Prokaryotic vs Eukaryotic DNA
All the organisms are classified as either Prokaryotic or Eukaryotic. The Organisms that lack nucleus or membrane bounded organelles are called prokaryote while eukaryotes have ‘true’ nuclei that contain DNA and membrane bound organelles. Eukaryotes may be unicellular or multicellular organisms. DNA (DeoxyriboNucleic Acid) is a nucleic acid that contains the genetic information, which are used in the development and functioning of all living organisms (exception RNA viruses). In the DNA, the sequences carrying the genetic information are called genes, other sequences are for structural purpose or to regulate the genetic information.
Bacteria are the well known example for prokaryote. Even though, most of the prokaryotes are unicellular, a few have multicellular stages in their life cycle. Generally, prokaryote’s cytoplasm contains ribosome and nucleoid with strands of irregular DNA. There is only a single loop of DNA present in the nucleoid. It does not have histone protein and occurs as a circular chromosome.
All the animals, plants, and fungus are eukaryotic organisms; nuclear envelope is the most defining character for all eukaryotic organisms. In eukaryotes, mostly DNA is stored inside the cell nucleus, but some are found within the organelles such as chloroplasts and mitochondria. Histone protein and organized DNA are compacted inside the chromosome.
In living organisms, DNA exists as a pair of molecules that are held tightly together and form a double helix structure.
Structurally DNA consists of two long polymers made from repeating units, which are called nucleotide. The backbone of the DNA strand is made by the alternating phosphate sugar residues. That sugar is 2-deoxyribose, which is five –carbon sugar called as pentose. Each sugar is joined together by phosphate group that forms the phosphodiester bond between third and fifth carbon atoms of adjacent sugar rings. In double helix structure, the nucleotide’s direction in one strand is opposite to their other stand direction (i.e. anti-parallel). The asymmetric ends of the DNA strands consist 5’ (five prime) and 3’ (three prime) ends where 5’ end has a terminal phosphate group, and the 3’ end has a terminal hydroxyl group. The DNA double helix is stabilized by hydrogen bonds between nucleotides and base-stacking interactions among the nucleobases. There are four bases found in DNAs such as adenine (A) cytosine (C), guanine (G), and thymine (T). A and G are called purines and C and T are called pyrimidine. These four bases bind to the sugar or phosphate and form the complete nucleotide. Each nucleobase on one strand interacts with one type of nucleobase in the other strand. The purines form the hydrogen bonds to pyrimidine. Here, A bonds only to T by two hydrogen bonds, and C bonds only to G by three hydrogen bonds.
What is the difference between Prokaryotic DNA and Eukaryotic DNA?
• In eukaryotes, DNA is found mostly in the cell nucleus, but some are in mitochondria and chloroplast while, in prokaryotes, it is found in the cytoplasm.
• DNA usually occurs as circular chromosomes in Prokaryotes while it is linear chromosomes in Eukaryotes.
• Eukaryote DNA has the histone protein, but prokaryote doesn’t have that.
• Prokaryotes contain only a single loop of chromosomal DNA, whereas Eukaryote DNA is found on tightly bound and organized chromosomes.
• In Prokaryotes, many important genes are stored in satellite DNA, which is referred as plasmid, but only some of the eukaryotes have this plasmid.