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PROKARYOTIC CELL

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.


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