Exam 1: Lectures 1-7 Flashcards
Regulators for stationary phase gene expression
- sigma s
- cAMP-CRP complex (increase expression of genes, like ones that code for enzymes that can supply energy independent of glucose)
- Guanosine tetraphosphate, or alarmone (inhibits rRNA, ribosomal protein, and tRNA synthesis during amino acid starvation (stringent response), this also leads to decrease in other protein production
Role of D-alanine substitutions in innate immunity
D-ala substitutions add positive charges to LTA, increasing positive charge of cell wall
- Positive cell wall repels cationic antimicrobial peptides (CAMPs), such as polymyxin, beta-defensins
D-ala substitutions play an important role in immune recognition and cytokine production
- Toll-like receptor 2 is involved
Limitations of measuring growth via viable cell counts
(serial dilutions and determining colony-forming unit by plating)
will give an underestimation if cells are clumped or in chains because each clump or chain will give rise to a single colony
Function of peptidoglycan in mycobacterial cell wall
Provides rigidity
MIC, MBC
minimum inhibitory concentration
minimum bacteriocidal concentration
(relating to antibiotics)
LPS biosynthesis
Three parts created individually
Core oligosaccharide added to lipid A, then O-antigen added to lipid A-core oligosaccharide molecule by a ligase, then completed LPS molecule is translocated across periplasm and outer membrane by LPS transport proteins (Lpt A, B, C, etc.)
Function of surface proteins in mycobacterial cell wall
Variety of activities, e.g. act as enzymes and adhesins
Events before septum formation in bacterial cell division
- DNA synthesis initated when cell reaches critical mass
- Two copies of chromosomes are formed
- Chromosome partition occurs (sister chromosomes move to opposite cell poles)
- Replication origin anchored to cell poles, remaining chromosomes continue to migrate to daughter cells
BCG vaccine
live, attenuated bovine strain of tubercule bacillus (M. bovis)
Uncertain efficacy, not routinely used in US (low incidence, prevents use of tuberculin test to determine spread)
Phospholipid
Two fatty acid chains attached to 2 carbon atoms of glycerol by ester bonds, a phosphate attached to third carbon atom of glycerol
- small organic groups linked to phosphate group give variety
Amphipathic - fatty acid chains hydrophobic, head hydrophilic - form micelles when placed in aqueous environment
PBP3
Penicillin binding protein specifically important for peptidoglycan synthesis in the septum
Type 4 pili assembly
Major pilin (PilA) and minor pilin are proccessed by the inner membrane peptidase PilD
Processed pilins accumulate in inner membrane, where they are polymerized into a helical fiber by hexameric ATPase PilB (extension)
Depolymerization of pilins by the ATPases PilT and PilU results in pilus retraction
Polymerizeed fiber extends to the exterior via the secretion pore formed in the outer membrane by PilQ, and (hypothesized) with the help of actin-like PilM and inner membrane proteins PilN, PilO, and FimV, which form a complex with PilP, PilF, and PilQ
Pseudopeptidoglycan
Glycans:
- a beta-1,3 glycosidic linked NAG and N-acetyl-talosaminouronic acid (NAT)
- lysozyme cannot digest beta-1,3 glycosidic bonds
Peptides:
- only L-amino acids
- attached to NAT
- cross-linked directly between the lysine and glutamate residues
- penicillin is ineffective in inhibiting the cross-linking
Septum formation in bacterial cell division
- MinE forms a membrane-associated ring at cell centre, relieving inhibition of FtsZ ring formation by MinCD
- FtsZ recruited to cell centre and begins forming FtsZ ring (probably with help from ZipA)
- Other proteins (FtsA, FtsW) recruited to the ring to form the septal ring
- Further recruitment of other proteins (FtsK, FtsI, FtsN) and the septal ring constricts and MinE ring disassembles
- Constriction is completed, MinE forms a new ring at the centers of the daughter cells
Peptidoglycan biosynthesis (steps)
- UDP derivatives of amino sugars are made in the cytosol
- Amino sugars are transferred to a lipid carrier in the membrane, which carries them across the membrane
- The peptidoglycan is polymerized on the outer surface of the membrane
- A transpeptidation reaction cross-links the peptidoglycan with other peptidoglycan molecules
Phospholipid biosynthesis
ACP-fatty acid chains added on to glycerol-3-phosphate, forming phosphatidic acid
Phosphatidic acid is then coupled to CTP, releasing PPi and forming CDP-diglyceride
- Cytidine diphosphate (CDP) is used as a carrier
Head groups are added to CDP-diglyceride
- serine added, forming phosphatidylethanolamine (PE)
- G3P added, forming phosphatidylglycerol (PG)
Major porins in E. coli
OmpC, OmpF, PhoE
OmpC = smaller and more abundant than OmpF in high osmolarity media and in the intestine
PhoE is produced only under phosphate-limiting conditions to facilitate phosphate uptake
Twitching
Form of cell motility expressed as a jerky translocation over a solid surface
Results from constant extension and retraction of type 4 pili
Catalase
Enzyme produced by aerobes and facultative anaerobes to eliminate hydrogen peroxide by converting it into water and oxygen
Periplasmic space
The space between the outer and cytoplasmic membranes, has an oxidizing environment that allows disulfide bond formation (bacterial cytoplasm is a reducing environment)
Cytoplasmic steps of peptidoglycan synthesis
- NAG-1-phosphate attacks UTP, displacing pyrophosphate and forming UDP-NAG
- Some of the UDP-NAM is converted to UDP-NAM
i) PEP adds enolpyruvate to UDP-NAM, creating Pi and UDP-NAG-enolpyruvate
ii) NADPH reduces the enol derivative to the lactyl moiety (UDP-NAM)
3) sequential addition of L-ala, D-glutamate, L-R3, D-ala-D-ala, and 4ATP to create UDP-NAM-pentapeptide (aka Park’s nucleotide)
4) Parks nucleotide added to membrane lipid carrier
Autolysins
Cell wall hydrolases produced by the bacteria for breakdown of cell wall during cell division/separation, wall morphogenesis and turnover, biofilm formation, and DNA release
N-acetylglucosaminidase and N-acetylmuramidase cut the glycan backbone (which is made of NAG and NAM)
Endopeptidases cut the peptide
Bacitracin
Antibiotic that acts on the bacterial cell wall
Blocks release of Pi from lipid carrier (undecaprenyl-PP —> undecaprenyl-P + Pi), blocking the lipid carrier recycling
Toxic, so only used topically (eg polysporin ointment)
S. aureus
Gram positive bacterium