Prokaryotic cells [Gr. Pro = Primitive & Karyon = Nucleus]
The prokaryotic cells such as Blue-green algae (cyanobacteria), bacteria, mycoplasma etc. are without organized nucleus and membrane bounded orgenelles. They have nucleic acid in the form of circular bacterial chromosomes called nucleoids. Histone proteins are absent.
They undergo amitosis.
The outer covering of the prokaryotes is three layered viz. –
-
- Outer layer
- Cell wall &
- Plasma membrane.
1 Outer layer : It is made up of glycocalyx (Polysaccharides). It is in the form of hard covering called capsule or soft covery called Slime layers.
2. Cell wall : It forms structural covering and it is strong due to peptidoglycan.
3. Plasma membrane : It is the innermost layer which is semipermeable. It is made up of proteins (lipoprotein), lipids and oligosaccharides. It is the site for respiration, photosynthesis, lipogenesis and metabolic activities.
The prokaryotes have mesosomes which are three-layered and primarily meant for respiration. Some autotroph prokaryotes have pigments in lamellae instead of plastids which perform photosynthesis and nitrogen fixation.
They cytoplasm of prokaryotes consists of cyanophycean granules, glycogen granules, phosphate granules, polyhyderoxybutret granules, sulphur granules, carboxysomes and gas vacuoles. Presence of 70S ribsomes which are made up of two subunits of 50S & 30S and their dimension is 14-15 x 20 nM. The genetic material is in the form of nacked DNA and some RNA. Histone proteins are absent. Examples – Members of Kingdom-Monera such as bacteria, cyanobacteria, Archibacteria, Mycoplasma, Actinomycetes etc.
