3. AP Biology 2007-2008 Metabolism & Enzymes

4. AP Biology From food webs to the life of a cell energy

5. AP Biology Flow of energy through life  Life is built on chemical reactions  transforming energy from one form to another organic molecules  ATP & organic molecules sun solar energy  ATP & organic molecules

6. AP Biology Metabolism  Chemical reactions of life  forming bonds between molecules  dehydration synthesis  synthesis  anabolic reactions  breaking bonds between molecules  hydrolysis  digestion  catabolic reactions That’s why they’re called anabolic steroids!

7. AP Biology Examples  dehydration synthesis (synthesis)  hydrolysis (digestion) + H2OH2O + H2OH2O enzyme

8. AP Biology Examples  dehydration synthesis (synthesis)  hydrolysis (digestion) enzyme

9. AP Biology Chemical reactions & energy  Some chemical reactions release energy  exergonic  digesting polymers  hydrolysis = catabolism  Some chemical reactions require input of energy  endergonic  building polymers  dehydration synthesis = anabolism digesting molecules= LESS organization= lower energy state building molecules= MORE organization= higher energy state

10. AP Biology Endergonic vs. exergonic reactions exergonicendergonic - energy released - digestion - energy invested - synthesis -G-G  G = change in free energy = ability to do work +G+G

11. AP Biology Energy & life  Organisms require energy to live  where does that energy come from?  coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy) ++ energy + + digestion synthesis

12. AP Biology (a) The structure of ATP Phosphate groups (b) The hydrolysis of ATP Adenine Ribose Energy Adenosine triphosphate (ATP) Adenosine diphosphate (ADP) Inorganic phosphate The bonds between the phosphate groups of ATP can be broken by hydrolysis. –Energy is released from ATP when the terminal phosphate bond is broken. This release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves.

13. AP Biology How the Hydrolysis of ATP Performs Work  The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP.  In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction.  Overall, the coupled reactions are exergonic.

14. AP Biology (a) Glutamic acid conversion to glutamine Glutamic acid  G Glu   3.4 kcal/mol Glutamine (b) Conversion reaction coupled with ATP hydrolysis (c) Free-energy change for coupled reaction Ammonia Glutamic acid Glutamine Phosphorylated intermediate  G Glu   3.4 kcal/mol  G ATP  −7.3 kcal/mol  G Glu   3.4 kcal/mol  G ATP  −7.3 kcal/mol   G  −3.9 kcal/mol Net

15. AP Biology  ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant.  The recipient molecule is now called a phosphorylated intermediate.  ATP hydrolysis leads to a change in a protein’s shape and often its ability to bind to another molecule.

16. AP Biology The Regeneration of ATP  ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP).  The energy to phosphorylate ADP comes from catabolic reactions in the cell.  The ATP cycle is a revolving door through which energy passes during its transfer from catabolic to anabolic pathways.

17. AP Biology What drives reactions?  If reactions are “downhill”, why don’t they just happen spontaneously?  because covalent bonds are stable bonds Why don’t stable polymers spontaneously digest into their monomers? starch

18. AP Biology Activation energy  Breaking down large molecules requires an initial input of energy  activation energy  large biomolecules are stable  must absorb energy to break bonds energy cellulose CO 2 + H 2 O + heat

19. AP Biology Too much activation energy for life  Activation energy  amount of energy needed to destabilize the bonds of a molecule  moves the reaction over an “energy hill” Not a match! That’s too much energy to expose living cells to! glucose

20. AP Biology Reducing Activation energy  Catalysts  reducing the amount of energy to start a reaction Pheeew… that takes a lot less energy! reactant product uncatalyzed reaction catalyzed reaction NEW activation energy

21. AP Biology Catalysts  So what’s a cell got to do to reduce activation energy?  get help! … chemical help… ENZYMES GG Call in the ENZYMES!