Mitochondria-Definition, Structure, Functions And Diagram

Mitochondria Definition

  • The oxygen-consuming, very significant mitochondria are floating free inside every cell and are formed like ribbons.
  • They are referred to as the “powerhouse of the cell” since they oxidise the available substrates to provide the organism with all the biological energy it needs.
  • Energy is produced in the mitochondria during the enzymatic oxidation of chemical molecules.
  • Since they serve as the energy centres, mitochondria may be present in abundance on the sperm tail, muscle cells, liver cells (which can have up to 1600 mitochondria), microvilli, as well as oocytes (which can contain more than 300,000 mitochondria) and other locations.
  • Typically, a cell has around 2000 mitochondria, which account for approximately 25% of the cell’s mass.
  • Richard Altmann originally identified mitochondria in 1890 and referred to them as “bioblasts.” Benda first used the word “mitochondrion” in 1897.

Structure of Mitochondria

Double-membrane organelles with moveable and flexible membranes are mitochondria. Its diameter varies from 0.5 to 1.0 micrometres. The matrix, the intermembrane space, the outer membrane, and two membranes surround the organelle: a thin outside membrane.

  • The organelle is surrounded by two membranes: a smooth outer membrane and an inner mitochondrial membrane that is noticeably folded or tubular, has a significant surface area, and encloses the matrix space.
  • The intermembrane gap is located between both the inner and outer membranes.
  • From one kind of cell to another, the quantity, size, and number of cristae present in the mitochondria may vary significantly.
  • Heart muscle is one example of a tissue with an active oxidative metabolism that has cristae in abundance in mitochondria.
  • The form of the mitochondria might change even within a single kind of tissue, depending on how well they are functioning.
  • Proteins are present in abundance in both mitochondrial membranes.

Outer Mitochondrial Membrane

  • The outer mitochondrial membrane is much like the plasma membrane in terms of structure and chemical composition.
  • Porins in the outer membrane allow small molecules to travel back and forth within the cytoplasm and also the intermembrane space.

Inner Mitochondrial Membrane

  • There are a lot of different enzymes, coenzymes, and other elements of the electron transport chain in the inner mitochondrial membrane. Additionally, it has multiple permease proteins and proton pumps for the transportation of different compounds such as citrates, ADP, phosphate, and ATP.
  • The inner mitochondrial membrane emits finger-like protrusions (cristae) in the direction of the mitochondrion’s lumen and includes tennis-racket-shaped F1 particles that are responsible for ATP production thanks to the ATP-ase enzyme.
  • Even for tiny compounds, the inner mitochondrial membrane is entirely impermeable (with the exception of O2, CO2, and H2O).
  • The inner membrane contains several transporters that ensure the import and outflow of significant metabolites.

Intermembrane Space

  • Its makeup is identical to that of the cytoplasm of the cell and is the area between the mitochondria’s outer and inner membranes.
  • The intermembrane gap has a different protein composition.

Mitochondrial Matrix

  • The mitochondrial matrix, which is the liquid (colloidal) section of fully oxidised acetyl-CoA to create CO2, H2O, and hydrogen ions, is where the soluble Krebs cycle enzymes are present.
  • Hydrogen ions decrease NAD and FAD molecules, which both then send hydrogen ions to the respiratory or electron transport chain, where oxidative phosphorylation takes place to create energy-dense ATP molecules.
  • In addition, the matrix of mitochondria contains single or double-circular, double-stranded DNA molecules known as mitoribosomes and 55S ribosomes. Since mitochondria can produce 10% of their own proteins using their own machinery, they are thought of as semi-autonomous organelles.

Functions of Mitochondria

  1. The main function of mitochondria is energy generation.Mitochondria are responsible for producing adenosine triphosphate (ATP), one of the energy units used by cells to fuel a number of processes and operations.
  2. The mitochondria take in the smaller food molecules and break them down into charged molecules. ATP molecules are produced when oxygen and these charged molecules combine. This process is known as oxidative phosphorylation.
  3. Additionally, mitochondria may generate heat (brown fat), store iron-containing pigments (heme ferritin), and create the ions Ca2+ and HPO42-(or phosphate).Such as bone osteoblasts or yolk proteins).
  4. The appropriate concentration of calcium ions inside each compartment of the cell is maintained by the mitochondria.
  5. Additionally, the mitochondria play a role in the synthesis of oestrogen and testosterone, as well as several blood components.
  6. The mitochondria of the liver cell contain enzymes that detoxify ammonia.
  7. Apoptosis, or “planned cell death,” is another activity that the mitochondria are crucial to.
  8. Organ function may be impacted by abnormal cell death brought on by mitochondrial malfunction.


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  • Verma, P. S., & Agrawal, V. K. (2006). Cell Biology, Genetics, Molecular Biology, Evolution & Ecology (1 ed.). S .Chand and company Ltd.
  • https://alevelbiology.co.uk/notes/mitochondria-structure-and-functions/
  • https://biology.tutorvista.com/animal-and-plant-cells/mitochondria.html
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