Micro - E3 Flashcards
Clostridium difficile is a ____-shaped, _____-forming, Gram-______ bacterium
It is also a strict ______.
Clostridium difficile is a rod-shaped, spore-forming, Gram-positive bacterium.
It is also a strict anaerobe.
C. diff synthesizes two large toxic proteins. What is their function?
These two large toxin proteins (TcdA, TcdB) disrupt the intestinal epithelium
Name 5 microorganisms
Bacteria Viruses Yeast and Fungi Protozoa Archaea: commensals, but no known pathogens
What are the 4 key differences between prokaryotes and eukaryotes?
Nuclear membrane
- eukaryotes –> YES
- prokaryotes –> NO
Membrane-bound organelles - eukaryotes –> YES
- prokaryotes –> NO
Endocytosis
- eukaryotes –> YES
- prokaryotes –> NO
Volume
- eukaryotes –> 1 µm3
- prokaryotes –> 1000 µm3
Rod shaped bacteria –> “_____”
Sphere shaped bacteria –> “_____”
Rod shaped bacteria –> “bacilli”
Sphere shaped bacteria –> “cocci”
Describe gram positive bacterial envelopes
Thick peptidoglycan layer (bacterial cell wall)
Describe gram negative bacterial envelopes
Thinner peptidoglycan wall + lipopolysaccharides + endotoxin
The makeup of polysaccharide chains of peptidoglycan
Repeating disaccharide units –> -M-G-M-G-M-G-M-G-
M = N-acetylmuramic acid G = N-acetylglucosamine
Peptide side-chains are attached to _______________ of peptidoglycan, and are unique in that they contain _______________.
Peptide side-chains are attached to N-acetylmuramic acid of peptidoglycan, and are unique in that they contain amino acids in the D conformation.
What determines bacterial cell shape?
Pattern of cross-links between peptide side chains of peptidoglycan of cell wall
How does penicillin harm growing bacterial cells?
Penicillin mimics structure of D-Ala-D-Ala Chains –> prevents cross links from being formed on growing bacterial cells –> lysis
- does not do anything to pre-existing cross-links
How to prokaryotes undergo cell division?
Binary fission
*Much faster than mammalian cell growth in culture
Describe the bacterial growth curve
Growth is exponential –> during each doubling time the population increases by a factor of 2.
Except for very short periods, exponential growth does not occur in nature.
*growth rate depends on nutrient composition of medium.
Lag phase
Time it takes for a bacterial cell that has not been growing to…
- sense that it has entered a nutrient-rich environment
- use nutrients to repair any cellular damage, make the cellular compounds for unrestricted growth
Stationary phase
- Secretion of degradative enzymes
- Transport of secondary nutrients
- Intracellular catabolic pathways
- Motility and chemotaxis
- Genetic competence
- Antibiotic and toxin production
- spore formation
Prototrophs
Bacteria that have no requirements for organic compounds other than a simple carbon source (e.g., a sugar).
Auxotrophs
Bacteria that have more complex nutritional requirements, typically requiring amino acids and/or vitamins and/or pyrimidines and/or purines.
- C. difficile is a natural auxotroph
What are the two ways that bacteria may satisfy their energy needs?
- Fermentation: (“substrate-level phosphorylation”) synthesize ATP through enzymatic rxns of glycolysis
- Respiration: synthesize ATP through electron transport chain and ATP synthase
Difference between aerobic respiration and anaerobic respiration
Aerobic respiration: electron acceptor = oxygen; produces H2O
Anaerobic respiration: electron acceptor = fumarate, nitrate, other
Strict aerobes
- terminal e- acceptor for respiration –>_________
exp. _________________
Strict aerobes
- terminal e- acceptor for respiration –> oxygen
exp. Mycobacterium tuberculosis (lungs)
Strict anaerobes
- terminal e- acceptor for respiration –>_________
exp. _________________
Strict anaerobes
- terminal e- acceptor for respiration –> organic molecule
exp. Bacteroides, Clostridium (colon)
Facultative anaerobes
Can carry out aerobic respiration if oxygen is present, or anaerobic respiration or fermentation if no oxygen.
Exps.
- Escherichia coli (small intestine),
- Vibrio cholerae (small intestine)
- Streptococcus pneumoniae (nasopharynx, lungs),
- Pseudomonas aeruginosa (lungs)
Spores
- triggered via nutritional limitation
- hardy, non-growing structures
produced by some Gram-positive bacteria (Bacillus and
Clostridium) - low water content allows them to survive harsh conditions
Examples of spore-forming pathogens
Clostridium difficile –> pseudomembranous colitis
Clostridium botulinum –> botulism (flaccid paralysis)
Clostridium tetani –> tetanus (spastic paralysis)
Bacillus anthracis –> anthrax
Bacillus cereus –> food poisoning
Organization of Toxin Genes - Pathogenicity Locus (PaLoc)
Pathogenicity Locus (PaLoc) is composed of several transcription units. The genes (involved in production of toxins) are transcribed from multiple promoter sites.
Operon
In bacteria –> multiple functional related genes often organized into transcriptional units called operons.
Genes are typically co-transcribed from common promoter
Bacterial DNA-Dependent RNA polymerase
Template dependent –> needs a DNA primer
Have β, β’, α, and σ subunits
Inhibitors of RNA synthesis bind the __ subunit of RNAP.
Inhibitors of RNA synthesis bind the β subunit of RNAP.
Inhibitors of RNAP (bind __ subunit)
Rifamycins: Blocks ________
Example: ________
________: Blocks ______
Example: fidaxomicin
Inhibitors of RNAP (bind β subunit)
Rifamycins: Blocks elongation
Example: rifampicin
Lipiarmycins: Blocks initiation
Example: fidaxomicin
Role of σ subunit of bacterial DNA-Dependent RNAP
σ subunit
- causes stable binding at promoter regions
- reduces binding at non-promoter regions of DNA
- removal allows escape from the promoter (translocation) and elongation of the transcript
There is one type of RNAP core enzyme.
Many kinds of __ subunits (recognize promoters with different sequences)
One type of RNAP core enzyme.
Many kinds of σ subunits (recognize promoters with different sequences)
How does factor-Independent termination stop transcription?
A Factor-Independent termination site is encoded in the DNA sequence appearing as a region of dyad symmetry.
Results in an RNA sequence that is able to form a stem-loop structure.
How does factor-dependent termination stop transcription?
Rho (ρ) factor binds directly to RNAP and causes RNAP to stop and release when reaching the factor-dependent terminator.
Describe how transcription can be positively regulated
X
- positive regulator
- binds UPSTREAM of promoter
- has affinity for RNAP, stabilizes RNAP binding at the promoter and helps recruit promoter
Describe how transcription can be negatively regulated
Y
- negative regulator (repressor)
- can overlap promoter, or be downstream of promoter
- If active, gene not turned on
TcdR is a _______ factor for toxin gene expression.
During which phase it made?
Sigma factor. Recognizes the promoter sites for the tcdA and tcdB genes.
tcdR made during stationary phase
How is CodY a repressor?
CodY binds to the tcdR promoter region and prevents RNA polymerase from binding to the promoter.
Able to do this by sensing presence of amino acids like isoleucine (nutrient xs (more ile) –> active CodY)
TcdC
An anti-sigma factor.
Binds and inactivates TcdR. Deals with “leaky expression” of TcdR during exponential phase
Deficiency in TcdC
Results in more active TcdR –> could cause high toxin production because
Commensal relationship
microbe benefits, host unaffected
Which areas of the body have been shown to NOT be colonized?
CNS/Spinal Fluid
Blood