IMPORTANT POINTS
Lacks a well defined nucleus i.e. Nuclear envelope is absent.
The circular double stranded genetic material (Nucleoid) floats in the cytoplasm of the cell.
Chromatin, nucleolus, histone proteins are absent.
Packing of DNA is performed by positively charged Polyamines.
Lacks membrane bound cell organelles like mitochondria, plastids, ER etc.
Ribosomes of 70S types are present.
Gas vacuoles/ Pseudovacuoles are present.
Size is smaller than eukaryotic cells.
Single envelope system is present.
STRUCTURE OF A PROKARYOTIC CELL
PARTS OF A PROKARYOTIC CELL
CELL ENVELOPE
Made up of 3 layers:
Glycocalyx
Gelatinous layer made up of carbohydrates
Exists in 2 forms in prokaryotes i.e. Slime layer and Capsule.
SLIME LAYER
Present as a loose sheath
Prevents dessication ofthe cell.
CAPSULE
Tightly attached to the cell wall.
Protects bacteria from immune system of the host
Responsible for the pathogenicity of the bacteria.
CELL WALL
Archaebacteria have the cell wall made up of Psuedopeptidoglycan (Polymer of N-acetylglucosamine and N-acetyltalosaminuronic acid)
Eubacteria cell wall is made up of Peptidoglycan. (Polymer of N-acetylglucosamine and N-acetylmuramic acid)
Mycoplasma lacks a cell wall.
CELL MEMBRANE
The structure of the cell membrane is same as that in Eukaryotic cells.
CELLULAR PROJECTIONS
FLAGELLA
Made up of helically arranged Flagellin protein
Helps in locomotion
PILI
Made up of Pilin protein
Longer, less in number
Helps in transfer of DNA from one bacteria to another (Conjugation)
FIMBRIAE
Made up of Pilin protein
Short, more in number
Helps in attachment to a surface
NUCLEOID
Also known as Incipient nucleus/ Genophore/ Prochromosome
Double stranded circular DNA is the genetic material in prokaryotes
Prokaryotic genome has high G-C content
MESOSOME
Formed by invagination of the cell membrane
Helps in Respiration, DNA replication, cell division, secretion of substances etc.
CHROMATOPHORES
Pigment containing structures
Present in photosynthetic bacteria and Blue-Green Algae
PLASMID
Extra-chromosomal, self-replicating, circular ds DNA
Provides additional features to the cell eg. Antibiotic resistance
RIBOSOMES
70S type of ribosomes are present in prokaryotes
Made up of two sub-units- 50S and 30S
Performs the function of protein synthesis
INCLUSION BODIES
Aggregates of molecules present in prokaryotic cell
Acts as storage structures
Types- Starch granules, glycogen granules, gas vacuoles etc
gas vacuoles
A type of inclusion body
Also known as Pseudovacuoles.
Present in photosynthetic bacteria and Blue-green algae.
Provides bouyancy to the cell.
Watch the video here :-