Mitochondrial threshold effect is a phenomenon where the number of mutated

mtDNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the DNA contained in ...

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 which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

and ATP synthesis of a

mitochondrion A mitochondrion () is an organelle found in the cell (biology), cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosine tri ...

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 Mitochondrial disease is a group of disorders caused by mitochondrial dysfunction. Mitochondria are the organelles that generate energy for the cell and are found in every cell of the human body except red blood cells. They convert the energy o ...

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 Cell (biology), cells use enzymes to Redox, oxidize nutrients, thereby releasing chemical energy in order ...

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 (physical form and structure), its developmental processes, its biochemical and physiological propert ...

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