Lecture 2 Flashcards
What is a prokaryote.
A single-celled (unicellular) organism, that thrive in an extreme range of environments. Usually have a diameters of 0.5-5µm.
What are the most common shapes of prokaryotes?
- Cocci, spherical. They can occur singly, in chains, or in clusters.
- Bacilli, rod-shaped. Usually solitary, but sometimes arranged in chains.
- Spiral. corkscrew shaped, some resemble commas or loose coils.
Explain the cell wall in prokaryotes.
Occurs in nearly all prokaryotes, maintains cell shape, protects the cell and prevents it from bursting in a hypotonic environment.
What is the cell wall of bacteria made of?
Contains peptidoglycan, a sugary polymer (composed of modified sugars, cross-linked by short poly-peptides).
This molecular fabric encloses the entire bacterium and anchors other molecules that extend from its surface.
How do archael cell walls differ to bacteria?
They contain a variety of polysaccharides and proteins but LACK peptidoglycan.
What is a gram strain and how does it work?
A way to categorise many bacterial species according to the differences in their cell wall composition.
Samples are stained, which enters the cell and binds to the cells DNA. The structure of a bacterium’s cell wall determines the staining response.
A gram stain helped to identify which antibiotics would be needed as the presence of the outer membrane of gram-negative bacteria is essential for protection against the body’s immune system. Gram-negative bacteria tend to more resistant to antibitoics.
What does Gram-positive mean?
A response to a gram strain from bacteria with relatively simple cell walls composed of a thick layer of peptidoglycan and one phospholipid bilayer beneath.
Stains pink / purple.
What does gram-negative mean?
Bacteria that have less peptidoglycan and are more structurally complex. Has an outer membrane that contains lipopolysaccharides (carbohydrates bonded to lipids).
Has two phospholipid bilayers and a thinner cell wall in the middle.
Does not stain.
