MCB Lecture 44 Introduction to Bacteria I Flashcards
What is the average size of a bacterium?
1-2 microns
List the general features of bacteria
Size: 1-2 microns No membrane bound organelles Smaller ribosomes Single, circular piece of DNA Cell wall made of peptidoglycan
Compare organelles in eukaryotic and prokaryotic cells
Prokaryotic cells have no membrane bound organelles
Describe the genetic component of prokaryotic cells, including location and structure
Single, circular piece of dsDNA
Genetic material is located in the nucleoid, there are also RNA and protein
Plasmids can also be present in the cytosol
What are plasmids?
Describe how they replicate, and their presence in a cell
These are small fragments of DNA present in a loop
They are not replicated at the same time as the chromosome
They use the bacteria’s machinery to replicate
They are variable in size and number
Describe the features of a bacterial cell wall.
One or two plasma membranes
Layer of peptidoglycan
Describe the process of the gram stain
- Purple stain
- Wash
- Lipid solvent wash
- Counter stain
- Wash
- Lipid solvent
Why is the Gram stain useful?
It categorises a bacterium into either G+ or G-
We can tell much about a bacterium through this classification
Describe the structure of a G+ bacterium cell wall
One plasma membrane surrounded by a thick layer of peptidoglycan
Much more simpler than G-
Less protective, has pores
Describe the structure of a G- bacterium cell wall
Inner and outer membrane, sip which surround a thin layer of peptidoglycan
Much more complex than G+
The outer membrane forms a protective barrier, that only allows small molecules and glucose in
Antibiotics and bile salts are excluded
Complex secretory systems are required
LPS found on the outer membrane
Describe the structure of Peptidoglycan
Alternating “bricks” of N-acetyl glucosamine and N-Acetyl muramic acid
Peptide chains: different amino acids
These connect the sugar to the pentapeptide bridges
Alternating D and L amino acids –> prevents flexibility
Rigid structure of peptidoglycan
Pentapeptide bridges: same amino acids
Connect to the peptide chains
What is LPS?
Where is it found?
Lipopolysaccharide
It is a molecule that is always found on the outer membrane of gram negative bacteria
What is the function of LPS?
- Endotoxin: it is a major PAMP recognised by the innate immune system
- It is vital for the integrity of bacterial cell walls
Which type of bacteria (G- or G+) has a more protective barrier in its cell wall
G-
What is an endotoxin?
It is a toxin produced by a bacterium that is not released into the environment, but instead localised in or on the bacterium