 |
| The human mitochondrial genome. (Schon et al. 1997) |
As we know,
mitochondria are cytoplasmic organelles exclusive for eukaryotes. They have the central role of oxidative energy metabolism to the viability of the cell. Mitochondria
contain a small specialized genome and a complete process of gene expression
for their particular activities, distinct from that of the cell nucleus and
cytosol. In humans, the mitochondrial genome is constituted by a circle of
double-stranded DNA with 16, 569 base pairs. This circle DNA is highly compact
and contains only 37 genes: 2 genes encode ribosomal RNAs, 22 encode transfer
RNAs, and 13 encode polypeptides. The 13 polypeptides are components of the
respiratory chain, the oxidative phosphorylation system (Schon et al. 1997).
The
female egg contains a cytoplasm with many mitochondria and other organelles.
Besides the nuclear DNA, it has the entire mitochondrial DNA, which has the
same genetic information for all mitochondria. The sperm has mitochondria placed where
they can most efficiently control the flagellum, providing energy for their
movement. In the fertilization, the only genetic material that the embryo
inherits from the male is from the nuclear genetic material contained in the
head’s sperm. Therefore, the individual inherits all the genetic mitochondrial
material from the female, contained in the egg. In resume, we have the same
genetic mitochondrial material and mitochondrial phenotype as our mother.
Studies
in evolutionary biology analyze mitochondrial inheritance to identify the
degree of proximity between populations and species. Allen and de Paula (2013)
also suggest that the contributions of male/female for the mitochondria arose
with the evolutionary origin of separate sexes. This knowledge is also useful in cases whereby
a child mother is not known, and then tests with mitochondrial DNA may be done
to prove if a woman is the birth mother. Another importance is observed in
studies about human disorders. Pathogenic mutations in the mitochondrial genome
can have devastating consequences; one of these is respiratory chain deficiency.
REFERENCES
Allen J. F.
& de Paula W. B. M. (2013). Mitochondrial genome function and maternal
inheritance. Biochemical Society
Transactions 41(5) 1298-1304.
Schon, E. A.; Bonilla, E; DiMauro
S. (1997). Mitochondrial DNA Mutations and Pathogenesis. Journal of Bioenergetics and Biomembranes, 29(2) 131-149.
I find the transmission of mitochondrial DNA down the maternal line to be absolutely incredible! This neatly explains the concept of Mitochondrial Eve. Can you elaborate more on what respiratory chain deficiency is? Interesting read.
ReplyDeleteThe respiratory chain (RC) provides oxidative phosphorylation and ATP synthesis, supplying most organs and tissues. Therefore, RC deficiencies can theoretically cause any symptom, in any organ or tissue, at any age and with any mode of inheritance, because RC components have genetic origin from nuclear DNA and mitochondrial DNA. It is difficult to diagnose RC deficiencies, they are usually identified when two unrelated symptoms are observed. The most common symptoms are neuromuscular and renal problems. It is common glomerular disease and metabolic acidosis. Urinary losses of amino acids, glucose, proteins, ions, and water are generally observed. Renal biopsies demonstrate anomalies of the tubular epithelium, non-differentiation or atrophy, and occasionally giant mitochondria (Rötig &Munnich, 2003).
ReplyDeleteRötig &Munnich (2003). Genetic Features of Mitochondrial Respiratory Chain Disorders. Jornal of the American Society of Nephrology. 14 (12). p 2995-3007.