AP Biology John D. O’Bryant School of Mathematics and Science

1. AP BiologyJohn D. O’Bryant School of Mathematics and Science October 15, 2012

2. Agenda • Do Now (Quiz) • “Why is Patrick Paralyzed?” (case study) • Exam 1 discussion • “Lorenzo’s Oil” (?)

3. 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.

4. 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.  

5. 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

6. 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.

7. 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.

8. 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.

9. 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

10. Metabolism & Enzymes

11. Factors that Affect Enzymes

12. Factors Affecting Enzyme Function • Enzyme concentration • Substrate concentration • Temperature • pH • Salinity • Activators • Inhibitors catalase

13. 37°C 70°C Enzymes and temperature • Different enzymes function in different organisms in different environments hot springbacteria enzyme human enzyme reaction rate temperature (158°F)

14. How do ectotherms do it?

15. pH What’shappening here?! pepsin trypsin pepsin reaction rate trypsin 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH

16. 0 1 2 3 4 5 6 7 8 9 10 11 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

17. Salinity What’shappening here?! reaction rate salt concentration

18. 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!

19. Compounds which help enzymes Fe inhemoglobin • 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 toenzyme near active site • many vitamins • NAD (niacin; B3) • FAD (riboflavin; B2) • Coenzyme A Mg inchlorophyll

20. Compounds which regulate enzymes • Inhibitors • molecules that reduce enzyme activity • competitive inhibition • noncompetitive inhibition • irreversible inhibition • feedback inhibition

21. Competitive Inhibitor • Inhibitor & substrate “compete” for active site • penicillinblocks enzyme bacteria use to build cell walls • disulfiram (Antabuse)treats chronic alcoholism • blocks enzyme that breaks down alcohol • severe hangover & vomiting5-10 minutes after drinking • Overcome by increasing substrate concentration • saturate solution with substrate so it out-competes inhibitor for active site on enzyme

22. Non-Competitive Inhibitor • Inhibitor binds to site other than active site • allosteric inhibitorbinds toallosteric site • causes enzyme to change shape • conformational change • active site is no longer functional binding site • keeps enzyme inactive • some anti-cancer drugsinhibit enzymes involved in DNA synthesis • stop DNA production • stop division of more cancer cells • cyanide poisoningirreversible inhibitor of Cytochrome C, an enzyme in cellular respiration • stops production of ATP

23. 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

24. Allosteric regulation • Conformational changes by regulatory molecules • inhibitors • keeps enzyme in inactive form • activators • keeps enzyme in active form Conformational changes Allosteric regulation

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

26. Efficiency • Organized groups of enzymes • enzymes are embedded in membrane and arranged sequentially • Link endergonic & exergonic reactions Whoa!All that going onin those littlemitochondria!

27.       enzyme 1 enzyme 2 enzyme 3 enzyme 4 enzyme 5 enzyme 6 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 G X allosteric inhibitor of enzyme 1

28. 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 isoleucine

29. Don’t be inhibited!Ask Questions!

30. 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 3 O2 to bind

31. Lorenzo’s Oil