2. AP Biology Metabolism and Energy

3. AP Biology Metabolic reactions & energy  Some chemical reactions release energy  exergonic  breaking 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

4. AP Biology Examples  dehydration synthesis  hydrolysis

5. AP Biology 2005-2006 Endergonic vs. exergonic reactions exergonicendergonic energy releasedenergy invested GG  G = change in free energy = ability to do work

6. 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 + +

7. AP Biology 2005-2006 Spontaneous reactions?  If reactions are “downhill”, why don’t they just happen spontaneously?  because covalent bonds are stable Why don’t polymers (carbohydrates, proteins & fats) just spontaneously digest into their monomers

8. 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

9. AP Biology Activation energy  the amount of energy needed to start the reaction.  moves the reaction over an “energy hill”

10. AP Biology 2005-2006 Catalysts  So what’s a cell to do to reduce activation energy?  get help! … chemical help… Call in the... ENZYMES! ENZYMES GG

11. AP Biology 2005-2006 Energy needs of life  Organisms are endergonic systems  What do we need energy for?   synthesis (biomolecules)  reproduction  active transport  movement  temperature regulation

12. AP Biology Living economy  Fueling the economy  eat high energy organic molecules (food)  break them down = catabolism (digest)  capture energy in form cell can use  Need an energy currency  a way to pass energy around ATP Whoa! Hot stuff!

13. AP Biology 2005-2006 ATP  Adenosine Triphosphate  modified nucleotide  adenine + ribose + P i  AMP  AMP + P i  ADP  ADP + P i  ATP an RNA nucleotide How efficient! Build once, use many ways

14. AP Biology 2005-2006 Why does ATP store energy? P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O  Each P i group more difficult to add  a lot of stored energy in each bond  most stored in 3rd P i  Phosphorylation...  Storing energy with ATP Why is the 3 rd phosphate like a bad boyfriend?  spring-loaded instability of its P bonds makes ATP an excellent energy donor

15. AP Biology 2005-2006 An example of Phosphorylation…  Building polymers from monomers  need ATP for energy & to take the water out C H OH H OHOH C C H O H C + H2OH2O + +4.2 kcal/mol C H OH + C H P + ATPADP -7.3 kcal/mol H OHOH C C H O H C + + C H P PiPi -3.1 kcal/mol “kinase” enzyme

16. AP Biology 2005-2006 ATP / ADP cycle A working muscle recycles over 10 million ATPs per second Can’t store ATP  too reactive  transfers P i too easily  only short term energy storage  carbs & fats are long term energy storage Coupling of exergonic and endergonic reactions.

17. AP Biology What’s the point?  Cells spend a lot of time making ATP! “The point is to make ATP!” For chemical, mechanical, and transport work I didn’t HEAR you! Make ATP! That’s all I do all day. And no one even notices!