Mitochondrial threshold effect is a phenomenon where the number of mutated

mtDNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondrion, mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mit ...

has surpassed a certain threshold which causes the

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couple ...

and ATP synthesis of a

mitochondrion A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is use ...

to fail. There isn't a set number that needs to be surpassed, however, it is associated with an increase of the number of mutated

. When there is 60-80% of mutated

present, that is said to be the threshold level. While 60-80% is the general threshold level, this is also dependent on the individual, the specific organ in question and what the specific mutation is. There are three specific types of mitochondrial threshold effects: phenotypic threshold effect, biochemical threshold effect and translational threshold effect. Threshold expression is a phenomenon in which phenotypic expression of a mitochondrial disease within an organ system occurs when the severity of the mutation, relative number of mutant

, and reliance of the organ system on

oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine t ...

combine in such a way that ATP production of the tissue falls below the level required by the tissue. The

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological prop ...

may be expressed even if the percentage of mutant mtDNA is below 50% if the mutation is severe enough.

Phenotypic threshold effect

Phenotypic threshold effect is when there is a certain amount of wild-type

present in the

which is able to balance out the number of mutated

. As a result, the

is normal. However, if the number of wild-type

decreases and the number of mutant

increases, resulting in an imbalance between the two, the threshold level has been altered which causes complications. This occurs because the wild-type

present are able to keep the

and ATP synthesis functioning despite there being a few number of them present. They are able to counterbalance the mutated

, however, when the number drops below threshold level the mutant

take over.

Phenotypic threshold effect

See also

References

Further reading