question_answer 46)

  Is extragenomic DNA present in prokaryotes and eukaryotes? If yes, indicate their location in both the types of organisms. 

Answer:

                  Yes, extragenomic DNA is present in both prokaryotes and eukaryotes.. In case of   eukaryotes, extragenomic DNA is present in two orgahelles,' e.g., plastids andmitochondria. Extrachromosomal DNA in Prokaryotes In case of prokaryotic cells, the extragenomic DNA is present in the form of plasmids. The plasmid are circular DNA molecules, which   confer certain unique phenotypic characters to the bacteria.                           One such character is antibiotic resistance to bacteria. The plasmid DNA is also used to" monitor bacterial transformation with foreign DNA. Bacteria transformation is the method of  sexual reproduction in bacteria. Extrachromosomal DNA in Eukaryotes Mitochondrial DNA (n-rf DNA) is usually circular. Mitochondrial DNA spans about 16,500 DNAbuilding blocks (base pairs) representing a small fraction of the total DNA in cells. mt DNA contains 37 genes, all of which are essential for normal mitochondrial functions. Thirteen of these genes provides instruction for making enzymes involved in oxidative  phosporylation.          Mitochondrial genes are among the estimated 20000-25000 total genes in the human Genome. Plastids These are small bodies found free in most plant cells and are of three typesleucoplast, chromoplast and chloroplast. These are double membrane bound structures fortrapping radiation and storage purpose.         It contains small, double stranded circular DNA molecules and ribosomes essential in synthesising certain proteins. As they both can synthesise proteins and replicate on their own they are known as semi-autonomous organelles.