Mitochondria

electron micrograph of mitochondria

Mitochondria are extremely small (from .002—.008 millimeters in length) rice-shaped structures whose details can only be seen with the electron microscope. The mitochondria shown in the figure to the left are from a mitochondria dense region of a visual cell.  A single mitochondrion in the lower right is outlined in yellow.  Mitochondria are often called the “powerhouses” of the cell because they are the site where sugar is broken down to release the energy required for cellular functions. 

A cell may have hundreds or even thousands of mitochondria depending on the particular cell’s need for energy. (For example, the average human liver cell contains more than a thousand mitochondria.) 

In addition to containing the many proteins needed to control the energy release process, the mitochondria also contain a small amount of circular DNA that is used to direct the manufacture of thirteen of the proteins needed for its activities. Mutations in the protein coding part of mitochondrial DNA can cause some human diseases, typically involving either neuromuscular dysfunction or some forms of diabetes. 

Recent evidence shows that mitochondria are also involved in other crucial functions such as cell signaling, cellular differentiation and cell death.

All Mitochondria Are Maternally Inherited
descendants chart showing the path of mitochondria inheritance
Stacks Image 10
Males sharing matrilineal line mitochondrial DNA
Stacks Image 19
Females sharing matrilineal line mitochondrial DNA
Stacks Image 13
Males NOT sharing matrilineal mitochondrial DNA
Stacks Image 27
Females NOT sharing matrilineal line mitochondrial DNA

All of an individual’s mitochondria are derived from his/her mother.  Although the sperm cell tail is packed with mitochondria to power its long journey to the egg cell, the tail and mitochondria drop off of the sperm at fertilization and do not enter the egg cell.  Sperm mitochondria that do happen to make it into the egg, are actively destroyed as soon as fertilization is complete. Consequently, all of the mitochondria in the fertilized egg come from an individual’s mother. 

[A 2002 publication by Marianne Schwartz and John Vissing from the University Hospital Rigshospitalet in Copenhagen reports an instance of a man whose muscle cell mitochondrial DNA matched that of his father rather than his mother.  This, however, is quite rare. (New England Journal of Medicine, vol 347, pp 576-580)]

diagram of mitochondria and mitochondrial DNA

Image courtesy of National Human Genome Research Institute [Public domain], via Wikimedia Commons

As the fertilized egg divides repeatedly to produce the trillions of cells of the human body, the mitochondria also divide and pass down their bit of maternal DNA to every cell in the body of the offspring. 

Since each cell contains thousands of mitochondria and each mitochondrion contains as many as one hundred copies of mitochondrial DNA, that means that each cell contains thousandsof copies of mitochondrial DNA but only one paired set of chromosomal DNA. This is why more mitochondrial DNA than chromosomal DNA can be obtained from smaller amounts of tissue.

What is Mitochondrial DNA?

Katie Barnes, BritainsDNA, 2015 Feb 12, What is Mitochondrial DNA? [Video file], retrieved from https://youtu.be/c_o4WQDbdOg

electron micrograph of mitochondria

Mitochondria are extremely small (from .002-.008 millimeters in length) rice-shaped structures whose details can only be seen with the electron microscope. The mitochondria shown in the figure to the left are from a mitochondria dense region of a visual cell.  A single mitochondrion in the lower right is outlined in yellow.  Mitochondria are often called the “powerhouses” of the cell because they are the site where sugar is broken down to release the energy required for cellular functions. 

A cell may have hundreds or even thousands of mitochondria depending on the particular cell’s need for energy. (For example, the average human liver cell contains more than a thousand mitochondria.) 

mitochondria diagram showing mitochondrial DNA

Image courtesy of National Human Genome Research Institute [Public domain], via Wikimedia Commons

In addition to containing the many proteins needed to control the energy release process, the mitochondria also contain a small amount of circular DNA that is used to direct the manufacture of thirteen of the proteins needed for its activities. Mutations in the protein coding part of mitochondrial DNA can cause some human diseases, typically involving either neuromuscular dysfunction or some forms of diabetes. 

Recent evidences show that mitochondria are also involved in other crucial functions such as cell signaling, cellular differentiation and cell death.

All Mitochondria Are Maternally Inherited
descendancy chart showing path of mitochondrial inheritance

All of an individual’s mitochondria are derived from his/her mother.  Although the sperm cell tail is packed with mitochondria to power its long journey to the egg cell, the tail and mitochondria drop off of the sperm at fertilization and do not enter the egg cell.  Sperm mitochondria that do happen to make it into the egg, are actively destroyed as soon as fertilization is complete. Consequently, all of the mitochondria in the fertilized egg come from an individual’s mother. 

[A 2002 publication by Marianne Schwartz and John Vissing from the University Hospital Rigshospitalet in Copenhagen reports an instance of a man whose muscle cell mitochondrial DNA matched that of his father rather than his mother.  This, however, is quite rare. (New England Journal of Medicine, vol 347, pp 576-580)]

As the fertilized egg divides repeatedly to produce the trillions of cells of the human body, the mitochondria also divide and pass down their bit of maternal DNA to every cell in the body of the offspring. 

Since each cell contains thousands of mitochondria and each mitochondrion contains as many as one hundred copies of mitochondrial DNA, that means that each cell contains thousandsof copies of mitochondrial DNA but only one paired set of chromosomal DNA. This is why more mitochondrial DNA than chromosomal DNA can be obtained from smaller amounts of tissue.

What is Mitochondrial DNA?

Katie Barnes, BritainsDNA, 2015 Feb 12, What is Mitochondrial DNA? [Video file], retrieved from https://youtu.be/c_o4WQDbdOg

Where Can I Go From Here?

Contexo.info is a not for profit, educational website.

©️2002 - 2017 Context.info

Where Can I Go From Here?

©️2002 - 2017 Context.info

Contexo.info is a not for profit, educational website.