Micro - The Bacterial Cell Flashcards
Why aren’t antibiotics harmful to humans?
Antibiotics target bacterial cell walls which human cells do not have which is why it does not affect human cells.
What is the difference between gram-positive and gram-negative bacteria?
The cell wall. Gram-positive bacteria have a thick peptidoglycan wall (30-100nm) and lack an outer membrane. Gram-negative bacteria have thin peptidoglycan walls (few nm).
What colour does gram-negative bacterium stain? Why?
Pink. The thin wall does not retain the crystal violet very well.
What colour does Gram-positive bacterium stain?Why?
Purple. The thick cell wall retains crystal violet well.
What is the purpose of the cell wall?
- Protective armour, prevents damage to the cell and penetration of bacterial viruses.
- Exoskeleton, keeps the cells from.
- Prevents osmotic lysis (bacteria can be transferred to different solutions for example dropped into water, they need to be able to adjust to the conditions and prevent swelling and lysis.
What is an adhesin?
Virulence factors that allow bacteria to stick to a host cell.
What type of bacteria is less susceptible to antibiotics? why?
Gram-negative due to the outer membrane, It slows and prevents the entrance of antibiotics.
LPS?
Lipopolysaccharide. The outside of the outer membrane (gram neg). It has variable surface antigens so it can evade the immune system. Contains Lipid A (endotoxin) which can send the immune system into overdrive by activating immune responses like macrophages. Can cause septic shock.
What are porins?
Transmembrane proteins in the outer membrane which are large channels allowing for passive diffusion of small hydrophilic molecules (and antibiotics).
What is the function of a capsule?
Immune invasion - too slippery for macrophages to attach to.
Can be an adhesin and help the bacteria stick to the host.
Not all bacteria have capsules PATHOGENIC FEATURE.
What ribosomes do bacteria posses?
70s. (50s large + 30s small subunits).
Bacterial ribosome drug target.
The bacterial ribosome is a very important antibiotic target. Specific antibiotics interact with regions of rRNA.
PLASMID
- Carry antibiotic resistant genes.
- Conjugative (can transfer resistance genes to donor plasmids)
- (NHR) Narrow Host Range can only be maintained in a single bacterial host.
- (BHR) Broad Host Range can replicate in multiple unrelated bacteria. (worse for humans)
PLASMIDS
They are classified according to similarities in replication.
plasmids with similar replication systems are members of the same inc group and cannot coexist in the same cell)
TRANSPOSONS
Jumping genes. A segment of DNA capable of moving from one site to another causing mutation by inserting or disrupting genes and can carry resistance genes.
