introduction to microbio and bacterial cells Flashcards
how many Cellular organisms are there
2 cell types
Prokaryotes
Eukaryotes
Prokaryotes
Bacteria
Archaea
1-5µm
Haploid
Asexual reproduction
Unicellular
No true nucleus
Cell wall*
Eukaryotes
Fungi (yeasts)
Protozoa, Helminths
Slime moulds, Algae
10µm
Diploid *
Sexual reproduction*
Unicellular /multicellular
True nucleus
viruses
No cellular
Structure.
(Genetic material surrounded by protein)
Prions
No nucleic acid
(Pieces of infectious protein)
e.g. Bovine Spongiform Encephalopathy
Bacteria
Unicellular
Huge diversity:
size,
shape,
habitat & metabolism
Majority are harmless or even beneficial
Morphology
cell shape
size
motility
spore forming
Metabolism
use of energy sources/nutrients
Molecular characteristics
protein, lipid structure
sequence of gene encoding 16S RNA
Plasma (cytoplasmic) membrane in bacterial cells
Selectively semi-permeable barrier
Mediates nutrient transport
Site of secretion & respiration
Site of environmental response regulators
Cytoplasm in bacteria
Between plasma membrane & nucleoid
* Ribosomes – protein translation (70S: 50S & 30S subunits)
Inclusion bodies: Storage bodies Contain important nutrients (C,P,N,S)
No mitochondria! – (Energy production occurs on the cytoplasmic membrane)
No True Nucleus
Double-stranded DNA in bacteria
Not enclosed by a nuclear membrane
- Usually a single closed circular chromosome
- DNA is supercoiled
- 1 copy of each gene
Plasmids- bacteria
extrachromosomal ;small, circular dsDNA
- replicate independently of chromosome (multiple copies)
- Encode auxiliary functions
Prokaryotic cell wall- bacteria
An extremely important structure
-Protects from the environment
Provides rigidity, strength
Unique to bacteria ( makes an excellent drug target)
Composed of peptidoglycan cross-linked to form a mesh
Peptidoglycan structure
A glycan backbone made of a chain of sugar residues-
Each sugar is joined by a strong glycosidic bond.
Every other sugar is linked to a short peptide (chain of amino acids)
These peptide sidechains crosslink to a peptide on an adjacent glycan backbone.
A strong mesh like structure is formed- It is NOT a solid barrier
Mesh like structure allows molecules to pass in and out.
2 types of bonds make it strong and rigid
Glycosidic bonds and peptide bonds
Contains other components that contribute to pathogenicity
(lipopolysaccharide, lipoteichoic acids)
peptidoglycan (PG) structure
divide MOST pathogenic bacteria into 2 Groups
Gram positive: stain PURPLE
Gram negative: stain PINK
Gram positive: stain PURPLE
THICK (20-80nm) PG layer which constitutes 60-80% cell wall
-X-linked to form thick mesh
Eg- Staphylococcus aureus
Gram negative: stain PINK
THIN (1-3nm) PG layer which
constitutes 10-20% cell wall
- Surrounded by an outer membrane
Eg. E.coli
Lipoteichoic acids- Gram-positive cell walls
Teichoic acids bonded
to membrane lipids
Released by killed
bacteria during infection.
Trigger inflammatory
response
Teichoic acids-Gram-positive cell walls
Acidic polysaccharides
bonded to peptidoglycan
Transport metal cations
Periplasm-Gram-negative cell walls
Gel-like consistency
Contains proteins
Lipopolysaccharide-Gram-negative cell walls
Stabilises membrane structure
Strongly immunogenic
Extremely toxic to animal cells
Heat resistant
Outer membrane-Gram-negative cell walls
Impermeable to large molecules
Porins-Gram-negative cell walls
Water filled channels
Lipopolysaccharide (endotoxin)-Lipid A
Embedded in
outer membrane.
Toxic: ENDOTOXIN
Lipopolysaccharide (endotoxin)-Core polysaccharide
10 sugars linked to lipid A
Lipopolysaccharide (endotoxin)-O-specific polysaccharide
On surface of outer membrane.
Immunogenic
Important that lipopolysaccharides are not present in injectable medicines
Bacterial endospores
Tough outer coat-Multiple layers of proteins and peptidoglycans
Dehydrated Core-Cytoplasm and DNA
Tough:
Resistant to: UV radiation, Desiccation, Freezing, High temperature and
MOST disinfectants (highly impermeable)
Capsules & slime layers
Capsule: Firm, rigid hard to remove.
Slime layer: loose layer which is easier to remove
A Network of polysaccharides secreted outside of the peptidoglycan cell wall
Function:
Give protection
Aid attachment
Contribute to virulence
- Evade body defences
Fimbriae (P-pili)
Aid attachment to surfaces
e.g. some pathogenic E. coli
Hair-like structures composed of protein subunits
F-pili
Used in bacterial conjugation
Hair-like structures composed of protein subunits
