AP Biology · Summary

Unit 3 summary

1. Enzymes lower activation energy; they do not change the free energy a reaction releases, and they come out of each reaction unchanged.
2. Rate rises with temperature up to an optimum, then falls as the enzyme denatures; each enzyme also has an optimum pH.
3. More substrate raises the rate until the active sites are nearly all busy. Extra substrate can outcompete a competitive inhibitor, but not an inhibitor bound outside the active site.
4. ATP hydrolysis is exergonic; coupling it to an endergonic step makes the total free-energy change negative.
5. Photosynthesis: the light-dependent reactions in the thylakoids split water, release oxygen and make ATP and NADPH; the Calvin cycle in the stroma uses them to fix CO2 into sugar.
6. Respiration: glycolysis in the cytosol nets 2 ATP; the Krebs cycle in the matrix releases CO2 and makes NADH and FADH2; the chain and ATP synthase make most of the ATP, with oxygen as the final electron acceptor.
7. Without oxygen, fermentation regenerates NAD+ so glycolysis keeps making 2 ATP per glucose.