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Prokaryotic Cell Structure

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The Prokaryotic CellMajor Structures

Cytoplasmic membrane

Cell wall

Cytoplasm

Inclusions

Nucleoid

Glycocalyx

Flagella

Pili & fimbrae

Endospores

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The Cytoplasmic MembraneOverview

~ 8 nm thick

Completely surround the

cell

Establishes the integrity ofthe cell

Selective barrier

Contains integral

membrane proteins Highly ordered yet

relatively fluid (fluid

mosaic)

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Cytoplasmic MembraneThe Phospholipid Bilayer

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Cytoplasmic MembraneUnit Membranes

Ectothiorhodospira halochloris photosynthetic membrane stacks

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The Cytoplasmic MembraneStructure

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The Cytoplasmic MembraneFunction

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The Cell Wall of Prokaryotes

Provides shape, rigidity

Keeps bacterial cells from lysing due to

internal turgor pressure

Two major types

Gram-negative: multilayered, complex

Gram-positive: single layer, thicker

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Cell Walls of Bacteria

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The Gram-Positive Cell Wall

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The Cell Wall of ProkaryotesThe Gram-Negative Outer Membrane

A second lipid layer

Contains polysaccharide

and protein

Lipid and polysaccharidelinked to form

lipopolysaccharides

Often called the

lipopolysaccharide layeror LPS.

Lipid A = endotoxin

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The Gram-Negative Cell Wall

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The E. coliNucleoid

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Bacterial Flagella

Long, thinappendages free atone end and attachedto the cell at the other

end. ~ 20 nm in diameter

Flagellar arrangement Polar

Lophotrichous Perithrichous

Flagellin: proteinsubunit of flagella

Peritrichous

Polar

Lophotrichous

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Flagellar Arrangements

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Structure of the Prokaryotic Flagellum

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Bacterial Cell Surface StructuresFimbriae & Pili

Both structurally similar to flagella but not

involved in movement

Fimbriae

Much shorter than flagella

Inherited trait

Enable cell to adhere to surfaces, formpellicles or biofilms

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Bacterial Cell Surface StructresFimbriae & Pili

Pili

Similar structurally to fimbriae but longer

Only one or two per cell

Serve as receptors for certain viruses

Involved in the process of conjugation

Involved in attachment of certain pathogenic

bacteria to tissues

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Fimbrae & Pili

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E. coliPilus

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Bacterial Cell Surface StructuresCapsules & Slime Layers

Glycocalyx: the polysaccharide material lying

outside the cell

Capsule: a rigid, tight matrix that can exclude

particles Slime layer: easily deformed, does not exclude

particles, hard to see

Functions

Attachment of pathogens Protection from phagocytosis

Resistance to desiccation

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Bacterial Capsules

Acinetobactersp. (negative stain) Rhizobium trifoli

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Endospores

Differentiated cells formed

within the vegetative cell

(sporangium)

Highly resistant to heat,

drying, radiation, acids,

chemical disinfectants

Bacillus, Clostridium

Dormancy maintained for

long periods