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Biology - Microbiology > Structure - Peptidoglycans > Flashcards

Structure - Peptidoglycans Flashcards

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1
Q

What is the function of peptidoglycans?

A

Maintenance of cell shape and preservation of cell integrity, resisting turgor.

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2
Q

What is the general structure of peptidoglycans?

A

Linear glycan strands with peptide stems cross0linked by short peptides.

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3
Q

What are glycan strands composed of ?

A

N-acetylglucosamine and N-Acetylmuramic acid linked by 1-4 bonds.

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4
Q

Where are the cross linkages found?

A

On the amino stems that substitue on MurNAc residues.

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5
Q

Where do the variations in PG exist?

A

Peptide stem, glycan strands and composition of interpeptide bridge.

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6
Q

What is an example of PG differentiation?

A

In Staphyloccus Aureus where the reducing end of the glycan contain either MurNAc or GlcNAc.

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7
Q

Why is coupling of PG cell wall with essential functions important in medicine?

A

It makes it a good target for antibiotics.

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8
Q

Where is the PG wall found in GNB?

A

The periplasm between OM and IM.

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9
Q

What is the structural differences of the PG cell wall in GNB and GPB?

A

In GNB it is a monolayer, whilst GPB it has multiple.

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10
Q

Why does GPB have a thicker PG?

A

As it lacks an OM thus is exposed to external environment.

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11
Q

What are the two additional structural constituents of GPB?

A

Teichoic Acids and Mycolic Acids

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12
Q

Teichoic Acids

A

These contribute to surface charge and hydrophobicity, affecting binding of extracellular molecules.

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13
Q

Mycolic Acids

A

Long chain FA important in virulence and viability.

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14
Q

What is the function of myolic acids?

A

Impede chemical entry, causing slower growth in organisms with more resistance to chemical agents.

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15
Q

What drives shape generation?

A

Asymmetric PG synthesis driven by cytoskeltal elements.

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16
Q

What is the first step of PG synthesis?

A

Cytoplasmic stage where the UDP-N-AcetylMurNAc precursor and UDP-N-Acetylglucosamine precursor are synthesised.

17
Q

What is the second stage of PG synthesis?

A

Cytoplasmic membrane stage where precursors form lipid intermediates; Phosphate MurNAc transfers to bactoprenol yielding Lipid 1, with addition of UDP-N-Acetylglucosamine forming Lipid II.

18
Q

Bactoprenol

A

This cycles PG monomers through the PM, inserting them at points of growth in the cell wall in GPB.

19
Q

Why is bactoprenol lipophilic property important?

A

Enables cell to transport hydrophilic precursors from aqueos environment of the cytoplasm through the hydrophobic membrane.

20
Q

What is the third stage of PG synthesis?

A

Outer side of cytoplasmic membrane where LipidII is polymerised, incorporating into growing PG, facilitated by PBP.

21
Q

Pencillin Binding Proteins

A

These catalyse transglycolysation and transpeptidations reactions responsible for formation of glycosidic and peptide bonds on the pg.

22
Q

Teichoic Acids

A

These are anionic polymers within GPB cell walls, composed of repeating glycerol or ribitol phosphate polymers.

23
Q

What is the function of Teichoic acids?

A

Structural integrity with negative charged phosphates.

24
Q

Mycolic Acids

A

These are long-chain fatty acids found in lipid-rich cell walls of mycobacteria.

25
Q

What are the functions of mycolic acids?

A

Immunoreactions
Form wax-like layer to protect against nvironmental stressors.

26
Q

What are the functions of the PG CELL WALL?

A

Support/rigidity, osmotic pressure resistance and host immune system interaction.

27
Q

What is the first step in PG synthesis?

A

The precursor UDP-bound NAG and NAM are synthesised in the cytoplasm from glucose.

28
Q

What is the second step in PG synthesis?

A

Transport into the periplasm, assembled into a PG chain by glycosyltransferases, transpeptidases and carboxypeptidases

29
Q

What are the functions of the three PG enzymes in the periplasm?

A

GT adds precursors to growing PG chain
TP crosslinks through peptide bond formation
CP remove D-alanine to facilitate cross linkage.

30
Q

What is the function of bactoprenol?

A

Covalent attachment of the finished cross-linked molecule to the cell membrane.

31
Q

How can PG wall influence shape of the cell?

A

3D mesh like structure of repeating sugars and short peptide chains.

32
Q

What are examples of PG cell wall determining shape?

A

Helical arragnement forms cylindircal rod-shaped bacteria.

33
Q

Penicillin Binding Proteins

A

These are membrane associated proteins involved in the biosynthesis of PG.

Biology - Microbiology (19 decks)

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