<prompt> Function of mitochondrial DNA -Encodes proteins of cell membraneEncodes proteins of respiratory chainHelps in cell replicationFormation of rRNA  <response>: Ans. is b i.e., Encodes proteins of respiratory chain o Human mitochondria contain two to ten copies of a small circular double-stranded DNA molecule that makes up approximately 1 of total cellular DNA. The majority of the peptides in mitochondria about 54 out of 67 are coded by nuclear genes. The rest are coded by genes found in mitochondrial mt DNA.This mtDNA codes for mt ribosomal and transfer RNAs and for 13 proteins that play key roles in the respiratory chain.Some Major Features of the Structure and Function of Human Mitochonrial DNAo Is circular, double-stranded, and composed of heavy H and light L chains or strands,o Contains 16,569 bp.o Encodes 13 protein subunits of the respiratory chain of a total of about 67 -y Seven subunits of NADH dehydrogenase complex Iy Cytochrome b of complex IIIy Three subunits of cytochrome oxidase complex IVy Two subunits of ATP synthaseo Encodes large 16S and small 12S mt ribosomal RNAso Encodes 22 mt tRNA moleculeso Genetic code differs slightly from the standard code -y VGA standard stop codon is read as Trp.y AGP and AGG standard codons for Arg are read as stop codons,o Contains very few untranslated sequences,o High mutation rate 5 to 10 times that of nuclear DNA.o Comparisons of mtDNA sequences provide evidence about evolutionary origins of primates and other species. 