Prokaryotic Cell Structure
Outer structures:
Glycocalyx (capsule)
Cell wall
LPS
Flagella
Pili/fimbriae
Inner structures:
Magnetosome
Endospore
Ribosomes
Nucleoid
Crystalline inclusions
Storage granules
Glycocalyx (capsule)
The polysaccharide material lying outside of the cell.
- If attached to cell and forms rigid layers – referred to as capsule
- If not attached to cell and easily deformed – referred to as slime
Often important in pathogenicity: attachment & avoiding immune response
Most capsules are polysaccharide, although some are composed of proteins
The reasons bacteria have ‘halos’ around them is that the cells are surrounded by
a ‘capsule’ – bacteria with the capsule cause severe disease, bacteria without it
don’t.
Flagella:
Many bacteria are motile. Motility is usually due to the flagellum
Flagella are long, thin proteinaceous appendages made up of protein sub-units
called flagellin.
One end of the flagella is attached into the cytoplasmic membrane of the cell.
Axial filaments (flagella) of spirochetes are arranged differently but are a similar
structure. Spirochaetal axial filaments are encased within the outer membrane,
giving rise to corkscrew motility, allowing penetration of viscous
substrates/tissues. Disruption of the outer membrane reveals filament structures.
, Flagella assembly:
Once the base has formed in the cytoplasmic membrane, other protein molecules
are self-assembled on this structural base one after another in a well-defined
order.
All the axial component proteins of the flagellum are synthesised in the cytoplasm
and transported through the long narrow central channel to the distal end of the
growing structure, onto which they self-assemble.
Flagellar Distribution:
Petrichous – twitching-moving-sensing (food source)
Polar
Outer structures:
Glycocalyx (capsule)
Cell wall
LPS
Flagella
Pili/fimbriae
Inner structures:
Magnetosome
Endospore
Ribosomes
Nucleoid
Crystalline inclusions
Storage granules
Glycocalyx (capsule)
The polysaccharide material lying outside of the cell.
- If attached to cell and forms rigid layers – referred to as capsule
- If not attached to cell and easily deformed – referred to as slime
Often important in pathogenicity: attachment & avoiding immune response
Most capsules are polysaccharide, although some are composed of proteins
The reasons bacteria have ‘halos’ around them is that the cells are surrounded by
a ‘capsule’ – bacteria with the capsule cause severe disease, bacteria without it
don’t.
Flagella:
Many bacteria are motile. Motility is usually due to the flagellum
Flagella are long, thin proteinaceous appendages made up of protein sub-units
called flagellin.
One end of the flagella is attached into the cytoplasmic membrane of the cell.
Axial filaments (flagella) of spirochetes are arranged differently but are a similar
structure. Spirochaetal axial filaments are encased within the outer membrane,
giving rise to corkscrew motility, allowing penetration of viscous
substrates/tissues. Disruption of the outer membrane reveals filament structures.
, Flagella assembly:
Once the base has formed in the cytoplasmic membrane, other protein molecules
are self-assembled on this structural base one after another in a well-defined
order.
All the axial component proteins of the flagellum are synthesised in the cytoplasm
and transported through the long narrow central channel to the distal end of the
growing structure, onto which they self-assemble.
Flagellar Distribution:
Petrichous – twitching-moving-sensing (food source)
Polar
