1. Chapter 6.2 Time’s Arroe and the World of Life AP Biology Fall 2010

2. Bell Ringer 1.What prevents chemical reactions from occurring spontaneously?

3. Objectives Describe the difference between an exergonic and endergonic reaction Understand the concept of activation energy Analyze the importance of ATP in the cell and its role in cellular activities

4. Energy In, Energy Out Reactants: starting substances in chemical rxn. Intermediates: substances formed before a rxn. ends Products: substances remaining after a chemical rxn. The energy required to break or form chemical bonds is measured in kilocalories

5. Energy In, Energy Out Endergonic reactions: (energy in) require energy input resulting in products with more energy than the reactants had – Example: photosynthesis

6. Energy In, Energy Out Exergonic reactions: (energy out) release energy such that the products have less energy than the reactants – Example: aerobic respiration

7. Energy In, Energy Out Energy carriers: activate enzymes and other molecules by phosphate-group transfers – ATP Cofactors: metal ions or coenzymes that aid the enzymes by accepting and donating electrons, atoms, and functional groups Transport proteins: affect concentrations of substances of substances by aiding solute movement across membranes, which influence reactions

8. Activation Energy Energy is required to overcome the strength of chemical bonds in reactants Every single reaction has a characteristic activation energy, which is the minimum amount of energy needed to start a reaction

9. ATP- The Cell’s Energy Currency ATP: composed of adenine, ribose, and 3 phosphate groups Most metabolic reactions involve ATP as the coupling agent (energy carrier) Energy input links phosphate to ADP to produce ATP (phosphorylation) ATP can in turn donate a phosphate group to another molecule, which becomes primed and energized for specific reactions

10. ATP- The Cell’s Energy Currency ATP’s role is like currency in an economy – Earning ATP during exergonic reactions and spending it during endergonic ones ADP can be recycled to ATP very rapidly in the ATP/ADP cycle

11. Review 1.Why is ATP described as the currency of cells? 2.Describe the difference between endergonic and exergonic reactions.

12. Answers 1.ATP is the currency of cells because cells can earn ATP during exergonic reactions and spend it during endergonic ones. 2.An endergonic reaction is a reaction that requires energy input, resulting in products with more energy than the reactants had (energy in). An exergonic reaction releases energy such that the products have less energy than the reactants (energy out).