AP Biology AP Biology John D. O’Bryant School of Mathematics and Science October 15, 2012

AP Biology Agenda  Do Now (Quiz)  “Why is Patrick Paralyzed?” (case study)  Exam 1 discussion  “Lorenzo’s Oil” (?)

AP Biology Do Now (Quiz)  1. Some bacteria are metabolically active in hot springs because  A) they are able to maintain a cooler internal temperature. B) high temperatures make catalysis unnecessary. C) their enzymes have high optimal temperatures. D) their enzymes are completely insensitive to temperature. E) they use molecules other than proteins or RNAs as their main catalysts.

AP Biology Do Now (Quiz)  2. Which of the following statements describes enzyme cooperativity? A) A multi-enzyme complex contains all the enzymes of a metabolic pathway. B) A product of a pathway serves as a competitive inhibitor of an early enzyme in the pathway. C) A substrate molecule bound to an active site affects the active site of several subunits. D) Several substrate molecules can be catalyzed by the same enzyme. E) A substrate binds to an active site and inhibits cooperation between enzymes in a pathway.

AP Biology Do Now (Quiz)  3. A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. What is substance X?  A) a coenzyme B) an allosteric inhibitor C) a substrate D) an intermediate E) the product

AP Biology Do Now (Quiz)  4. A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. Substance A functions as  A) a coenzyme. B) an allosteric inhibitor. C) the substrate. D) an intermediate. E) a competitive inhibitor.

AP Biology Do Now (Quiz)  5. The molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction  A) gains electrons and gains energy. B) loses electrons and loses energy. C) gains electrons and loses energy. D) loses electrons and gains energy. E) neither gains nor loses electrons, but gains or loses energy.

AP Biology Do Now (Quiz)  6. Using a series of arrows, draw the branched metabolic reaction pathway described by the following statements.  ∙ L can form either M or N.  ∙ M can form O.  ∙ O can form either P or R.  ∙ P can form Q.  ∙ R can form S.  ∙ O inhibits the reaction of L to form M.  ∙ Q inhibits the reaction of O to form P.  ∙ S inhibits the reaction of O to form R.

AP Biology Do Now (Quiz)  7. According to the figure you created from question 6, which reaction would prevail if both Q and S were present in the cell in high concentrations?  A) L → M  B) M → O  C) L → N  D) O → P  E) R → S

AP Biology Metabolism & Enzymes

AP Biology Factors that Affect Enzymes

AP Biology Factors Affecting Enzyme Function  Enzyme concentration  Substrate concentration  Temperature  pH  Salinity  Activators  Inhibitors catalase

AP Biology Enzymes and temperature  Different enzymes function in different organisms in different environments 37°C temperature reaction rate 70°C human enzyme hot spring bacteria enzyme (158°F)

AP Biology How do ectotherms do it?

AP Biology 7 pH reaction rate pepsintrypsin What’s happening here?! pepsin trypsin

AP Biology 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

AP Biology Salinity salt concentration reaction rate What’s happening here?!

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  Activators  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  many vitamins  NAD (niacin; B3)  FAD (riboflavin; B2)  Coenzyme A Mg in chlorophyll Fe in hemoglobin

AP Biology 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  saturate solution with substrate so it out-competes inhibitor for active site on enzyme

AP Biology 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 doesn’t breakdown the neurotransmitter, acetylcholine

AP Biology Allosteric regulation  Conformational changes by regulatory molecules  inhibitors  keeps enzyme in inactive form  activators  keeps enzyme in active form Conformational changesAllosteric regulation

AP Biology Metabolic pathways A  B  C  D  E  F  GA  B  C  D  E  F  G enzyme 1  enzyme 2  enzyme 3  enzyme 4  enzyme 5  enzyme 6   Chemical reactions of life are organized in pathways  divide chemical reaction into many small steps  artifact of evolution   efficiency  intermediate branching points   control = regulation A  B  C  D  E  F  GA  B  C  D  E  F  G enzyme 

AP Biology 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 allosteric inhibitor of enzyme 1 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 A  B  C  D  E  F  GA  B  C  D  E  F  G enzyme 1  enzyme 2  enzyme 3  enzyme 4  enzyme 5  enzyme 6  X

AP Biology 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 threonine isoleucin e

AP Biology Don’t be inhibited! Ask Questions!

AP Biology Cooperativity  Substrate acts as an activator  substrate causes conformational change in enzyme  induced fit  favors binding of substrate at 2 nd site  makes enzyme more active & effective  hemoglobin Hemoglobin  4 polypeptide chains  can bind 4 O 2 ;  1 st O 2 binds  now easier for other 3 O 2 to bind

AP Biology Lorenzo’s Oil