Cellular Respiration: Harvesting Chemical Energy

1. Cellular Respiration: Harvesting Chemical Energy

2. Cellular Respiration • Glycolysis • The Kreb Cycle (Citric Cycle) • Electron Transport Chain (Chemiosmosis and oxidative phosphorylation)

3. Cellular Respiration • Cells harvest chemical energy stored in molecules and use this to generate ATP. • Organic compounds store energy in their arrangements of atoms.

4. Catabolic (releases energy) • Exergonic (- G, products store less energy than reactants) • Occurs mostly in the mitochondria (but first step is in cytosol) • C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP and heat)

5. General Points • Phosphorylation: the transfer of a phosphate molecule • the production of ATP (adenosine triphosphate) • ADP + P i ATP • Oxygen is very electronegative (i.e. it wants electrons ...think of its Bohr model)

6. Redox Reaction Recap • Involves the transfer of electrons • LEO (loss of electrons)  oxidation (less -) • GER (gain of electrons)  reduction (more -) • Electron donor (reducing agent) the atom that becomes less negative (positive) • Electron acceptor (oxidizing agent) the atom that becomes more negative

7. Sodium and Chlorine (think of the Bohr Models) • Which atom is the electron donor? Acceptor/ • Which atom is the reducing agent? Oxidizing agent?

9. Overview of Cellular Respiration • Step by step process that releases energy along the way (does not release all energy at once) • Hydrogen atoms are stripped away from glucose • Hydrogen atoms ultimate destination is the oxygen molecule • First they are transferred to a coenzyme NAD+ • NAD + wants to gain electrons (to be neutral)

11. NAD + traps electrons from glucose using dehydrogenase (enzyme) which removes a pair of hydrogen atoms from glucose • STOP and THINK of a Bohr model for hydrogen: How many electrons? How many protons?

12. So if we removed two hydrogen atoms, that means we remove two electrons and two protons • C6H12O6

13. Enzyme gives two electrons and one proton to its coenzyme NAD + forming NADH • The other proton (left over) is released into the surrounding environment • Is NAD+ an electron acceptor or donor? • Is NAD+ an oxidizing agent or a reducing agent? **NAD+ is the most versatile electron acceptor in cell resp.

15. Little potential energy is lost when e- are transferred from glucose (food) to NAD+ • NADH molecules represent stored energy that can be used to make ATP when e- complete their “fall” to oxygen • An electron transport chain is used to break the fall of electrons to oxygen • Produces several energy releasing steps NOT one big explosion of energy

17. Pathway of Electrons • Electrons (from glucose in the form of hydrogen atoms) move to  NAD+  NADH  oxygen (final electron acceptor)

18. Glycolysis(“splitting of sugar”) • Glucose is split into two, three carbon sugars called pyruvate • Catabolic pathway (breakdown) • Occurs in the cytosol • Two major phases • Energy investment (puts in 2 ATP) • Energy payoff (creates 4 ATP) • Produces a net result of 2 molecules of usable ATP • Produces 2 molecules of NADH • Can occur without the presence of oxygen

19. glycolysis

20. Oxidizing Glucose • The oxidation of glucose allows energy to be taken out of storage and make energy available to make ATP. • Glucose is broken down gradually in a series of steps catalyzed by an enzyme: dehydrogenase • Hydrogen atoms are stripped from glucose and passed to a coenzyme: NAD + (oxidizing agent)

21. The dehydrogenase removes two hydrogen atoms from the glucose (2 p+ and 2e-) • NAD+ traps 2e- and 1p+ from glucose break down = NADH • NADH-stored energy ready to make ATP when e- complete their journey to oxygen.