. This genetic material is found in the form of a small circular DNA molecule, called the mitochondrial DNA (mtDNA). This means that mitochondria can replicate and express their own genes, making them semi-autonomous. Mitochondria also all have their own ribosomes and can make their own proteins. They’re almost like a cell within a cell!

Note: The proteins synthesized by the mitochondria are mostly involved in the production of energy. For example, the enzymes of the electron transport chain, which are responsible for the production of ATP, are all synthesized by the mitochondrial ribosomes. 

Apoptosis

Mitochondria play a key role in cell death, also known as apoptosis. Apoptosis is a programmed process that occurs in cells in response to certain signals, such as DNA damage or viral infection. When a cell receives these signals, the mitochondria release a group of proteins called cytochrome c, which triggers a cascade of events that lead to the death of the cell.

NurseHub Note: Did you know that we have webbing between our toes and fingers when we’re in the womb? The reason that webbing has disappeared by the time we’re born is because of apoptosis. A signal is sent to the cells that make up that webbing to die, which is why the webbing goes away.

So, what should you remember about Mitochondria? 

• Mitochondria are the powerhouses of the cell and produce ATP, which the cell uses for energy.
• Mitochondria have a double membrane structure.
• Mitochondria are semi-autonomous due to the presence of their own genetic material and ribosomes.
• Mitochondria participate in programmed cell death.
• Mitochondria are responsible for protein synthesis, specifically for energy production.

Quick Quiz Time!