Bacteria Basics

Question 1

what is peptidoglycan? key property -> reason for this property?

Answer 1

2D network of alternating NAG (N-acetylglucosamine) and NAM (N-acetylmurine) subunits. Hydrophilic, so it can exclude damaging hydrophobic compounds ie bile salts.

Question 2

what are lipotechoic acids? function?

Answer 2

Sugar alcohol (ie ribitol or glycerol) polymers linked via phosphodiester bonds. Embedded in murein. 
Function: adhere to surfaces

Question 3

Basic structure of Gram+ vs Gram- bacteria

Answer 3

Gram+: outer layer is thick murein with embedded techoic/lipotechoic acids. In between the murein & the phospholipid bilayer cell membrane is the periplasmic space, which hosts enzymes.

Gram-: outer LPS membrane, then periplasmic space, then thin murein layer, then periplasmic space, then inner phospholipid bilayer

Question 4

Structure of LPS

Answer 4

(inner)
1) Lipid A (“endotoxin”) embeds the LPS to the bacteria
2) Core polysaccharide
3) O-antigen (repeating hydrophilic hydrocarbons, vary with species)
(outer)

Question 5

Bacterial capsules: structure? G+ or G-? 3 functions?

Answer 5

AAs or sugars, both G+ and G- may have them.

1) Prevent dessication
2) Defends against immune attack (ie phagocytosis)
3) Determines ability to colonize a niche

Question 6

Pili (fimbriae)- most common in G+ or G-? 2 roles?

Answer 6

Common in G-, rare in G+.

1) attach to surfaces
2) cause movement via waves of contractions/releases

Question 7

What are carboxysomes?

Answer 7

Bacterials vesicles that fix CO2

Question 8

What are exotoxins? Typical structure & action?

Answer 8

Secreted by bacteria. Typically an A-B structure, where the B subunit binds a eukaryotic receptor & gets endocytosized, and the A unit is then released to the cytoplasm.

Question 9

Type III cytotoxins: how do they work? 5 examples?

Answer 9

Bacteria have a Type III “secretory injection system” to inject them directly into eukaryotic cells
Salmonella, Shigella, Pseudomonas, cholera, Yersinia pestis (plague)

Question 10

3 types of surface-acting toxins

Answer 10

1) bind PRRs
2) pore-forming
3) “super-antigens”: bind TCRs/MHC

Question 11

Cholera: what sort of toxins? Exotoxin structure? How does it work, briefly?

Answer 11

A+5B exotoxin (& Type III cytotoxins too). Elevates intracellular cAMP in small intestinal epithelia, moves fluid to lumen.

Question 12

Diphtheria: what sort of exotoxin structure? Action?

Answer 12

AB. ADP-ribosylates eEF-2 (an elongation factor) to block cell protein synthesis

Question 13

Anthrax: what sort of exotoxin structure?

Answer 13

2A-B

Question 14

Endotoxin: 4 cellular targets, effects at low concentration?

Answer 14

1) Kuppfer cells: increase IL1 & TNF, producing fever via cytokine release from macrophages
2) Neutrophils: increases kinins, producing vasodilation
3) B lymphocytes: Ab increase
4) Complement: activate the alternate pathway, producing inflammation