General microbio Flashcards
General description of a bacteria ?
- Small self replicating organism
- Prokaryotes
- no real nucleus
- No compartment of the cytoplasm - Total mass of the bacteria of human beings : approx 700g
What do organisms need to replicate?
Genetic material/information (DNA or RNA)
Need organelles to replicate (ribosomes)
- (Viruses have no ribosomes)
What are some differences between prokaryotes and eukaryotes?
Prokaryotes:
- Diameter of 1-5 um
- Have a nucleoid (something equivalent to a nucleus, but no membrane)
- They have plasmids (extra chromosomal DNA)
- 70S ribosomes
- Cell wall containing peptidoglycan
Eukaryotes:
- 5 um and larger
- Nucleus containing membrane
- 80S and 60S ribosomes
- Endoplasmic reticulum, golgi apparatus
- Lysosomes
- Mitochondria (70S ribosomes)
- Some have no cell wall, cell wall of fungi and plants always without peptidoglycan
Name some structures of the bacteria
Cytoplasm
Nucleoid
Ribosomes
Cell wall = > Cytoplasmic membrane + capsule
Pili
Flagella
Describe the capsule
- (Bacillus anthracis, Streptococcus equi subsp. equi. )
- Contains extracellular substances (glutamic acid, hyaluronic acid)
- Protection against dehydration
- Permeability barrer )e.g. antibiotics)
- Increasing adhesion
- Protection against phagocytosis (performed amongs other by macrophages and monocytes)
- biofilm
Give features of the flagella
- Motility of bacteria
- Makes Taxis possible (able to move)
- Can be indicator of virulence factor
- Antigens can be found on the flagella (can be used in the diagnosis/differenciation of bacteria. Ex: salmonella types)
- Powered by protons (1000 protons/rotation)
What type of taxis is the bacterial taxis?
Chemotaxis.
Can attract/repell
=> bacteria can move to attractant , move away from repellants
Name and describe 2 attachment structures
Fimbriae
- 20 um lon protein filaments
- 10-1000 per cell
- Adhesion organelles (adhesin)
- F-antigens
Pili
- Tubular hair-like protein structures
- 1-2 per cell
- F-pilus, sexpilus => conjugation
What is the function of the cell wall?
- Shaping exoskeleton
- Permeability barrier
- Adhesion to host cells
- Virulence factors
- Antigens
What is the matrix of the cell wall made of?
- Peptidoglycan, murein
- A peptidoglycan monomer is composed of : N-acetylglucosamin and N-acetylmuramic acid (NAM-NAG)
- Also additional cross-linkages through oligopeptide side chains
What is the difference between a gram - and gram + cell wall?
Gram +:
- Cytoplasmic membrane (phospholipid bilayer)
- Peptidoglycan (10-40 layers)
Gram -:
- Inner membrane (phospholipid bilayer)
- Peptidoglycan (1-3 layers)
- Outer membrane
- LPS (lipopolysaccharides)
In what type of bacteria do you find the LPS layer (lipopolysaccharide). Gram - or Gram +?
Describe this LPS layer and its implication in infections
Gram -
LPS has 3 parts:
- Lipid anchor (lipid A). Part of the outer membrane of the gram negative bacteria. Also is an endotoxin, pyrogen.
- A core region. 5 sugar molecules
- O-specific side chains. Repetitve unnits of oligosaccharides. O-antigens (somatic antigens). Are heat stable, serotyping.
As soon as the cell is destroyed (ex: antibiotics etc.), the lypopollysaccharides (toxin) is released and can harm the body. Therefore, an infection to a gram - bacteria can cause more trouble than infection to a gram + bacteria. (réécouter la slide sur le LPS)
Describe the nucleoid
- Bacterial chromosome
- Can be circular or linear
- Is double stranded
- Is free in the cytoplas, only few proteins (histones)
- Contains the housekeeping genes
- Mostly single copy genes: no compensation after mutation by homologous genes possible (so if mutation, cell dies/stops replicating)
- One of the model is E. Coli, has 1000 encoding genes
How does the nucleoid organize itself in the bacterial cell?
Explain
By supercoiling.
DNA Gyrases makes the DNA curl => topoisomerase II
What does the bacterial cell use to “relax” the supercoils?
Topoisomerase I
