Reduced forms of bacterial “ endosymbionts” that live
and replicate within our cells
Evolution of mitochondria is explained on the basis of
9. Mitochondrial DNA
A typical cell has about 100 mitochondria.
mtDNA is circular molecule .
When engulfed ,endosymbiont(mitochondria) lost almost
all genes because they were not needed
10. mtDNA retain some essential genes.
mtDNA contains 16569 bp
11. It resembles with a plasmid.
It is controlled by nuclear DNA.
It is made up of two strands . outer heavy and inner
Both strands have gene of replication.
13. Different regions on mtDNA prduce different proteins .
mitochondria show different expression in different
mtDNA shows Hetroplasmy
14. Replication of mtDNA
Mitochondria show d-loop replication.
Replication starts at replication site of H strand.
As it reaches another region of replication at L strand it
starts to circle in opposite direction.
16. In case of mtDNA stop codons are AGA , AAG
In case of nuclear DNA we have UAA ,UAG ,UGA
IN mtDNA UGA codes for tryptophan
mtDNA shows high mutation rate.
It does not show proof reading activities as observed in
case of DNA replication.
Lot of mutations take place during replication scheme
Mutageneic effects like oxidents, free radicles.
18. Inheritance of mtdna
mtDNA follows maternal inheritance.
Means it is always contributed from mother to offsprings.
The mitochondrial genome is circular, whereas the nuclear genome
is linear (Figure 3).
The mitochondrial genome is built of 16,569 DNA base pairs,
whereas the nuclear genome is made of 3.3 billion DNA base pairs.
The mitochondrial genome contains 37 genes that encode 13
proteins, 22 tRNAs and 2 rRNAs
The 13 mitochondrial gene-encoded proteins all instruct cells to
produce protein subunits of the enzyme complexes of the
oxidative phosphorylation system, which enables mitochondria to
act as the powerhouses of our cells.
The small mitochondrial genome is not able to independently
produce all of the proteins needed for functionality; thus,
mitochondria rely heavily on imported nuclear gene products.