PGL synthesis+ Transport Flashcards
Peptidoglycan
Large polymer that forms a mesh-like scaffold around the bacterial cytoplasmic membrane
Cable-like structure
two principal components:
Glycan strands of repeating disaccharide units
Peptide chains of 2 to 5-amino acid residues
Peptidoglycan structure
Alternating repeats of Nam +Nag
NAM-N-acetylmuramic acid
NAG-N-acetylglucosamine
Amino Acids: L-alanine,D-alanine, D-glutamic acid, Diaminopimelic acid (DAP)
PGL Polymer
Strands of PGL form a sheet surrounding the cell
Connected by peptide cross-links-vertical
Dap forms cross-links with other peptide chains
B-1,4-glycosidic bonds
between Nag+Nam-horizontal
Variation
+cross links contain short peptide interbridge
- cross-links form DAP of one glycan strand to d-alanine on the adjacent strand
Synthesis
Important for cell elongation
three stages
Precursor formation: within cell, nag +Nam,occurs in the cytoplasm,polymerization:form functional PGL strand
Cross-linking
1st step
Autolysins break B-(1,4)-glycosidic bonds
cuts PGL strands-breaks bond
2nd step
NAG-undecaprenyl phosphate formed in cytoplasm
Activated monosaccharide-sugar with UDP
3rd step
NAM-pentapeptide-UDP formed in cytoplasm
also known as park’s nucleotide
4th step
Bactoprenol-P picks up P-NAM-5aa,becoming Lipid l
UDP adds NAG, forming Lipid ll,bactoprenol+ PGL monomer
5th step
Bactoprenol ferries PGL monomer across membrane, to periplasmic space, catalyzed by flippase
6th step
NAM-NAG subunit brought in by bactoprenol, which is recycled.
7th step
Glycosyltransferases form B-(1,4)- glycosidic bonds
8th step
Transpeptidases form peptide cross-links
Transport
In two groups
Passive: Move things with the gradient=diffusion
Active: Against the concentration gradient-Energy
Simple Diffusion
Passive movement of molecules or ions across a membrane
without a helper protein
Facilitated Diffusion
It is the same as simple diffusion but with transport protein in the membrane
Primary active transport
Requires energy-against gradient
most common is ATP
Very specific
specific transporters=specific molecules or ions
Simple transport
Membrane-spanning transport protein
Powered by proton motive force
transfer of H+ through proton pump
through ATP synthase drives ADP to ATP
Group translocation
power=Phosphor enol pyruvate
import sugars-Phosphorylates sugars as they come in
PEP to a sugar molecule
ATP-binding cassette transporter (ABC)
High substrate affinity
power= ATP
Variety of compounds-pump out antibiotics +toxins
Solute-binding protein: G+ out, G- periplasmic space.
Secondary active transport
Co-transport
The energy created by primary active transport to transport other molecules against their concentration gradients
Symport
Molecules move in the same direction
High to Low
uses energy from primary
Antiport
Molecules move in the opposite direction
one in, one out
