gram staining

Question 1

what does gram staining do ?

Answer 1

distinguishes between two groups of bacteria based in the structures of their walls

Question 2

what do all bacteria have in their cell walls?

Answer 2

peptidoglycan

Question 3

what can some bacteria have in their walls

Answer 3

lots of mesh and others have a thicker layer

Question 4

describes the step for gram staining

Answer 4

1. crystal violet stain is added and is taken up by peptidoglycan
2. iodide added to fix stain to the peptidoglycan
3. ethanol added to wash away membranes
4. safronnin is added as a counterstain which enables any unstained cells to be visible put in a different colour(pink)
5. Gram negative = Pink
   Gram positive = remains purple

Question 5

Describe gram nevative

Answer 5

thinner layer of pepdidoglycan surrounded by an outer membrane
antibiotic must cross cell wall to be effective
reduced ability of penecillin to cross the outer membrane
less distruption of cell wall / pepdidoglycan synthesis
cell walls are rigid and prevent wxcess of water entry
cells dont busrt
cells continue to grow around the disc of penecillin so there is no zone of inhibition

Question 6

describe gram positive

Answer 6

thick layer of peptidoglycan
no outer membrane - penecillin can enter
penecillin prevents cross linking of protein chains in the peptidoglycan by inhibiting and enzyme
therefore cell wall sunthesis is distributed
new cells grow abnormally
cant maintain their wall rigidity
cells burst due to take up of water by osmosis
no growth around the disc
penecillin prevents growth of nerve cells

Question 7

how do antibiotics kill bactera

Answer 7

stopping synthesis of cell wall

Question 8

why cant antibiotics kill gram negative bacteria

Answer 8

have an external membrane that protects peptidoglycan cell wall