Bacterial Structure Flashcards
What is the structure of gram +tve cell wall?
Monoderm- thick outer peptodoglycan layer and inner cytoplasmic membrane
What is the structure of gram -tve cell wall?
Diderm- thin peptidoglycan layer, and outer and inner membrane either side
What feature is common to both -tve and +tve?
Inner cytoplasmic phospholipid bilayer membrane
Describe the structure of peptidoglycan in gram +tve bacteria
Thick Layered sheets of alternating modified glucose residues (glycan sheets)
Describe the structure of peptidoglycan layer for gram -tve bacteria
Thin Layered sheets of alternating modified glucose residues (glycan sheets)
What makes up the gram +tve and -tve glycan sheets?
Alternating NAG and NAM, connected by B-1,4 glycosidic bonds
What are the amino acid residues that come off NAM in gram negative (desceding order)?
L-Ala D-Glu DAP D-Ala
How are glucan sheets cross-linked in gram -tve peptidoglycan?
Direct peptide link between DAP on upper and D-Ala on lower
What are the amino acid residues that come off NAM in gram positive (desceding order)?
L-Ala D-Glu L-Lsy D-Ala
What is difference between residues off NAM in +tve and -tve?
DAP in -tve = L-Lys in +tve
How are glycan sheets crosslinked in gram +tve peptidoglycan?
L-Lys on upper attached to penta glycine interbridge attached to D-Ala on lower
What does gram +tve cell wall have that -tve doesn’t?
Techoic acid, which protrudes from peptidoglycan- involved in changing antigenic properties
What are key features of gram -tve outer membrane?
Contains many lipopolysaccharides (LPS) Also has outer membrane proteins
What is the general structure of LPS, wrt variability?
O-antigen polysaccharide - core polysaccharide - lipid A
Highly variable Highly conserved
Where is lipid A found in the membrane?
Lipid A is the raft that embeds into the membrane
What is the role of the O-antigen polysaccharide region?
It is highly variable, and is very important in antigenic variation
What is the role of lipid A?
It is a highly toxic endotoxin, can induce severe and rapid illness
What is the typical structure of transmembrane outer membrane proteins?
A B-barrel structure, with a central membrane spanning channel. Surface-exposed loops of variable lengths
What are outer membrane proteins important for?
Initial binding/anchoring to host cells
What is the structure porin proteins?
Consist of 3 transmembrane protein subunits. Forms small water-filled channels through the membrane, allows diffusion of small hydrophilic molecules
What is OmpA and what it’s role?
One of the most abundant outer membrane proteins. Important role in maintaining structural integrity of outer membrane. Also involved in adherence
What are capsules?
Composed of polysaccharides and sometimes proteins, capsules form on the outside of bacteria as a coat.
Thick, amorphous structure
Contribute towards immune evasion and biofilm formation
What is the variability of capsules?
Composition varies between different bacterial species, and among strains of the same species. Capsule diversity is responsible for serotyping schemes (e.g. E coli K1, K2)
What is the S-layer?
Generally made up of proteins or glycoproteins that self assemble into an ordered crystalline lattice at the cell surface- anchored to cell envelope.
Important in aggregation and biolfilm formation
Resistance to immune response and adverse environmental conditions
Can be used in adhesion
