Cellular Respiration

Index to this page


C6H12O6 + 6O2 + 6H2O 12H2O + 6 CO2





Mitochondria have:


The number of mitochondria in a cell can


The Outer Membrane


The Inner Membrane

The inner membrane contains 5 complexes of integral membrane proteins:

The Matrix


Here pyruvic acid is

The Citric Acid Cycle

The citric acid cycle is also known as the Krebs cycle (after the biochemist who worked it out) and the tricarboxylic acid cycle (TCA). The steps:



The Electron Transport Chain


The electron transport chain accomplishes:

Chemiosmosis in mitochondria




External Link
Scroll down the left-hand column at this link to view animations of ATP synthase, the electron transport chain and others on "cellular energy conversion".

How many ATPs?



With 12 pairs of electrons removed from each glucose molecule,

this could generate 34 ATPs.




The three exceptions

A stoichiometric production of ATP does occur at:

Mitochondrial DNA (mtDNA)


The rRNA and tRNA molecules are used in the machinery that synthesizes the 13 proteins.

The 13 proteins participate in building several protein complexes embedded in the inner mitochondrial membrane.


Mutations in mtDNA cause human diseases.

Mutations in 12 of the 13 protein-encoding mitochondrial genes have been found to cause human disease.


Some of these disorders are inherited in the germline. In the vast majority of cases, the mutant gene is received from the mother because only very rarely do the mitochondria in sperm survive in the fertilized egg.

Other disorders are somatic; that is, the mutation occurs in the somatic tissues of the individual. These disorders can be caused not only by mutations in mtDNA, but also by mutations in the 228 nuclear genes that have also been implicated in human mitochondrial diseases. These latter mutations can be inherited from the father as well as the mother.

Example: exercise intolerance



Mitochondrial Replacement Techniques

As I noted above, only mothers can pass mutant mtDNA on to their offspring. Two techniques are under intense investigation, either of which could enable a mother to have children free of defective mitochondria. These techniques (numbers 1 and 2) are described on another page [Link to it].

Mutations in some 228 nuclear genes have also been implicated in human mitochondrial diseases, but mitochondrial replacement techniques will not be able to help with these.

Why do mitochondria have their own genome?


The recent sequencing of the complete genome of the endosymbiotic alpha-proteobacterium Rickettsia prowazekii has revealed a number of genes closely related to those found in mitochondria. This suggests a shared ancestry.

Further discussion of the evolutionary implications of mtDNA.
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17 May 2019