Review Slides I- 10/16/21 Flashcards
Difference between prokaryotes and Eukaryotes (4)
Prokaryotes
- No nuclear membrane
- No membrane bound organelles
- No endocytosis (have cell wall)
- Much smaller
Bacillus
Rod shaped
Cocci
Round
Gram positive color
Purple
Gram negative color
Pink
Gram positive cell wall structure
Thick peptidoglycan covering with lipoteichoic acid
Gram negative bacteria cell wall
Thin peptidoglycan layer with asymmetric outer membrane with lipopolysaccharide, less permeable
Example of endotoxin
Lipopolysaccharide, also superantigen
Transpeptidase
Enzyme responsible for linking D-Ala and L-Lys during peptidoglycan cross linking
Penicillin structure
Mimics D-Ala D-ala
Penicillin mechanism of action
Inhibits transpeptidase during bacterial growth, causes cell lysis
Bacterial growth curve stages (4)
- Lag
- Exponential
- Stationary
- Death
What happens in Exponential stage (4)
- Growth
- Synthesis of precursors
- Polymerize macromolecules
- Produce ATP, reducing power
What happens in stationary stage (7)
- Motility/Chemotaxis
- Secretion of degradative enzymes
- Transport of secondary nutrients
- Intracellular catabolic pathways
- Genetic competence
- Sporulation
- Antibiotic and toxin production
Two forms of RNA pol
Holoenzyme and core enzyme
Holoenzyme
Binds at the promotor, includes a2,B, B’, sigma
Core enzyme
Doing the transcription, Includes a2, B, B’
Transcription initiation
Sigma subunit leaves, core enzyme continues on
Where positive regulators bind
Upstream of promotor, aids RNA poly in binding to the DNA/transcribing
Repressor mechanism
Binds to the promotor, blocks RNA poly from binding
Promotor
Where RNA pol binds, -10 to -35 region
Pathogenicity Locus (PaLoc)
Organization of toxin genes and their regulatory elements, Tcd locus in C. Diff
Inactive CodY
In the absence of nutrients (isoleucine), it is inactive and can’t bind to the promotor region of tcdR to inhibit its transcription
Genes of the tcd PaLoc
TcdR (sigma factor), tcdB (Toxin), tcdE (holin), tcdA (toxin), tcdC (sigma factor)
TcdR
Sigma factor for the whole PaLoc, increases transcription
TcdB
Toxin
TcdE
Holin, allows the toxin to escape bacteria
TcdA
Toxin
TcdC
Anti sigma factor, in the presence of nutrients, it binds any existing tcdR protein and inhibits transcription
Active CodY
Active when bound to Isoleucine (nutrient rich environment) binds to the promotor of tcdR and inhibits transcription
Toxin
A protein that damages eukaryotic cells
Exotoxins
Most classical toxins
Organization of C. Difficile toxin
C terminal receptor binding carb region, middle hydrophobic region, cysteine protease domain (self cleavage), N terminal enzymatically active domain
How C. difficile toxin gets into the cell
Taken into early endosome after carb recognition, acid environment causes structural change which threads through endosome, self cleavage
Mechanism of enzymatically active domain of C. Diff
UDP-glycosylation of those proteins (G proteins)
Clostridium botulinum
Causes botulism, obligate anaerobic, gram-positive spore forming bacillus
Botulism hallmarks
Flaccid paralysis, intoxication (only take in toxin), rare, antibodies against toxin can alleviate symptoms
A-B toxin
B subunit recognizes the target cell and triggers RME, mediates membrane insertion
A subunit is enzymatically active, translocated by the B subunit
Botulism mechanism of action
A protease that prevents acetylcholine release in the peripheral nervous system, cleaves proteins involved in synaptic vesicles fusion, results in flaccid paralysis
Clostridium tetani
Causes tetanus, spore forming gram positive obligate anaerobe
Tetanus hallmarks
Spores of C. Tetani in soil can enter wound, germinate, and produce toxin
- Trismus and spastic paralysis
Tetanus toxin mechanism of action
A-B toxin that targets the CNS, prevents the release of inhibitory neurotransmitters (GABA) that causes spastic paralysis
Protein target of both tetanus and botulism
Synaptobrevin
Targets of only botulism
SNAP-25 and syntaxin
Cholera hallmarks
Vibrio cholarae, gram negative, comma-shaped, facultative anaerobe
Noninvasive, all symptoms are due to a single exotoxin, cholera toxin
Cholera toxin properties
A1-B5 stoichimetry (A is sitting in a donut hole)
Cholera toxin mechanism of action
ADP ribosylates the G protein critical to fluid balance, locking it “on”, increases secretion of Cl-, decreases Na+ absorption, leads to mass water secretion
Colonized sites (6)
- Nares
- Oral cavity
- Skin
- Small intestine
- Proximal colon
- distal colon
Maybe colonized sites
Stomach
Not colonized sites
CNS/spinal fluid
Blood
Why do we doubt studies with new sites?
- Could be experimental contamination
- Could be dead/killed bacteria
How many genes do we carry?
Human- 22,000
bacteria- 3,300,000
Over 99% bacteria
(Same amount of cells)
Functions of our symbiotic gut microbiome (3)
- Metabolic
- Immune and structural
- Protective
Metabolic functions of microbiome
- Synthesize vitamins (vitamin K)
- Harvest maximum energy through digestion (fermentation of complex polysaccharides)
- Controls epithelial differentiation and proliferation
Immune and structural functions of microbiome (4)
- Immuno system development and modulation
- Induction of IgA antibodies
- Enhancement of intestinal tight junctions
- Prevention of intestinal barrier dysfunction
Protective functions of gut microbiome (3)
- Competition for niche
- Competition for nutrients
- Production of antimicrobial factors
Factors that promote symbiosis (4)
- Exercise
- healthy diet
- Exposure to diverse microbes
- breast fed
Factors that promote dysbiosis (5)
- Formula fed
- Over sanitized environment
- Poor diet
- sedentary lifestyle
- Antibiotics
Point at which microbiome is fixed
~3 years (1000 days)
After that, you can only change the proportions or destroy with abx, can’t introduce new species
FGerm free mouse study on obesity
From discordant (one obese one thin) man twins, germ free mice receive gut microbiome, mouse that received thin twin stayed thin, mouse that got fat twin microbiome got fat, all things else the same
