cell biology · BEGINNER LESSON
Mitochondrion
A mitochondrion is a membrane-bound organelle in eukaryotic cells that carries out most cellular oxidation and makes much of the cell’s adenosine triphosphate (ATP), the molecule used to store usable chemical energy. It has two membranes, and many cells contain many mitochondria because their energy demand is high.
What it is and what it measures
A mitochondrion is a structure inside eukaryotic cells. Its main observable job is energy production: it converts energy from fuels into ATP, which is the cell’s immediate energy currency. In many tissues, cells contain many mitochondria because they need more ATP. Mitochondria also occupy a substantial part of the cell interior and are often described as small, elongated bodies, although living mitochondria can constantly change shape.
[1] The Mitochondrion - Molecular Biology of the Cell - NCBI Bookshelf [2] Mitochondria
How it works
Mitochondria complete the oxidation of fuels such as pyruvate, which comes from sugars, and fatty acids, which come from fats. These fuels are converted in the mitochondrial matrix to acetyl coenzyme A (acetyl CoA), a key intermediate in metabolism. High-energy electrons removed from fuels are carried by nicotinamide adenine dinucleotide in its reduced form (NADH) and flavin adenine dinucleotide in its reduced form (FADH2). Those electrons move through the respiratory chain, an electron-transport chain in the inner mitochondrial membrane. As electrons pass along this chain, molecular oxygen is directly consumed at the end, water is formed, and the released energy is used to convert adenosine diphosphate (ADP) plus inorganic phosphate (Pi) into ATP. This process is called oxidative phosphorylation.
[1] The Mitochondrion - Molecular Biology of the Cell - NCBI Bookshelf [3] Functional Mitochondria in Health and Disease - PMC
Why mitochondria matter
Because mitochondria complete fuel oxidation and make most ATP, they support many energy-hungry cell functions. Cells with high energy use, such as muscle, tend to have many mitochondria. Mitochondria also form networks that can expand by fusion or be reduced by fission and mitophagy, which is the removal of mitochondria. This flexibility helps cells adjust to changing energy needs.
[2] Mitochondria [3] Functional Mitochondria in Health and Disease - PMC
Limitations and important caveats
Mitochondria do not use oxygen for every step of their metabolism. The citric acid cycle is considered part of aerobic metabolism, but direct oxygen use happens in the final reactions on the inner mitochondrial membrane. Mitochondria are also not fixed shapes: they can fuse, split, and move. Finally, their function depends on communication with the nucleus; if mitochondrial DNA or respiratory-chain proteins are damaged, oxidative phosphorylation can fail and the cell’s energy supply can drop.
[1] The Mitochondrion - Molecular Biology of the Cell - NCBI Bookshelf [3] Functional Mitochondria in Health and Disease - PMC
SEE THE IDEA
How a mitochondrion makes ATP
Pyruvate from sugars or fatty acids from fats enter the mitochondrion.
Fuel is converted to acetyl CoA in the mitochondrial matrix.
NADH and FADH2 pass electrons through the respiratory chain.
Energy drives ADP + Pi to ATP while oxygen is reduced to water.
Fuel is broken down step by step, and the released energy is captured as ATP.
A mitochondrion converts fuel energy into ATP through matrix reactions and an inner-membrane electron-transport chain.
TRY IT YOURSELF
Test your understanding
Choose an answer, then check the explanation.
PUT IT TOGETHER
Match each concept to its meaning
Drag a label onto its description, or select a label and then select a description. This also works with a keyboard.
4 pairs to match
Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.