- Cells having membrane bound nuclei
- Each cell have an outer membrane as a delimiting structure of cell.
- They have membrane bound cell organelles like Endoplasmic reticulum, Golgi complex, Lysosomes, Mitochondria, Microbodies and Vacuole.
- Cells having membrane bound nuclei
- The cell envelope consists of a tightly bound 3 layered structure that act together as a single protective unit and their plasma membrane have modifications like mesosome and chromatophore.
- The prokaryotic cells lack such cell organelles.
➢In both prokaryotic and eukaryotic cells, a semi-fluid matrix called Cytoplasm occupies volume of the cell.
➢The Cytoplasm is the main arena of cellular activity.
➢Animal cells contain another non membrane bound organelle called centrosomewhich help in cell division.
➢Prokaryotic DNA is more stable than Eukaryotic DNA.
➢Shape of the is variable, It depends on the function performed by the cell.
➢ Nerve cells are the longest cells.
➢The largest isolated single cell is the egg of an ostrich.
➢Human RBC - 7.0um in diameter
➢Bacteria – 3 – 5um
➢Smallest cells – Mycoplasma – 0.3um in length
➢The prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO (pleuropneumonia like organisms).
➢All filamentous prokaryotes are multicellular.
➢These are generally smaller, primitive with simple organization.
➢They multiply more rapidly than the eukaryotic cells
➢These cells doesn't have Compartmentalization, membrane bound cell organization,cytoskeleton, 9+2 arrangement.
➢The DNA of these cells is haploid, double standard, circular and naked.
➢True nucleus is absent, Incipient nucleus/Genophore is present.
➢Histone proteins and true chromosomes are absent.
➢70S ribosomes are present.
➢These cells have cell wall surrounding cell membrane except in mycoplasma.
➢The cytoplasm is the fluid filled matrix.
➢In addition to genomic DNA many bacteria have small extracellular double standard circular DNA called plasmid.
➢Plasmid do not have vital role in metabolism, but it contains some helpful gene.
➢These plasmid DNA confers certain unique phenotypic characters to such bacteria.
Example:
- Antibiotic resistance gene
- Nitrogen fixation gene
➢On basis of difference in cell envelope and response to staining bacteria can be classified into 2 types,
- Gram positive bacteria – bacteria which take up gram strain
- Gram negative bacteria – bacteria which doesn't take up gram strain
➢The cell envelope of prokaryotic cells consists of tightly bound three layered structure i.e.,
➢Outermost layer
➢
Composition: Glycolipid, Glycoprotein (carbohydrate + protein + lipid).
It could be as
- slime layer – loose sheath
- capsule – thick and tough
➢ It is the middle layer.
➢ It determines the shape of the cell.
➢ It provides structural support and prevent the bacterium from bursting or collapsing.
➢ Present in all except mycoplasma.
➢ Composition : N-acetyl glucosamine(NAG) and N-acetyl muramic acid(NAM).
➢ Selectively permeable and it is similar in structure to eukaryotes.
➢ Composition : Phospholipid
➢ These 3 layers act together as a single protective unit but each layer has a different function.
➢ Photosynthetic pigments are trapped in infoldings of plasma membrane.
➢ It is present in only photo autotrophic bacteria.
➢ FUNCTION : As chloroplast in bacteria.
➢ Photosynthetic pigments are trapped in infoldings of plasma membrane.
➢ It is present in only photo autotrophic bacteria.
➢ FUNCTION : As chloroplast in bacteria.