Enzymes: Catalysts of Life

1. CH 6:Metabolism & Enzymes

2. Metabolism  Chemical Reactions of Life • forming bonds between molecules • dehydration synthesis • “anabolic” or “endergonic”  turn in energy • breaking bonds between molecules • Hydrolysis/digestion • “catabolic” or “exergonic”  release energy

3. Where does energy come from? • coupling Pair exergonic reactions (out) with endergonic reactions (in) energy + + energy + +

4. Reactions aren’t spontaneous … • covalent bonds are stable bonds • need to absorb energy to start

5. energy Activation energy • Def: Energy required to start a reaction • Enzymes act as catalysts and reduce activation energy cellulose CO2 + H2O + heat

6. Enzymes • Catalysts • proteins • Jump start chemical reactions • required for most biological reactions • highly specific  1000s of different enzymes in cells

7. vocab substrate • reactant that binds to enzyme • enzyme-substrate complex: temporary active site • enzyme’s catalytic site; substrate fits into active site product • end result active site products substrate enzyme

8. Properties of enzymes • Reaction specific • each enzyme works with a specific substrate • Not consumed in reaction • Affected by cellular conditions denature in wrong conditions

9. Named for reaction • sucrase breaks down sucrose • lipases break down lipids • DNA polymerase builds DNA

10. Lock and Key Model [very simple] • substrate fits into enzyme active site • H bonds between substrate & enzyme

11. Induced fit model [better] • 3-D structure of enzyme fits substrate • binding cause enzyme to change shape leading to a tighter fit • “conformational change”

12. How do enzymes work? • In Synthesis Rxn. . . • active site orients substrate in correct position for reaction • enzyme brings substrate closer together • In Hydrolysis Rxn … • active site binds substrate & puts stress on bonds that must be broken easier to separate molecules

13. Factors Affecting Enzyme Function • enzyme concentration • substrate concentration • temperature • pH • salinity (ionic conditions) • activators • inhibitors catalase

14. reaction rate enzyme concentration Enzyme Concentration • as  enzyme =  reaction rate • more enzymes = collide more often with substrate • Eventually reaction rate levels off • Why? substrate becomes limiting factor • not all enzyme molecules can find substrate

15. reaction rate substrate concentration Substrate Concentration • as  substrate =  reaction rate • more substrate = collide more often with enzyme • Eventually reaction rate levels off (max rate) • all enzymes have active site engaged • enzyme is saturated

16. Temperature • Optimum T° • greatest # of collisions • human enzymes = 35°- 40°C • Heat: increase beyond optimum T° • H bonds between enzyme & substrate break • denaturation = lose 3D shape (3° structure) • Cold: • molecules slower • decrease collisions between enzyme & substrate

17. 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)

18. 0 1 2 3 4 5 6 7 8 9 10 11 pH • changes in pH • disrupts bonds, disrupts 3D shape • affect 2° & 3° structure • denatures protein • optimal pH • most human enzymes = pH 6-8 • depends on local conditions • pepsin (stomach) = pH 2-3 • trypsin (small intestines) = pH 8

19. 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

20. Salinity • changes in salinity add/remove cations (+) & anions (–) • disrupts bonds, disrupts 3D shape • affect 2° & 3° structure • denatures protein • enzymes intolerant of extreme salinity • Dead Sea = dead