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.

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.

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