Lectures 11, 12, 13 Flashcards
(32 cards)
What does bactericidal, bacteriolytic, and bacteriostatic mean?
Bactericidal- kills bacteria
Bacteriolytic- lysis/bursting of bacteria
Bacteriostatic- prevents growth/division
Therapeutic index- dose that kills humans over the dose that kills bacteria, less than 1 means the dose will kill human faster than bacteria
Slide 4 L11
How is does the closet an organism is to humans affect its ability to be distinguished?
Closer an organism is to humans, the harder it is to distinguish because it’s harder to damage the bacteria without damaging humans
Slide 6 L11
What are the 5 microbial targets?
- Inhibition of cell wall synthesis- penicillins, cephalosporins, bacitracin, vancomycin (inhibit peptidoglycan production or anything that damages cell well)
- Inhibition of protein synthesis- chloramphenicol, erythromycin, tetracyclines, streptomycin
- Inhibition of nuclei acid replication and transcription- quinolones, rifampin (could inhibit DNA replication since it’s circular in bacteria and linear in humans)
- Injury to plasma membrane- polymyxin B
- Inhibition of synthesis of essential metabolites- sulfanilamide, trimethoprin
What are cell wall inhibitors?
Natural and semi synthetic forms (more resistant to acid breakdown, more stable, broaden activity spectrum)
All contain β-lactam ring
Natural penicillin only works on gram +
Bacteriolytic
Slide 8 L11
What are protein synthesis inhibitors?
What are the 4 common drugs?
Many different classes interfere with ribosome/mRNA/tRNA complex
Chloramphenicol- can cause anemia, broad spec
Streptomycin- gram -, can cause deaf, targets mitochondrial ribosomes
Neomycin- topical streptomycin variant
Tetracycline- yeast over proliferation discolours developing teeth
What are the 2 plasma membrane damaging antibiotics?
Polymyxins- damage gram - membranes
Poorly absorbed and toxic to neurons and kidneys
Daptomycin- depolarizes gram + membranes
What are 2 nucleic acid synthesis inhibitors?
Rifamycin/rifampin- most useful against mycobacteria (TB, leprosy)
Inhibits mRNA synthesis
Highly permeable into cells and through cell walls
Quinilones- inhibit DNA gyrase->DNA replication
Slide 11 L11
What are metabolic inhibitors?
Sulfonamides (sulfadrugs)
Completely synthetic (originally used in dye making)
WWII soldiers got sulfa packets to spread on wounds to prevent gangrene
Completely inhibits an enzyme needed to generate folate (folic acid)
Folic acid is used to produce thymine and uracil
Slide 12-13 L11
What is sensitivity testing? (Disk diffusion and e tests)
Disk diffusion assays can determine what drugs are useful against bacteria (non quantitative, distance ranges for sensitivity and resistance)
Epsilometer tests (E tests) use a strip of antibiotic to determine a therapeutic dose MIC= minimal inhibitory concentration
How does antibiotic resistance work?
Even with proper use, bacteria will eventually become resistant to any antibiotic
Misuse of antibiotic accelerates the development of resistance (discontinuing the antibiotic before the pathogen is eradicated, using poorly choosed antibiotic, use of antibiotics against viral infections, preventative use of antibiotics in animal feed)
Resistance can also be natural in some bacteria and can spread to other bacteria
Slide 7 L11
What are the 5 modes of resistance in antibiotics?
- Drug modification/destruction- some can create enzymes to break down antibiotic (β-lactamases)
- Pathway protection- synthesis of false targets for tetracycline
- Target alteration- single mutation in a ribosome to prevent binding
- Rapid efflux- actively pumping out the antibiotic (heavy metal pumps)
- Alternative pathways- folate scavenging against sulfa drugs
What is synergistic inhibition in antibody resistance?
Using a combination of drugs to greatly decrease the chance of developing drug resistance
Combinations of antibodies result in both being more effective than one
Slide 10 L11
What is the basic structure of proteins? (Hydrophobic and hydrophilic)
Charge of R group is pH dependant
Hydrophobic- non polar R groups fold internally
Hydrophilic- polar R groups fold externally
What is an enzyme?
A protein (or RNA) that acts as a catalyst for a chemical reaction Makes reaction more favourable (more fast or more possible)
Needs right shape to hold the substrate and a catalytic center to facilitate the reaction (enzyme specificity)
How do we measure reaction rate and velocity?
Reaction rate (v) is how fast substrate is converted to product or how fast product is accumulated
V= -Δ[S] / Δt
V= +Δ[P] / Δt
Units are concentration over time (μM/s from μmol/L/s or mg/mL/s)
Slide 20 L11
What is initial velocity of an enzyme reaction?
Quickly measured for short period of time
Want it to be as fast as possible so reactions fast
Want optimum temperature and pH as well (have to find these at different times)
What are the two things rate is limited by?
Rate can be limited by the availability of the substrate
E + S -> ES
Rate can be limited by the production of the product
ES -> EP -> E + P
Slide 21 L11
What is the limiting step under optimal conditions with an excess of substrate?
The limiting step is how fast the enzyme can catalyze ES->E + P
Slide 22 L11
What is the Michaelis-Menten equation?
Vo = [S] Vmax / [S] + Km
Km= [S] at a Vo of 1/2 Vmax
Lower Km, more effective
Slide 3-5 L12
What is ALDH1 and ALDH2?
ALDH1 is found in the cytoplasm and has a high Km 0.1 mM
ALDH2 is found in the mitochondria and has a low Km 0.01 mM
ALDH2 if more efficient since we want a lower Km to work at
Mutations can cause ALDH2 to be slow to ALDH1 would kick in
What are the 5 steps to enzymatic studies?
- Come up with an assay that can be quantified
- Determine optimal conditions by plotting product accumulation vs time (determine fastest Vo)
- Determine the enzyme rate as we increase [S]
- Determine the Michaelis constant (Km)
[S] when Vo=1/2Vmax - Determine turnover number
-Kcat = Vmax/[E]t
Slide 9 L12
What is the lineweaver burk plot used for the michaelis mentis values?
Slide 10 L12
Uses double reciprocal of rate and concentration to place Vmax and Km on the X and Y intercepts
Used to visualize the mechanism of inhibition a compound may exert on an enzyme
What is competitive inhibition, uncompetitive inhibition, and non-competitive inhibition?
Competitive inhibition- a compound binds the active site of the enzyme and excludes the reactant
Slide 13-14 L13
Uncompetitive inhibition- a compound binds the ES complex and slows release to E + P
Slide 16-17 L13
Non-competitive inhibition- a compound binds the enzyme and decreases the rate the enzyme can bind to or react with the substrate
Slide 18-19 L13
What could happen with competitive inhibition if an enzyme has 2 or more possible substrates?
One substrate may act as a competitive inhibitor for the other
Someone consumes methanol (or even spills it on their skin)
Alcohol dehydrogenase converts
Ethanol treats methanol poisoning
