INTRODUCTION
Genome is the sum total of all genetic material of an organism. The genome may be either DNA or RNA. Eukaryotes and prokaryotes always have a DNA genome but viruses may either have a DNA genome or RNA genome. There are two distinct parts in eukaryotic genome, one is the nuclear genome and the other is the organelle genome, which is of two types: mitochondrial and chloroplast genome respectively.
This paper focuses on the organelle genome of eukaryotes, that is, mitochondrial and chloroplast genome. Mitochondria are found in both animals and plants, whereas chloroplast is found only in plants.
It was believed that these two organelles were two different, individual living entities. But these organelles were engulfed by a different
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It is free from chromosomal proteins which is present in eukaryotic chromosomal DNA. The size of mtDNA varies among organisms as shown in the table below:
ORGANISM SIZE (kb)
Homo sapiens (human) 16.6
Mus musculus (mouse) 16.2
Xeropus laevis (frog) 18.4
Drosophila melanogaster (fruit fly) 18.4
Saccharomyces cervisiae (yeast) 75.0
Pisum sativum (pea) 110.0
Arabidopsis thaliana (mustard plant) 367.0
The mtDNA is smaller in animals than in plants as seen in humans it is only 16.6 and in plants it can be as big as 367. Introns are not present in mitochondrial genes and gene repetition hardly occurs.
Human mtDNA codes for two ribosomal RNA (rRNA), twenty two transfer RNA (tRNA) and 13 polypeptides which are essential for the oxidative respiration functions of the organelle. As mentioned earlier there are two strands in the mtDNA, these strands vary in density, as was proven by centrifugation. The two strands are the heavy (H) and the light (L) strands. Most of the genes are encoded by the H strand and some by the L strand.
All vertebrate mtDNA is very similar to that of humam, most of the noncoding regions of DNA are concentrated in one