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AP Biology John D. O’Bryant School of Mathematics and Science October 12, 2012 AP Biology Agenda Do Now (Quiz) Enzyme Action (lecture) “Why is Patrick Paralyzed?” (case study) “Lorenzo’s Oil” (?) AP Biology Do Now (Quiz) 1. Anything that prevents ATP formation will most likely A) result in cell death. B) force the cell to rely on lipids for energy. C) result in the conversion of kinetic energy to potential energy. D) force the cell to rely on ADP for energy. E) have no effect on the cell. AP Biology Do Now (Quiz) 2. Which of the following statements regarding enzyme function is false? A) An enzyme's function depends on its three-dimensional shape. B) Enzymes are very specific for certain substrates. C) Enzymes are used up in chemical reactions. D) Enzymes emerge unchanged from the reactions they catalyze. E) An enzyme binds to its substrate at the enzyme's active site. AP Biology Do Now (Quiz) 3. If an enzyme solution is saturated with substrate, the most effective way to obtain a faster yield of products is to A) add more of the enzyme. B) heat the solution to 90°C. C) add more substrate. D) add an allosteric inhibitor. E) add a noncompetitive inhibitor. AP Biology Do Now (Quiz) 4. Which of the following will have no effect on the rate of an enzyme-catalyzed reaction? A) temperature B) pH C) competitive inhibitors D) noncompetitive inhibitors E) net change in energy AP Biology Do Now (Quiz) 5. Inhibition of an enzyme is irreversible when A) a competitive inhibitor is involved. B) a noncompetitive inhibitor is involved. C) the shape of the enzyme is changed. D) covalent bonds form between inhibitor and enzyme. E) weak interactions form between inhibitor and enzyme. AP Biology Do Now (Quiz) 6. Bacterial production of the enzymes needed for the synthesis of the amino acid tryptophan declines with increasing levels of tryptophan and increases as tryptophan levels decline. This is an example of A) competitive inhibition. B) noncompetitive inhibition. C) feedback inhibition. D) positive feedback. E) irreversible inhibition. AP Biology Do Now (Quiz) 7. If an enzyme is added to a solution where its substrate and product are in equilibrium, what would occur? A) Additional product would be formed. B) Additional substrate would be formed. C) The reaction would change from endergonic to exergonic. D) The free energy of the system would change. E) Nothing; the reaction would stay at equilibrium. AP Biology Metabolism & Enzymes AP Biology 2007-2008 Factors that Affect Enzymes AP Biology 2007-2008 Factors Affecting Enzyme Function Enzyme concentration Substrate concentration Temperature pH Salinity Activators Inhibitors AP Biology catalase Enzymes and temperature Different enzymes function in different organisms in different environments reaction rate human enzyme hot spring bacteria enzyme 37°C AP Biology temperature 70°C (158°F) How do ectotherms do it? AP Biology pH What’s happening here?! trypsin reaction rate pepsin pepsin trypsin 0 AP Biology 1 2 3 4 5 6 pH 7 8 9 10 11 12 13 14 Factors affecting enzyme function pH changes in pH adds or remove H+ disrupts bonds, disrupts 3D shape disrupts attractions between charged amino acids affect 2° & 3° structure denatures protein (end 10/11) optimal pH? most human enzymes = pH 6-8 depends on localized conditions pepsin (stomach) = pH 2-3 trypsin (small intestines) = pH 8 AP Biology 0 1 2 3 4 5 6 7 8 9 10 11 Salinity reaction rate What’s happening here?! salt concentration AP Biology Factors affecting enzyme function Salt concentration changes in salinity adds or removes cations (+) & anions (–) disrupts bonds, disrupts 3D shape disrupts attractions between charged amino acids affect 2° & 3° structure denatures protein enzymes intolerant of extreme salinity Dead Sea is called dead for a reason! AP Biology Compounds which help enzymes Fe in Activators hemoglobin cofactors non-protein, small inorganic compounds & ions Mg, K, Ca, Zn, Fe, Cu bound within enzyme molecule coenzymes non-protein, organic molecules bind temporarily or permanently to enzyme near active site AP Biology many vitamins NAD (niacin; B3) FAD (riboflavin; B2) Coenzyme A Mg in chlorophyll Compounds which regulate enzymes Inhibitors molecules that reduce enzyme activity competitive inhibition noncompetitive inhibition irreversible inhibition feedback inhibition AP Biology Competitive Inhibitor Inhibitor & substrate “compete” for active site penicillin blocks enzyme bacteria use to build cell walls disulfiram (Antabuse) treats chronic alcoholism blocks enzyme that breaks down alcohol severe hangover & vomiting 5-10 minutes after drinking Overcome by increasing substrate concentration AP Biology saturate solution with substrate so it out-competes inhibitor for active site on enzyme Non-Competitive Inhibitor Inhibitor binds to site other than active site allosteric inhibitor binds to allosteric site causes enzyme to change shape conformational change active site is no longer functional binding site keeps enzyme inactive some anti-cancer drugs inhibit enzymes involved in DNA synthesis stop DNA production stop division of more cancer cells cyanide poisoning irreversible inhibitor of Cytochrome C, an enzyme in cellular respiration stops production of ATP AP Biology Irreversible inhibition Inhibitor permanently binds to enzyme competitor permanently binds to active site allosteric permanently binds to allosteric site permanently changes shape of enzyme nerve gas, sarin, many insecticides (malathion, parathion…) cholinesterase inhibitors AP Biology doesn’t breakdown the neurotransmitter, acetylcholine Allosteric regulation Conformational changes by regulatory molecules inhibitors keeps enzyme in inactive form activators keeps enzyme in active form AP Biology Conformational changes Allosteric regulation Metabolic pathways ABCDEFG 5 6 enzyme enzyme enzyme enzyme enzyme enzyme enzyme 1 2 3 4 Chemical reactions of life are organized in pathways AP Biology divide chemical reaction into many small steps artifact of evolution efficiency intermediate branching points control = regulation Efficiency Organized groups of enzymes enzymes are embedded in membrane and arranged sequentially Link endergonic & exergonic reactions Whoa! All that going on in those little mitochondria! AP Biology Feedback Inhibition Regulation & coordination of production product is used by next step in pathway final product is inhibitor of earlier step allosteric inhibitor of earlier enzyme feedback inhibition no unnecessary accumulation of product ABCDEFG 1 2 3 4 5 6 X enzyme enzyme enzyme enzyme enzyme enzyme AP Biology allosteric inhibitor of enzyme 1 threonine Feedback inhibition Example synthesis of amino acid, isoleucine from amino acid, threonine isoleucine becomes the allosteric inhibitor of the first step in the pathway as product accumulates it collides with enzyme more often than substrate does AP Biology isoleucin e Don’t be inhibited! Ask Questions! AP Biology 2007-2008 Cooperativity Substrate acts as an activator substrate causes conformational change in enzyme induced fit favors binding of substrate at 2nd site makes enzyme more active & effective hemoglobin Hemoglobin 4 polypeptide chains can bind 4 O2; 1st O2 binds now easier for other O2 to bind AP3Biology Lorenzo’s Oil AP Biology