Bacterial Physiology Peptidoglycan Biosynthesis

Glycan chains are crossed-linked by:

peptides

Peptidoglycan is made up of:

glycan chains

Glycan consist of:

Alternating residues of NAG and NAM

NAG and NAM are attacked to each other by

Beta 1,4 glycoside bonds

NAM stands for

N-acetylglucosamine

NAM stands for

N-acetylmuramic acid

What type of network does the peptidoglycan structure allow:

a mesh like network

What type of bonds does the cross linking of structure form?

Covalent

Where is the peptidoglycan layer located?

Surrounds the cell membrane

What gives the cell wall its strength?

Covalent bond, the give the cell wall its rigidity and strength

The peptidoglycan is a _____________ molecule

very large

What can destroy the cell wall?

lysosome or antibiotics

What happens when the peptidoglycan wall is destroyed?

It can create weak spots in the cell, swelling can then occur and cause lysis due to internal turgor pressure

Where are the bonds on NAG and NAM?

C1 bond of NAM and C4

_______ is a modified structure of __________

NAM is a modified version of NAG

How is NAM modified?

Lactyl group attached to the C3 carbon

_______ is attached to each NAM

tetrapeptide

Tetrapeptide is:

L-alanyl-D-Glutamyl-gamma-L-R3-D-alanine

What can change on the tetrapeptide within different bacterial species:

The position of the 3 carbon, it can be L or R

What is this structure of?

Structure of peptidoglycan

What is the red structure of?

NAG

What is the green structure of?

NAM

What is the orange structure of?

The tetrapeptide

Tetrapeptide are cross linked by

peptide bonds

Peptide bridge in peptidoglycan:

The D-alanine in one tetrapeptide to a amino acid in the L-R3 position in another tetrapeptide

Gram negatives have a _______ cross-linking

Direct

Why do gram negatives have a more direct cross link?

Because their peptidoglycan is thinner

What is the linkage between in gram negative

D-alanine and diaminopimelic acid

What other species is a direct cross-linking seen in?

Bacillus species

Crosslinking in gram positive

The have a bridge of one or more amino acids and the thickness varies in each species

How many residues in Staphylococcus

5 glycine residues

How many residues in micrococcus roseus

3 L-alanine and 1 L-threonine

How many residues in staphylococcus epidermidis

3 glycine and 2 L-serine

Functions of peptidoglycan:

Helps maintain the shape of the cell wall and responsible for cellular morphogenesis

Where is lysozyme found and what does it do?

Found in tears, saliva, breast milk, and mucus. It hydrolyzes the glucosidic linkages

What antibiotics target the peptidoglycan:

Penicillin, vancomycin, and bacitracin all infer with the synthesis

Peptidoclyxqn protects cells from lysis in ________ solutions

Hypotonic

First step of peptidoglycan synthesis:

precursors are UDP derivatives of the amino sugars made in the cytosol

Second step of peptidoglycan synthesis:

Amino sugars are transferred to a lipid carrier in the membrane

Third step of peptidoglycan synthesis:

Peptidoglycan is polymerized in the outer surface of the membrane

Fourth step of peptidoglycan synthesis:

Transpeptidation reaction cross-links the peptidoglycan

NAG and NAM are made up of

Fructose-6-phosphate

What are the sugars of peptidoglycan

NAG and NAM

Glutamine donates what during UDP derivatives synthesis?

An amino group

What does the fructose-6-phosphate convert to after reviving an amino group?

Glucosamine-6-phosphate

How is NAG-6-P created?

Transacylase transfers an acetyl group to the amino group on glucosamine-6-phosphate.

NAG-6-phosphate is isomerized to:

NAG-1-P

How is NAG-6-P isomerized?

Mono phosphate attacks UTP and displaces the pyrophosphate to form UDP-N-acetylglucosamine (UDP-GlcNAc)

What then happens to some the UDP-GpcNAc

Converted to UDP-N-acetylmutamic acid (UDP-MurNA )

How is UDP-GlcNAc converted to UDP-N-acetylmutamic acid (UDP-MurNAc)

Addition of a lactyl group to the sugar

How is enol pyruvate created?

C3 hydroxyl or the sugar displace the phosphate from the alpha carbon of phosphoenolpyruvate

What is is enol pyruvate?

Derivative of UDP-MurNAc

What then happens to enol pyruvate?

Reduced to the lactyl moiety by NADPH

What is UDPMurNAc then converted to:

To UDP-MurNAc pentapeptide

How is UDP-MurNAc pentapeptide created

Sequential addition of amino acids: L-alanine, D-glutamate l, L-R3, dipeptide D-alanyl-D-alanine, ATP

What does the reaction of UDP-MurNAc to UDP-MurNAc pentapeptide require?

ATP

Why does UDP-MurNAc need ATP for its reaction?

To activate the carboxyl group of the amino acid and allows for the displacement of phosphate

What are the products of the conversion of peptidoglycan synthesis?

UDP-MurNAc Pentapeptide, ADP, and inorganic phosphate

What enzymes are used to create D-alanine-D-alanine?

Racemase ans synthetase

Racemase:

Concerts L-alanine to D-Alanine

Synthetase:

Makes D-alanine-D-alanine from 2 D-alanines

What inhibits synthesis of D-alanine-D-alanine

Cycloserine

UDP-MurNAc Pentapeptide is then transferred to the:

Lipid carrier in the membrane

Lipid carrier:

Bactroprenol, or lipid P

Lipid A serves as a:

Carrier for peptidoglycan precursors and other components of the cell wall

Nucleotide sugars defuse the membrane by:

Lipid P attacks UDP-MurNAc pentapeptide displacing UMP and produces lipid-PP-MurNAc (pentapeptide)

GlcNAc is transfered from ___________ to _______________

UDP-GlcNAc to the MurNAc on the lipid carrier

How is the GlcNAc transferred?

C4 hydroxyl in the MurNac attacks the carbon in UDP-GlcNAc displacing the UDP

Disaccharide precursor to peptidoglycan is produced and move to:

Lipid-PP-MurNAc-GlcNAc and moves to the other side of the membrane

What then happens to the lipid disaccharide?

Transferred to the growing end of the acceptor glycan chain

How is the lipid disaccharide transferred to the growing end?

Transglycosylation reaction; the C4 hydroxyl of the incoming GlcNAc attacks the C1 of the murNAc in the glyan and displace lipid-Pp from the growing glycan chain

The growing glycan chain remains anchored to the membrane by:

lipid carrier at the site of transglycosylation

Lipid-PP is released by and produces:

Released by membrane bound pyrophosphatase and produces Lipid-P and Pi

Lipid-PP is important bc:

drives transglycosylation to completion

_________ regenerates Lipid-P

Hydrolysis

Why is hydrolysis of Lipid-P important?

Necessary for continuing the growth of the peptidoglycan

Hydrolysis of Lipid-PP is inhibited by:

bacitracin

Transpeptidation

provides the energy necessary to make the peptides cross-link outside the cell membrane

Transpeptidation is inhibited by:

Penicillin

How does peptide cross-linking work?

NH2 from the diamino acid in position 3 attacks the carbonyl carbon in the peptide bond holding the 2 D-alanine residues and displaces the terminal D-alanine and results in a new bond

PBP:

penicillin binding proteins and they are membrane proteins found in the peptidoglycan of bacteria

What do PBP do?

Catalyze the transglycosylation and transpeptidation steps and some are required for peptidoglycan synthesis in the septum