Micr2000 Module 1 Lecture 2: Cell Walls and Capsules

How do vaccines work?

Vaccines train the immune system to recognize specific pathogens so it can respond faster and more effectively upon future exposure.

How do bacterial/eukaryotic and archaeal membrane lipids differ?

Bacterial/eukaryotic lipids: ester linkages with fatty acids. Archaeal lipids: ether linkages with isoprene units and no fatty acids.

What is the primary structural component of bacterial cell walls?

Peptidoglycan

What is the main difference between Gram-positive and Gram-negative peptidoglycan layers?

Gram-positive: ~90% peptidoglycan; Gram-negative: ~10% peptidoglycan sandwiched between membranes.

How is peptidoglycan crosslinked in Gram-positive bacteria?

Via peptide interbridges.

How is peptidoglycan crosslinked in Gram-negative bacteria?

 The NH₂ group of DAP links to the COOH group of D-alanine on an adjacent chain.

What is the purpose of peptidoglycan crosslinking?

It aids in providing structural strength to the cell wall

WHat are the key components of Gram +ve cell walls?

90% Peptidoglycan, teichoic acids, and lipoteichoic acids (the things sticking out at the top)

What are the key components of Gram -ve cell walls?

Thin (10%) peptidoglycan layer, outer membrane with LPS (Lipopolysaccharides - the things that stick out), and the periplasmic space

What is the role of Lipid A in Lipopolysaccharide layer of G-ve Cell walls

it acts as an endotoxin which is very toxic to humans and triggers strong immune responses

Which part of LPS varies, and which part is conserved

the O-antigen varies, whilst the Lipid A and core polysaccharides are conserved.

What toxin is released by meningococci?

LPS

What is the periplasm

it is a gel-like space which exists between the cytoplasm and outer membranes housing the various proteins

What does the Gram-stain differentiate

Gram Positive Cell walls retain a purple/violet colour, whilst Gram negative cell walls lose it, resulting in a pink/red colour

What are acid-fast bacteria

They are bacteria which cant be stained using crystal violet. these must be stained red using acid fast stain (Ziehl-Neelson stain)

What is an S-layer

It is the most common cell wall amongst Archaea. It is a paracrystalline layer which provides structural support and rigidity

What is pseudomurein

It is a peptidoglycan-like substance found within archaea

WHAT are capsule layers

they are polysaccharide layers found on top of a cell wall which assist in attachment to surfaces as well as biofilm formation, immune evasion and dessication resistance