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An introduction to the mitochondria and its inner and outer membrane

By Editors Mitochondria Definition Mitochondria singular: Mitochondria are found in all eukaryotes, which are all living things that are not bacteria or archaea. It is thought that mitochondria arose from once free-living bacteria that were incorporated into cells.

  • The folding of the inner membrane increases the surface area inside the organelle;
  • Thus, although the targeting signals for signal-anchored proteins appear to be conserved in all eukaryotes, this is not the case for the factors mediating their biogenesis;
  • However, as in yeast but unlike in plants and humans, these residues are not essential for mitochondrial targeting but do influence the strength of the interaction with the OM.

Function of Mitochondria Mitochondria produce ATP through process of cellular respiration —specifically, aerobic respirationwhich requires oxygen. The citric acid cycle, or Krebs cycle, takes place in the mitochondria.


This cycle involves the oxidation of pyruvate, which comes from glucose, to form the molecule acetyl-CoA. NADH is then used in the process of oxidative phosphorylationwhich also takes place in the mitochondria. Electrons from NADH travel through protein complexes that are embedded in the inner membrane of the mitochondria. This set of proteins is called an electron transport chain.

Structure of Mitochondria

Energy from the electron transport chain is then used to transport proteins back across the membrane, which power ATP synthase to form ATP. The amount of mitochondria in a cell depends on how much energy that cell needs to produce. Muscle cells, for example, have many mitochondria because they need to produce energy to move the body.

Red blood cells, which carry oxygen to other cells, have none; they do not need to produce energy.

Organization and Function of Mitochondria

Mitochondria are analogous to a furnace or a powerhouse in the cell because, like furnaces and powerhouses, mitochondria produce energy from basic components in this case, molecules that have been broken down so that they can be used. Mitochondria have many other functions as well.

They can store calcium, which maintains homeostasis of calcium levels in the cell. Structure of Mitochondria Mitochondria have two membranes, an outer membrane and an inner membrane. The outer membrane covers the surface of the mitochondrion, while the inner membrane is located within and has many folds called cristae. The folds increase surface area of the membrane, which is important because the inner membrane holds the proteins involved in the electron transport chain.

The space between the outer and inner membranes is called the intermembrane space, and the space inside the inner membrane is called the matrix. This diagram shows the structure of a mitochondrion. Evolution of Mitochondria Mitochondria are thought to have evolved from free-living bacteria that developed into a symbiotic relationship with a prokaryotic cell, providing it energy in return for a safe place to live.

It eventually became an organelle, a specialized structure within the cell, the presence of which are used to distinguish eukaryotic cells from prokaryotic cells. This occurred over a long process of millions of years, and now the mitochondria inside the cell cannot live separately from it.

The idea that mitochondria evolved this way is called endosymbiotic theory. Endosymbiotic theory has multiple forms of evidence. It is called mitochondrial DNA or mtDNA, and it is only passed down through females because sperm do not have mitochondria.

  1. Some cells have several thousand mitochondria while others have none. The Genetic System of Mitochondria Mitochondria contain their own genetic system, which is separate and distinct from the nuclear genome of the cell.
  2. Since these interactions of polypeptide chains with molecular chaperones depend on ATP, protein import requires ATP both outside and inside the mitochondria, in addition to the electric potential across the inner membrane.
  3. Because of the double-membrane structure of mitochondria, the import of proteins is considerably more complicated than the transfer of a polypeptide across a single phospholipid bilayer.
  4. Mitochondria are analogous to a furnace or a powerhouse in the cell because, like furnaces and powerhouses, mitochondria produce energy from basic components in this case, molecules that have been broken down so that they can be used.

You received your mtDNA from your mother, and you can only pass it on if you are a female who has a child. It is also circular, like bacterial DNA. Another form of evidence is the way new mitochondria are created in the cell.


New mitochondria only arise from binary fission, or splitting, which is the same way that bacteria asexually reproduce. Also, the genome of mitochondria and Rickettsia bacteria bacteria that can cause spotted fever and typhus have been compared, and the sequence is so similar that it suggests that mitochondria are closely related to Rickettsia.

Chloroplasts, the organelles in plants where photosynthesis occurs, are also thought to have evolved from endosymbiotic bacteria for similar reasons: Related Biology Terms Adenosine triphosphate — The main energy molecule used to power cellular activities; it is produced by mitochondria.

Mitochondria - Turning on the Powerhouse

Endosymbiotic theory — The idea that mitochondria and chloroplasts in plants evolved from bacteria that was once free-living being incorporated into the cell. Electron transport chain — A step in oxidative phosphorylation and the production of ATP where electrons travel through a series of protein complexes.

Citric acid cycle — A series of chemical reactions in the matrix of the mitochondria that releases energy through the oxidation of acetyl-CoA. Which is a function of mitochondria?