Midterm 1 Flashcards
Main difference between bacteria and archea
Bacteria have peptidoglycan in cell wall
Strain
Descendants of a single pure culture
Species
Group of strains with similar traits
What does a simple stain show
Size, shape, morphology
Hyperthermophiles
High temperature, branched saturated membrane
Psychrophiles
Low temperature, unsaturated membrane, fewer H bonds
Acidophiles
Low pH, pump H+ out of cell
Alkaliphiles
High pH, increase H+ in cell, produce acidic metabolites
Comensals
One benefits, other is unharmed
Differential media
Distinguish what bacteria possess certain traits by interaction with media
MacConkey Agar selects for…
Gram Negative Cells
MacConkey Agar differentiates….
Lac+ from Lac-
Binary Fission
Primary reproduction of bacteria
2 daughter cells from mother
Steps of binary fission
- DNA replication
- Elongation
- Septum forms via divisome
- Cells split
4 growth phases of bacteria
- Lag
- Log
- Stationary
- Death
Lag phase
Nutrients/DNA being replicated, cells not splitting yet
Log phase
Cells rapidly split and number increases exponentially
Stationary phase
Nutrients are low so growth slows
Cell density high
Death phase
Cells degrade
Months to years
Counting chamber
Manually counts cells/mL from a plate
Live and Dead cells
Plate counting
Manually count colonies from a plate
CFU (collony forming unit)
Only shows viable cells
Limitations to plate counting
Colonies can blend together
1 colony can come from multiple cells
One cell can only make one colony
Serial dilutions
Make plate counting easier to count/more accurate
Cell mass methods
- Dry weight
- Turbidity
Dry weight mass
Will include live and dead cells
Turbidity
Uses spectroscopy
Based on absorbance/scattered light
Includes dead cells
Hypertonic solution
Water leaves cell
Hypotonic solution
Water enters cell
Compatible solutes
For hypertonic solutions
- Prevents escape of water from cell
How does a cell react to a hypotonic solution
Mechanosensitive channels
- Water enters cell
- Cytoplasm stretches
- Channels open
- Solutes leave cell
Osmotic pressure relieved
Damage caused by pH changes
Cytoplasmic membrane, protein activity
How is cytoplasm pH maintained
Importing or exporting protons
What group exports protons
Acidophiles
Inside pH is too low (acidic)
Therefore, make more basic
What group imports protons
Alkalphiles
Inside pH too high (basic) therefore, make more acidic
What do hyperthermophiles have that others don’t
Most ether lipids
Levels of temperature bacterium
Psychrophiles
Psychrotrophs
Mesophiles
Thermophiles
Hyperthermophiles
What temperature does mesophiles like
Human body temperature
~37C
What are most psychrophiles responsible for
Refrigerated food spoilage
What are most mesophiles responsible for
Human pathogens
What role does oxygen have with bacteria
Essential for some, toxic to others
How does oxygen damage some bacteria
Forms Reactive Oxygen Species (ROS)
Oxidizes sensitive groups
Reactive Oxygen Species do what
React with proteins lipids, nucleic acid
Remembering why oxygen can be toxic
H2O vs H2O2
How do bacterial enzymes help protect against ROSs
Break down molecule/change it
2H2O2 -> 2H2O + O2
Obligate aerobes
Need oxygen
Obligate anaerobes
Grow without oxygen
What does oxygen kill
Obligate anaerobes
What does oxygen do to facultative anaerobes
Beneficial, not essential
What does oxygen do to aerotolerant anaerobes
No impact
What levels of oxygen do microaerophiles need
Low Oxygen
Can’t survive atmospheric levels
Testing Oxygen sensitivity
Top is oxic
Bottom is anoxic
Wherever cells end up in tube show ideal oxygen levels
Autoclaving
High pressure steam
Sterilizes
Pasturization
Kills pathogens with moderate heat
What does cold do to bacteria
slows metabolic activity
What effect do hypertonic conditions have on microbial growth
Dehydration slows microbial growth
What do extreme pH conditions do to microbial growth
Impacts protein function and slows growth
What products have general targets
Disinfectants and antisepctics
Disinfectant
Used for objects
Antiseptic
Used on live tissue
What have specific targets
Antibiotics
Targets are specific to bacteria
Oligotrophic environment
Low nutrients
Bacteria activate stringent response
Response to oligotrophic environment
Slowed metabolism, increased protein production to protect cell/dna
Persister cells and endospores can form
Persister cells
Growth arrested bacterial cells
Resistant to antibiotics
Endospores
Form inside a vegetative mother cell
Different structure, same genetics
Released via lysis
Resistance of endospores
Highly resistant to UV, heat, desiccation
Protected against chemicals, antibiotics, phage
Advantage of endospores resistance
Better survival in poor conditions
Can reform vegetative cells in proper conditions
What does the core of an endospores contain
Nucleotide
Ribosomes
Etc
What surrounds an endospore core
Cortex (peptidoglycan)
Coat (Protein)
Exosporium
Impermeable
Endospore formation
- Cell division
- Septum forms
- Forespore develops
- Forespore engulfed
- Cortex forms
- Coat forms
- Lysis
Planktonic
Free floating (bacterium in lab)
Biofilm
Communities of bacterium forming a matrix (in nature)
Formation of biofilms
- Quorum sensing
- Autoinducer secreted (proportion relative to amount of cells)
- High AI = pili made
- Extra cellular polymeric substance (EPS) made
Planktonic to Biolfilm
- Adhesion to surface -> sessile
- Cell division
- Cells stick and make EPs
Bacterial adhesion to host cells is
Specific via adhesions
Bacterial adhesion to abiotic surfaces is
Non-specific via bacterial components
What is the EPS
Slimy matrix, helps attach bacteria
Traps nutrients
Secreted or released via death
What kind of gradient formed by biolfilms
Oxygen gradient
Explain oxygen gradient of biolfilms
Surface = more oxygen = more nutrients = more metabolically active
Innate immune response
Nonspecific but fast
Adaptive immune response
Specific but slow
Chemical mediators
Promote inflammation, opsonization, make pores in cell wall
Opsonization
Help phagocytes recognize bacteria
Opsonization process
- C3b binds surface
- Receptors on phagocyte recognize c3b
- Phagocytoses
Dendritic cells
Degrade antigens, activate T and B cells
Infection stages
- Adhesion
- Proliferation
- Invasion
- Tissue damage
Active penetration
Virulence factors
Passive penetration
Unrelated event (broken skin)
How do pathogens avoid detection
Intracellular pathogens
How do pathogens avoid recognition
Modify, decrease, hide antigens
Endotoxin
Lipopolysachharide (LPS)
Released if cell is listed
Can lead to sepsis
Exotoxins
Secreted
Ex. Neurotoxins
Quinolones/fluoroquinolones
Target topoisomerase of bacterium
narrow host range
Closely related species can replicate plasmid
Broad host range
Plasmid can be replicated in many species
How are plasmids classified
Accessory genes
Resistance plasmids
Protect bacteria against antibiotics
Virulence plasmids
Genes for virulence factors
Example of virulence plasmids
Enterotoxigenic E.Coli (ETEC)
What does ETEC plasmid encode for
Pili and toxins
Conjugation plasmids contain what
Sex pilis genes, MOB genes
What do MOB genes do
Encode proteins
Deliver plasmid into pilus
Mobilizable plasmids
MOB genes, no sex pilus genes, needs pilus from other cells
Transposable elements
Nucleic acid that can be transferred between DNA molecules (transposition)
Within chromosome
Chromosome to plasmid
Simple transposition uses what mechanisms
Cut and paste
replication transposition uses what mechanisms
Copy and paste
Transposable elements
Insertion sequence
Inverted repeat
Insertion sequence does what
Encodes transposase
Has inverted repeats on either end
What do inverted repeats do
Recognition sites for transposase
What does transposase do
Cuts DNA at IRs for transposition and inserts
What are direct repeats
Repaired dna flanking IRs after transposition
Unit transposons have what
IRS
Transposase gene
Resolvase gene (or others)
Accessory genes
Significance of transposons
Prevent inactivation of genes in new chromosome, transfer accessory genes
What do conjugation genomic islands encode
Excision, conjugation, integration
What do mobilizable genomic islands encode
Excision, integration
Pathogenicity islands do what
Carry virulence factors
Turn a safe cell into a pathogen
What must new DNA do to be retained
Integrate into genome
OR
Replicate apart from genome
Example of conjugation
F factor
Steps of Conjugation: F factor
- Donor cell expresses sex pilus
- Attaches sex pilus to recipient cell
- Protein changes in pilus convert it to a type 4 secretion system (T4SS) - retracts
- Relaxosome cuts at oriT site - replication
- MOB genes encode coupling factor - pulls dna to T4SS
- DNA enters recipient
- Replication
What is transferred when making an Hfr cell
Bacterial chromosome and F factor
Recombines
What is transferred from an Hfr cell
Bacterial chromosome and F factor
Makes F’
Transformation requires what
COM proteins
what can trigger competence
Cell signalling
Nutritional stress
DNA damaging agents
Process of transformation
- Secrete competence-stimulating peptide (CSP)
- Threshold met = receptor activated
- Com genes transcribed
Why is there a threshold for CSP
Makes sure there are other cells present for exchange
Com proteins
Transformation pilus
Membrane receptor
Nuclease
Transport Complex
Transformation pilus
Binds dsDNA
Membrane receptor
Binds dsDNA at other end and attaches it to cell surface
Nuclease
Cuts dsDNA to make ssDNA
Transport complex
Sends ssDNA into cytoplasm
What does RecA do - lac operon
Catalyzes recombination of ssDNA
Artificial competence
Lab induced competent bacteria
2 methods of artificial competence
- Chemical (calcium chloride and heat shock)
- Electroshock
What is the name of a phage that mediates transfer
Transducing particle
Lyric cycle - phage
- Absorbtion
- Injection
- Degradation of host dna
- Protein synthesis and packaging
- Lysis
Generalized transduction
Randomly incorporating pieces of host dna into phage during lytic cycle instead of lytic dna
Forms transducing particle
What can a generalized transducing particle do
Inject dna, no lytic cycle
Lysogenic cycle - phage
- Absorbtion
- Injection
- Integration
- Replication of cells
- Trigger causes lytic cycle to begin
Specialized transduction
Contains bacterial dna from beside excision site of phage dna
Lysogenic conversion
Conversion of Lysogenic phenotype via prophage
Prophage
phage dna
Extracellular vesicles
Contains cargo
Gram negatives
Steps of pathogensis
- Sense host environment
- Make needed proteins for attachment
- Evaded immune system
- Kill host cells
Sigma factors
Guide RNAP to promoter
Closed complex - transcription - occurs when
RNAP holoenzyme binds to promoter
Open complex - transcription - occurs when
RNAP unwinds DNA
2 types of terminators
Factor dependent (Rho)
Intrinsic (Hairpin)
Constitutive genes
Essential genes, always needed
Negative transcription control uses what
Repressors
Riboswitch - transcription
Leader region - 2 conformations
Allows or prevents transcription to continue
Requires metabolite or ligand
Process of a transcription riboswitch that is usually off
Metabolite forms anti terminator
Transcription continues
Process of a transcription riboswitch that is usually on
Metabolite forms anti-antiterminator
Termination stops
What is essential for bacterial replication
Ribosomes - translation
What do many antibiotics target
Ribosomes
Initiator tRNA
First tRNA needed
Charged with fMET in bacteria
Anticodon binds to start codon
What is responsible for charging tRNA correctly
Aminoacyl-tRNA synthetases
What bond binds amino acid with tRNA
Reactive ester bond
What binds are formed between aminos in tRNAs
Peptide bonds
Initiation of translation
- 16s bind to RBS
- Initiator binds to start codon in P site
- Initiation factors help if needed
- Forms 30s Complex
- 50s joins 30 S
Elongation - translation
- EF-Tu delivers tRNA to A site
- Anticodon binds
- Peptide bond formed (PTC)
- Translocation (EF-G)
Termination - Translation
Stop codon - release factors
Tetracyclines
Bind to A site, block delivery
Bacteriostatic
Bacteriostatic
Inhibits growth, does not kill
Macrolides
Bind 50 S, block E site
Lincosamides
Binds 50S A site
Blocks peptide bond formation
2 conformations of riboswitch - translation
Sequester
Anti-sequester
Sequestor
Blocks RBS
Anti-sequestor
RBS available
Cis-encoded sRNA
Matches template strand
Trans-encoded sRNA
From other DNA
How does sRNA impact translation
Binding RBS: block initiation
Binding gene: block elongation
Binding Leader: prevent sequestor
Binding mRNA: degrade mRNA
RyhB sRNA
Fur: repressor
Fe2+: co-repressor
Limited Fe2+: what happens
RyhB binds mRNA of non essential proteins -> degradation -> more iron for needed protein
High Fe2+: what happens
Fe2+ binds to Fur, does not translate ryhB, no mRNA degraded
Proteolysis
Enzyme, transcription/translational factors
Cleave one part of synthesis, limits production of protein
Multilevel regulation example
RpoE: sigma factor
Binds to RNAP
Controls damage repair genes
RseA: anti-sigma factor
Prevents RpoE from binding RNAP
Regulates when damage repair genes are coded