Procaryotic cell structure

Procaryotic cell structure

Simple cells compared to eucaryotic structure – more primitive without a true nucleus.

Cytoplasm:
Similar to eucaryotic cells; predominantly aqueous with ribosomes and nucleotide-protein complexes

Cytoplasmic particles:
Nuclear body/bacterial nucleoid:
• single long chromosome; double stranded DNA
• exists in a ‘supercoiled’ structure (~1mm in length if extended)
• may have additional fragments of DNA (episomal DNA) – often called plasmids

Ribosomes:
• consists of protein and RNA; smaller than eukaryotic cells
• concerned with protein synthesis

Cytoplasmic inclusions:
• various

Cell membrane:
• as bacteria have limited cell organelles, the cell membrane carries out many of the functions
• 5-10nm thick; relatively weak
• consists mostly of phospholipids and proteins

Cell wall:
• external to cell membrane; 10-25nm thick; relatively strong structure
• rigid structure that protects cell from rupture (high osmotic pressure in cell)
• porous and permeable to low molecular weight substances
• plays important role in cell division
• generally two types – gram positive and gram negative

Gram positive cell walls:
Less complex than gram negative. Has thick layer (15-80nm) of peptidoglycan (murein, mucopeptide) arranged on a rigid meshwork.

Gram negative cell walls:
Peptidoglycan layer is only 1-2nm. Has two membranes – outer lipoprotein layer and an inner cytoplasmic membrane seperated by the periplasmic space

Capsules:
Layer of extracellular gelatinous material, mostly polysaccharides.
Function to help bacteria adhere to tissues and resist ingestion by phagocytosis

Flagella:
Long threadlike appendages made up of the protein, flagellin.
Allow motility of bacteria by rotation

Pili/Fimbriae:
Filamentous appendages on many bacteria that extrude from the cytoplasmic membrane
Composed of the protien, pilin

Spores/endospores:
Formation of spores is how some microorganisms survive harsh environmental conditions
Genetic material of cells is concentrated and surrounded by a protective coat  becomes very resistant to desiccation, heat and many chemical agents.
Spores are biochemically inert

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Page last updated: @ 7:58 pm