Prokaryotes

Organisms are classified on the basis of cell structure of two categories namely the eukaryotes and prokaryotes. Prokaryotes are organisms which do not have a cell nucleus to store its DNA. Prokaryotes have very few cell organelles where by none of the membrane-bound organelles are surrounded by an envelope of two membranes.They have cell walls which is a thick layer of network of fibres outside of the cell membrane that provides strength and rigidity. These differ from eukaryotes which have a nucleus containing genetic information (DNA). Most prokaryotes are unicellular (single cells) but there are some that have life cycles with multi cellular stages. Bacteria (such as Escherichia coli), archaea and cynobacteria are prokaryotes. The prokaryotes typically has an average diameter size of cell ranging between 0.5-5µm. The DNA in prokaryotes are circular,naked and lies free in the cytoplasm. The prokaryotes have slightly smaller ribosomes, 70S ( about18nm diameter) as compared to eukaryotes, 80S (about 22nm diameter). No endoplasmic reticulum , mitochondria and chloroplasts are present in a prokaryote cell. Prokaryote cells moves with the help of flagella or cilia made of flagellin. Prokaryotes breed through asexual reproduction, usually either by budding or binary fission (simple division).