EXAM Lecture 10 Flashcards
Eukaryotes vs Prokaryotes
Eukaryotes:
- cell size is 10-100 um
- cell division through mitosis and mieosis
- no cell wall
-70s ribosomes
- membrane bound organelles
Prokaryotes:
- cell size is 1-10 um
- cell division through asexual reproduction by binary fission
- cell wall:
* gram positive: PGN
*gram negative: LPS (& PGN sometimes)
- 80s ribosomes
- no organelles
Types of bacterial cell wall
GRAM NEGATIVE
- LPS (some PGN?)
GRAM POSITIVE
- PGN
PGN: Peptidoglycan (GRAM +)
Bacterial cell wall consists of peptidoglycan; a polymer consisting of NAG and NAM (alternating) and short chains of amino acids (bind everything)
in the final stages of peptidoglycan synthesis, there are cross linking reactions that involve pennicilin binding proteins (PBPs)
- these PBPs were named after the discovery that penicillin binds to these proteins, which disrupts the cross linking reactions and disrupts peptidoglycan synthesis
Penicillin interferes with peptidoglycan synthesis
- inhibition of PBPs leads to irregularities in cell wall structure and cell death - this is the mechanism of action of penicillin
Peptidoglycan structure
answering how the PGNs come together:
legend:
- NAM
- NAG
- side chain amino acid (binding layers vertically/above)
- cross bridge amino acid (overall binding)
alternating NAM and NAG molecules form a carbohydrate backbone (glycan portion)
rows of NAG and NAM are linked by polypeptides (peptido portion)
the structure of the polypeptide cross bridges may vary but they always have a tetrapeptide side chain, which consists of 4 amino acids attached to NAMS (important component for signaling the host)
the Gram positive bacteria cell wall
consists of many layers of peptidoglycan and also contain teichoic acids
- lipid and/or cell wall associated:
* wall teichoic acids
*lipoteichoic acids (bind to plasma membrane)
techoic acids function to:
- bind and regulate movement of cations into and out of cell
- structure: prevent extensive cell wall breakdown and possible cell lysis during cell growth (help hold everything together)
Gram + vs - PGN
gram negative:
- thin PGN layer
- gram negative DAP-type peptidoglycan
- four chains; third is MESO-DAP (rest same as +)
gram positive:
- thick PGN layer
- gram positive Lys-type peptidoglycan
- four chains; third is L-lysine
- (has tetrapeptide chains)
intestinal eptithelial cells and immune cells express surface receptors NOD1 and NOD2
- want to break chains up into fragments that can bind to host these host receptors
- example of microbial host signaling
- immune cells will then respond to these receptors because they want to know if they’re coming into contact with PGN
PGN gram negative chain
diagram
lytic transglycosylase: enzyme that breaks down cell wall into fragments
- breaks bonds between NAM and NAG
- AMIDASE: breaks NAM and tetrapeptide chain
- ENDOPEPTIDASE: breaks bonds between each AA
the three possible fragments after breaking down PGN that will bind to NOD1:
1. M-Tetra-DAP
2. M-Tri-DAP
3. iE-DAP
these are ligands for the NOD1 receptor
*ALL peptidoglycan fragments are ligands for NOD1 receptor
- any peptidoglycan treatments that bind to NOD1 have to come from gram negative bacteria
PGN gram postive chain
still lytic transglycosylase (NAM and NAG) and endopeptidase (AAs) being used to break bonds
only one possible fragment that PGN breaks down into:
- MDP (muramyl dipeptide)
MDP is the ligand for the NOD2 receptor
*any peptidoglycan fragments that bind to NOD2 have to come from gram positive bacteria
NOD signaling
diagram
The NOD1 and NOD2 receptors are located on the plasma membrane of many mammalian cell types
specifically, peptidoglycan fragments will bind to the NOD receptors;
- iE-DAP, M-Tri-DAP and M-Tetra-DAP bind to NOD1 receptors
- MDP binds to NOD2 receptors
NOD1 signalling ultimately activates transcription factor NFkB (in nucleus?)
NOD2 signalling ultimately activates NFkB and another transcription factor AP-1 (in nucleus) which promote host inflammatory responses (cytokines, inflammatory mediator enzymes)
