Lecture 2- Cell walls of bacteria and archaea Flashcards
what are two prokaryotes that lack cell walls?
mycoplasmas
thermoplasma
what are mycoplasmas?
group of pathogenic bacteria
without a cell wall how do mycoplasmas keep themselves together?
have sterols in cytoplasmic membrane which add strength and rigidity to the membrane
what are thermoplasmas?
species of archaea
how do thermoplasmas keep themselves together?
contain lipoglycans in membrane that have a strengthening effect
what are characteristics of outside the cell membrane? (4)
rigid (determines cell shape)
not a major permeability barrier
porous to most small molecules
protects cell from osmotic changes (hard to break cell)
what are the 4 functions of the cell wall?
- prevents cell expansion (protects against osmotic lysis)
- protects against toxic substances
- pathogenicity (helps evade host immune system and helps bacterium stick to surface)
- partly responsible for cell shapes
what is the big difference between gram negative cell wall and gram positive cell wall?
gram negative has two layers (peptidoglycan and LPS)
gram positive has one layer (peptidoglycan)
is gram (+) or (-) thicker with peptidoglycan?
positive (90% of walls are peptidoglycan)
what is peptidoglycan?
rigid layer that provides strength to cell wall
what is peptidoglycan made of?
N- acetylglucosamine acid
N- acetylmuramic acid
amino acids
lysine or DAP
explain the structure of peptidoglycan
contains two sugars NAM and NAG which are connected by glycosidic bonds, cross links are formed by peptides(amino acids), peptides are held together by gly- gly- gly- gly- gly
what is a common thing to have in gram positive cells (what acidic substance)?
teichoic acids and lipoteichoic acid (lipid+teichoic acid)
does gram negative or positive have an interbridge?
gram positive (gly- gly- gly- gly- gly)
how much of gram negative cell wall is peptidoglycan?
~10% (peptidoglycan is a lot thinner in gram (-)
what is the cell wall of gram negative mostly made up of?
lipopolysaccharide (LPS)
what does LPS do?
replaces most of phospholipids in outer half of outer membrane
what does the structure of LPS contain?
O- polysaccharide
core polysaccharide
lipid A
what is the toxic component to LPS?
lipid A
what is the periplasm?
space located between cytoplasmic and outer membranes (~15nm wide, contents have gel- like consistency)
what is the function of the periplasm?
house many proteins
what are porins?
channels for movement of hydrophilic low molecular weight substances
what happens in a gram stain?
in gram stain reaction, insoluble crystal violet- iodine complex forms inside cell
how does crystal violet work on gram negative bacteria?
crystal violet- iodine is extracted by alcohol, alcohol penetrates outer membrane, CV-I gets extracted from the cell, cells appear nearly invisible until counterstained with second dye (safrin)
how does crystal violet work on gram positive bacteria?
crystal violet- iodine stain doesn’t work because of the thick peptidoglycan therefore with alcohol step, pores in wall close and prevent CV-I from escaping
do archaeal cell walls have peptidoglycan?
no
what do archaeal cell walls have instead of peptidoglycan?
pseudomurein
what is pseudomurein composed of?
composed of N-acetylglucosamine acid and
N- acetyltalosaminuronic acid
what is pseudomurein?
polysaccharide similar to peptidoglycan (similar in chemical makeup)
do all archaea have pseudomurein?
no
what do archaeal cells have in their cell walls if they don’t have pseudomurein?
S- layers (dont need any other cell components) but most cells do
what do S- layers consist of?
protein or glycoprotein
what kind of structure are S- layers?
paracrystalline structure
because archaeal cell walls don’t have any peptidoglycan, what are they resistant to?
lysozyme and penicillin
what does the structure of the cell walls in archaea function to do?
functions to prevent osmotic lysis and give shape
