Lecture 2- Cell walls of bacteria and archaea

Question 1

what are two prokaryotes that lack cell walls?

Answer 1

mycoplasmas
thermoplasma

Question 2

what are mycoplasmas?

Answer 2

group of pathogenic bacteria

Question 3

without a cell wall how do mycoplasmas keep themselves together?

Answer 3

have sterols in cytoplasmic membrane which add strength and rigidity to the membrane

Question 4

what are thermoplasmas?

Answer 4

species of archaea

Question 5

how do thermoplasmas keep themselves together?

Answer 5

contain lipoglycans in membrane that have a strengthening effect

Question 6

what are characteristics of outside the cell membrane? (4)

Answer 6

rigid (determines cell shape)
not a major permeability barrier
porous to most small molecules
protects cell from osmotic changes (hard to break cell)

Question 7

what are the 4 functions of the cell wall?

Answer 7

1. prevents cell expansion (protects against osmotic lysis)
2. protects against toxic substances
3. pathogenicity (helps evade host immune system and helps bacterium stick to surface)
4. partly responsible for cell shapes

Question 8

what is the big difference between gram negative cell wall and gram positive cell wall?

Answer 8

gram negative has two layers (peptidoglycan and LPS)
gram positive has one layer (peptidoglycan)

Question 9

is gram (+) or (-) thicker with peptidoglycan?

Answer 9

positive (90% of walls are peptidoglycan)

Question 10

what is peptidoglycan?

Answer 10

rigid layer that provides strength to cell wall

Question 11

what is peptidoglycan made of?

Answer 11

N- acetylglucosamine acid
N- acetylmuramic acid
amino acids
lysine or DAP

Question 12

explain the structure of peptidoglycan

Answer 12

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

Question 13

what is a common thing to have in gram positive cells (what acidic substance)?

Answer 13

teichoic acids and lipoteichoic acid (lipid+teichoic acid)

Question 14

does gram negative or positive have an interbridge?

Answer 14

gram positive (gly- gly- gly- gly- gly)

Question 15

how much of gram negative cell wall is peptidoglycan?

Answer 15

~10% (peptidoglycan is a lot thinner in gram (-)

Question 16

what is the cell wall of gram negative mostly made up of?

Answer 16

lipopolysaccharide (LPS)

Question 17

what does LPS do?

Answer 17

replaces most of phospholipids in outer half of outer membrane

Question 18

what does the structure of LPS contain?

Answer 18

O- polysaccharide
core polysaccharide
lipid A

Question 19

what is the toxic component to LPS?

Answer 19

lipid A

Question 20

what is the periplasm?

Answer 20

space located between cytoplasmic and outer membranes (~15nm wide, contents have gel- like consistency)

Question 21

what is the function of the periplasm?

Answer 21

house many proteins

Question 22

what are porins?

Answer 22

channels for movement of hydrophilic low molecular weight substances

Question 23

what happens in a gram stain?

Answer 23

in gram stain reaction, insoluble crystal violet- iodine complex forms inside cell

Question 24

how does crystal violet work on gram negative bacteria?

Answer 24

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)

Question 25

how does crystal violet work on gram positive bacteria?

Answer 25

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

Question 26

do archaeal cell walls have peptidoglycan?

Answer 26

no

Question 27

what do archaeal cell walls have instead of peptidoglycan?

Answer 27

pseudomurein

Question 28

what is pseudomurein composed of?

Answer 28

composed of N-acetylglucosamine acid and
N- acetyltalosaminuronic acid

Question 29

what is pseudomurein?

Answer 29

polysaccharide similar to peptidoglycan (similar in chemical makeup)

Question 30

do all archaea have pseudomurein?

Answer 30

no

Question 31

what do archaeal cells have in their cell walls if they don’t have pseudomurein?

Answer 31

S- layers (dont need any other cell components) but most cells do

Question 32

what do S- layers consist of?

Answer 32

protein or glycoprotein

Question 33

what kind of structure are S- layers?

Answer 33

paracrystalline structure

Question 34

because archaeal cell walls don’t have any peptidoglycan, what are they resistant to?

Answer 34

lysozyme and penicillin

Question 35

what does the structure of the cell walls in archaea function to do?

Answer 35

functions to prevent osmotic lysis and give shape