1. DO NOW: Which of the following reactions could be coupled to the reaction: ATP + H 2 O  ADP + P i (-7.3 kcal) a. A + P i  AP (+ 9.3 kcal) b. B + P i  BP (+ 8 kcal) c. CP  C + P i (- 4 kcal) d. DP  D + P i (-10 kcal) e. E + P i  EP (+ 5 kcal)

3. What are enzymes?  Biological catalysts Most are proteins Some RNA (called??)  Regulate metabolism  Respond to changing needs of cell

4. All reactions require activation energy…  E A - needed to break existing bonds Even exergonic reactions require E A  Enzymes lower E A Allow reactions to occur more quickly http://www.stolaf.edu/people/giannini/flashanimat/enzymes/transition%20state.swf  Enzymes reduce reliance on random collision of reactants http://www.stolaf.edu/people/giannini/flashanimat/enzymes/prox-orien.swf

5. Do enzymes change the free energy of the products or reactants?

6. Lock & Key or Induced Fit? http://www.stolaf.edu/people/giannini/flashanimat/enzymes/enzyme.swf

7. Specificity – why?? Are enzymes changed in the reaction? Why is this important?

8. Cofactors  Some enzymes have 2 components Apoenzyme – protein Cofactor – additional component Alone, neither is catalytic  Cofactors may be. Inorganic – Ca, Mg, trace elements Coenzymes – organic, nonpeptide ○ Carrier molecules ○ ATP ○ Vitamins

9. Enzymes work best under specific conditions  Temperature In humans, most 35 o C - 40 o C Low temps: What effect? Why? High temps: What effect?

10.  pH Humans, 6-8 Some work in low pH – Example? Buffers  Change in pH alters electric charges in R-groups of enzymes  denature  How does salt concentration affect enzyme shape??

11. Metabolic Pathways What is a metabolic pathway? Enzymes aid in reaction coupling Work in sequence Product of 1 enzyme, the reactant in next A enzyme 1 > B enzyme 2 > C

12.  Each reaction is reversible, but… Intermediate and final products are removed Drives the sequence of reactions to the right

13. Enzyme Complexes  Assemblage of multiple enzymes into 1 complex Enzymes of pathway Arrangement facilitates sequence of reactions ○ Structure & Function  Some have fixed locations within membranes  Others in solution inside specific organelles

14. Why does enzyme activity need to be regulated? How can it be regulated?

15. How can Enzyme Activity be Regulated?  Synthesis of enzyme Gene turned on/off by signal  Substrate concentration If excess substrate, enzyme conc. is limiting factor Low conc. of substrate can be rate-limiting factor also  Inactive pre-cursors Ex. Pepsin

18. Feedback Inhibition  Product of one enzymatic reaction controls the activity of another  If product later in pathway inhibits an enzyme earlier in reaction sequence = feedback inhibition A enzyme 1 >B enzyme 2 >C enzyme 3 >D enzyme 4 >E

19. Exit ticket:  Why is maintaining homeostasis important to an enzyme’s ability to function?