Intro

Question 1

What distinguishes gram-negative bacteria from gram-positive bacteria?

Answer 1

Neg bacteria has an additional lipid bilayer made of lipopolysaccharides (LPS): this bilayer contains phospholipid in its inner leaflet and LPS in its outer leaflet, ie the otuer membrane is an asymmetric lipid bilayer.

It also has a periplasm

Question 2

What are the three domains in LPS molecules?

Answer 2

1. the lipid A structure which inserts LPS in outer leaflet of outer membrane bilayer
2. the covalently attached LPS core
3. the O-antigen, a polysaccharide chain that is linked ot the core

Question 3

What are Koch’s postulates?

Answer 3

1. The suspected pathogenic organism should be present in ALL cases of the disease, ABSENT from healthy animals
2. The suspected organism should be grown in pure culture.
3. Cells from a pure culture of the suspected organism should cause disease in a healthy animal.
4. The organism should be reisolated and shown to be the same as the original.

Question 4

Gram-stain technique?

Answer 4

crystal violet added to sample on slide, water wash

iodide solution added, water wash

destain with ethanol/acetone

safranin counterstain (red)

gram negative: red
gram positive: purple

Question 5

Describe the difference between cell walls of gram-positive and gram-negative

Answer 5

thick cell wall, mostly made of peptidoglycan (murein) in gram positive

gram negative is very thin

Question 6

What is the structure of peptidoglycan?

Answer 6

1) crystal lattice of two alternating amino sugars: N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc)
2) each disaccharide contains a tetra or pentapeptide sibstituent of alternating L adn D amino acids
3) peptide bridges link the terminal COOH of D-alanine of one tetrapeptide to an NH2 group of a tetrapeptide on a neighboring glycan chain

Question 7

how do bacterias sense the environment?

Answer 7

EnvZ: histidine kinase

Question 8

What are two ways bacteria can be mobile? Which is recognized by the immune system?

Answer 8

pili, flagella (recognized–“flagellin protein”)

Question 9

What is superantigen?

Answer 9

Superantigens: an exotoxin that binds to the T cell receptor and MHC but NOT through the antigen-binding domain so that any T cell can be stimulated, regardless of its specificity. As a result, you have an over-activated immune system, which is eventually depleted

Question 10

How do gram positive bacteria primarily adhere to cell surfaces (colonization)? What about gram negative bacteria?

Answer 10

Positive: Teichoic acids: primary mechanism of gram-positive cells

Negative: pili/fimbriae

Question 11

Peptidoglycan synthesis:

The peptidoglycan monomers are synthesized in the _____ and are then attached to a membrane carrier ______. This carrier transports peptidoglycan monomers across the cell membrane where they are inserted into the existing peptidoglycan. They are first added to a linear chain, in a process called ____. Then they are cross-linked to an adjacent chain, in a process called ____.

Answer 11

The peptidoglycan monomers are synthesized in the cytosol and are then attached to a membrane carrier bactoprenol. Bactoprenol transports peptidoglycan monomers across the cell membrane where they are inserted into the existing peptidoglycan.

They are first added to a linear chain, in a process called transglycosylation. Then they are cross-linked to an adjacent chain, in a process called transpeptidation.

Question 12

What is the function of bactoprenol?

Answer 12

The function of bactoprenol is to render sugar intermediates sufficiently hydrophobic so that they will pass through the hydrophobic cytoplasmic membrane.