Mitochondrial inheritance

Mitochondrial Inheritance
Apart from the nucleus DNA is also found within another cellular organelle, the mitochondrion.
Each mitochondrion contains multiple copies of a double-stranded, circular DNA molecule of 16,569 base pairs.
This DNA has 37 genes out of which encodes 13 peptides that are subunits of proteins required for oxidative phosphorylation.
There is a complete set of 22 transfer RNAs and two ribosomal RNAs.

1. MITOCHONDRIAL INHERITNCE HARSHITA SHARMA 190014155003 MSc. Biotechnology  

2. THE MITOCHONDRIAL GENOME: Apart from the nucleus DNA is also found within another cellular organelle, the mitochondrion. Each mitochondrion contains multiple copies of a double-stranded, circular DNA molecule of 16,569 base pairs. This DNA has 37 genes out of which encodes 13 peptides that are subunits of proteins required for oxidative phosphorylation. There is a complete set of 22 transfer RNAs and two ribosomal RNAs.

3. The structure of the mitochondrial genome bears more resemblance to prokaryotic than to eukaryotic genomes. The genes lack introns and are transcribed as polycistronic messages from two promoters. The spaces between genes consist of tRNAs, whose excision from the polycistronic message releases the individual gene transcripts. There are also two sites for initiation of DNA synthesis, one on each strand of the double helix.

4. PATTERN OF INHERITANCE: A number of clinical disorders have been identified that are due to mutations within mitochondrial genes. As might be expected, these traits are associated with failure of mitochondrial energy production. Mitochondrial DNA exhibits two critical differences from the nuclear genome that account for unusual patterns of inheritance of mitochondrial genetic traits. These are: MATERNAL TRANSMISSION HETEROPLASMY

5. MATERNAL GENETIC TRANSMISSION: The trait is transmitted from a mother to all of her children, but is not transmitted by males. This is due to the fact that essentially all of the mitochondria are maternally inherited. At the time of fertilization only, the sperm nucleus enters the egg. Mitochondria in the sperm are shed prior to fertilization. There may be minor exceptions to this rule but, for the most part, mitochondrial traits are maternally inherited .

6. Maternal genetic transmission. An affected woman transmits the trait to all of her children. Affected men do not pass the trait to any of their offspring.

7. HETEROPLASMY: Unlike the nuclear genome, which is represented by one complete copy per cell, there are hundreds of mitochondrial DNA molecules in each cell. These mitochondria separate passively when a cell divides, in contrast to the orderly separation of chromosomes in the nuclear genome during cell division. If some of the mitochondria contain a mutation and others do not, the result can be unequal distribution of mutant and nonmutant mitochondria to daughter cells.

8. MITOCHONDRIAL DISORDERS: Mitochondrial diseases can arise through mutation in mitochondrial DNA or mutation in nuclear DNA which encodes mitochondrial protein. Mitochondria are responsible for the generation of adenosine triphosphate (ATP) via aerobic metabolism and tissues which consume high energy such as brain tissues, heart, skeletal muscles can be severely affected. Mitochondrial genetic disorders caused by mutations in nuclear DNA may follow an autosomal dominant, autosomal recessive, or X-linked pattern of inheritance.

9. SYNDROMES:

10. MELAS: MELAS (MIM 540000) is an acronym for mitochondrial encephalomyopathy , lactic acidosis, and stroke-like episodes. The disorder may present at any time in life with progressive neurological deterioration and seizures. There are events in which there is sudden onset of neurological deficit that have the time course of strokes. Lactic acid tends to accumulate in the blood, especially during stroke-like episodes. Lactic acid is a byproduct of the failure of aerobic metabolism in the mitochondria. Various mitochondrial mutations can be responsible for MELAS. The most common is a mutation in the mitochondrial gene for leucine tRNA (MIM 590050).

11. MERRF: Myoclonic epilepsy with ragged red fibers (MERRF) is a multisystem disorder characterized by myoclonus, which is often the first symptom, followed by generalized epilepsy, ataxia, weakness, and dementia. Symptoms usually first appear in childhood or adolescence after normal early development. The features of MERRF vary widely from individual to individual, even within families. Other common findings include hearing loss, short stature, optic atrophy, and cardiomyopathy with Wolff-Parkinson-White (WPW) syndrome. clumps of diseased mitochondria accumulate in the subsarcolemmal region of the muscle fiber and appear as "Ragged Red Fibers" when muscle is stained with modified Gömöri trichrome stain

12. REFERENCES: Hartwell and Goldberg, From genes to genomes/Patterns of inheritance https://rarediseases.info.nih.gov/ www.ncbi.nlm.nih.gov

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