Week 5

Today's Topics:
○ Prokaryote Cell Biology

Lecture Topic:
During the lecture, take notes here.
○ Viable count calculation checker on WebCT
○ Average adult has approximately 1014 cells.
○ 10% of these are human cells
○ 10% are bacteria
○ Bacteria on skin prevent colonisation by pathogens.
○ Approx 2000 people die per year in UK from undiagnosed infections.
○ Some bacteria have multiple chromosomes - most eukaryotes have linear chromosomes.
○ Plasmids are rare in eukaryotes - yeast has one.
○ Flagella
§ Movement is termed motility - something that can move is motile.
§ Bacteria swim in straight lines - flagella in cooperation - if not in cooperation, bacteria tumble.
§ Flagella arrangements:
□ Single, at one end, or at both ends - polar
□ All over cell - peritrichous
§ Not all species are motile - flagella are not universal.
§ Protein
○ Pili
§ Generally found in gram-negative bacteria
§ Allow bacterium to adhere to solid surfaces (e.g. in alimentary canal)
§ Sex pilus allows transfer of genetic bacteria (covered in detail in genetics II)
§ Protein
○ Capsule / slime layer
§ A matter of degree - a slime layer is a thin capsule
§ Thickness varies by species and environment
§ Protects cell from desiccation
§ Allows cell to adhere to solid surface
§ Allows cell to evade immune system - resists phagocytosis.
§ Generally associated with pathogens.
§ Protein and/or Carbohydrate
○ Cell wall
§ Found in almost all species
§ Gram staining depends on nature of cell wall.
§ Gram positive cells homogenous 20-80 nm wall.
§ Gram negative cell walls in layers:
□ Outer membrane - 8-10 nm
□ (periplasmic space) - widely variable or absent
□ Rigid layer - 1-3 nm
§ Peptidoglycan is only in bacteria, not in eukarya or archea. (aka mucopeptide).
§ PG made of n-acetyl glucosamine & n-acetyl muramic acid - alternating units in linear chains, cross-linked with short proteins, (about 10aa), in a 3d mesh.
§ Teichoic Acid - mixture of sugar alcohols, cross-liked with phosphates
§ Lipopolysaccharides - often toxic, and can be cause of symptoms of gram negative infections. - trigger immune response.
○ Plasma membrane
§ Much the same as in eukaryotes
§ Energy generation is carried out on PM, as no mitochondria.
○ Mesosome
§ Infolding of membrane to increase area for energy generation.
○ Storage Granules
§ Volutin - phosphorus store - stained pink by methylene blue
§ Polysaccharides - iodine stains starch blue , glycogen red-brown
§ Also sulphur, gases
○ Endospores - survival mechanism - allow cell to survive adverse conditions (not reproduction)