Week 4

Question 1

What does the most popular antibiotic target?

Answer 1

The cell wall

Question 2

What does B-lactam target?

Answer 2

The cell wall

Question 3

Do call prokaryotes have an outer membrane

Answer 3

No, just gram negatives

Question 4

What are the roles of the cell envelope

Answer 4

• controls entry and exit
• protection

Question 5

What is the cytoplasmic membrane composed of, characterisitic?

Answer 5

Lipid bilayer:
- its lipid composition depends on conditions (ex.temp)
- protein-rich

Semipermeable membrane:
- water and hydrophobic substances diffuse thru
- hydrophilic substances do not

Question 6

What is the main component of the bacterial cytoplasm?

Answer 6

the bacterial cytoplasm is mainly phospholipids

Question 7

What type of bond attaches fatty acids to glycerol?

Answer 7

ester bonds

Question 8

Define: Ampiphatic

Answer 8

Amphipathic: polar and non-polar regions

Question 10

Name 3 functions of cytoplasmic membrane proteins

Answer 10

Transporters:
- import and export substances

Signal Transduction:
- detect external stimuli

Energy Transduction:
- ETC to generate proton motor force (PMF)
- PMF powers ATP synthesis, transport …

Question 11

Bacteria are usually in a ______ environment:
a) hypotonic
b) hypertonic
c) isotonic

Answer 11

Bacteria are usually in a hypotonic environment
- they have more solutes in the cell than there are in the environment

Question 12

What is the major component of the cell wall?

Answer 12

peptidoglycan

Question 13

What makes gram neg diff from gram positive

Answer 13

gram neg
- thin cell wall
- inner and outer membrane

Question 14

What are 3 features of PG

Answer 14

1) Strong
- determines cell shape
- protects against osmotic lysis

2) Elastic
- stretches, contracts in response to osmotic pressure

3) Porous, mesh-like
- let in/out nutrients and waste

Question 15

What is the consequence of the PG being distrupted

Answer 15

if PG is disrupted, the cell becomes more susceptible to osmotic lysis in a hypotonic environment

Question 16

What happens if bacteria lose PG in an isotonic environment?

Answer 16

They loose shape:
Spheroplast = gram neg
Protoplast = gram pos

Question 17

Case - Mycoplasmas

Answer 17

Mycoplasmas
- small pleomorphic bacteria
- lack cell wall thus osmotically sensitive so live in others cells, isotonic environment

Question 18

Why is PG a good antibiotic target?

Answer 18

• on or near surface
• made by most bacteria
• no made by human cells

Question 19

Name 2 antibiotics that target PG

Answer 19

• B-Lactam
• Vancomycin

Question 20

Describe the PG structure

Answer 20

• made of sugars and aa
• backbone is a long glycan strand with repeating NAM and NAG disaccharide units
• every NAM bears a peptide chain
• glycan strands are connected to each other thru peptide cross links

Question 21

What is Lipid II, and what does it contain?

Answer 21

Lipid II: key precursor of PG
- contains monomeric PG subunit (NAM and NAG)
- bound to membrane by UDP

Question 22

How does lipid II synthesis start?

Answer 22

Lipid II synthesis starts with UDP-NAG, UDP activates NAG

Question 23

REMINDER: See steps for lipid synthesis on ipad

Answer 23

DO it

Question 24

What does “alanine racemase” make?
What does D-ala-D-ala ligase make?
What inhibits these?

Answer 24

D-Ala
D-Ala-D-Ala
Cycloserine (antibiotic)

Question 25

Penicillin Binding Protein (PBP)
- Purpose
- Location
- Needed for:
Domain:

Answer 25

Penicillin Binding Protein (PBP)
Purpose: incorporates Lipid II into PG
Location: periplasm
Needed for:
- cell growth
- cell division
- cell wall recycling
Domain: has a glycosyltransferase domain makes glycan strands, peptide cross links

Question 26

What does the PBD glycosyltransferase domain do?

Answer 26

the glycosyltransferase domain adds lipid II disaccharide to the glycan backbone of PG

Question 27

Lysozyme
- function/what does it
- define
- more effective against …

Answer 27

Lysozyme

PG glycan backbone can be degraded by:
- bacterial enzymes for cell wall remodeling
- antimicrobial enzymes

Lysozyme: part of innate immune system
- saliva, tears, milk, mucous
- weaken cells wall

Lysozymes are more effective against gram-positives
- PG is more exposed
- gram neg have outer membrane

Question 28

Describe the PG peptide chain

Answer 28

-pentapeptide attached to NAM sugar
- amino acid sequence varies
- contains D-aa
- Diamino acid in the 3rd position

Question 29

Described PG-cross linking in gram negatives

Answer 29

• gram negs form a cross link btwn the 3rd residue (diamino acid) and the 4th residue (carbonyl)
• for a amide bond
• release terminal D-alanine

Question 30

Described PG-cross linking in gram negatives

Answer 30

• gram positives form peptide chains cross linked thru interpeptide bridge
• bridge is attached to diamino acid
• release terminal D-alanine

Question 31

Describe the mechanism of Transprptidation

Answer 31

• Cross links are formed by PBP transpeptidase domain

1) PBP forms a complex with peptide
2) diamino acid reacts with complex, forms amid bond

Question 32

What antibiotic targets the transpeptidase domain?

Answer 32

B-Lactam

Question 33

B-lactam Antibiotics … What?

Answer 33

B-Lactams: penicillin’s, cephalosporins, carbapenems
- most widely used antibiotic

Question 34

B-lactam mechanism

Answer 34

• inhibits PBP transpeptidase activity
• B-lactam ring reacts with seine in PBP
• blocks PBP from forming cross links, thus weakens PG leading to cell lysis
• bacteriocidal