Objectives & Announcements for Friday, September 16

1. Objectives & Announcementsfor Friday, September 16 • Objectives: • Continue Energy & Metabolism • Readings for today carry over through Mon. & Wed. • Announcements: • Exam I answer key will be posted on Web site and outside 252 Davenport Hall (DH) by 3:00 PM today • If you have questions about the actual grading of your exam, please direct them to Melissa Reedy in 208 Noyes • If you have questions about the problems on the exam, please visit my office hours (do not email or post on LON-CAPA) • If you took the conflict exam, you may pick up your copy of the exam in 252 Davenport Hall at your convenience • Group tutoring begins next week; see Twitter for details

2. So how does the energy from food get to ATP? CELLULAR RESPIRATION • Breakdown of glucose to CO2 and H2O • Multiple reactions in 3 distinct pathways (phases) • Glycolysis • Pyruvate Oxidation & The Krebs (or Citric Acid) Cycle • Electron Transport Chain & Oxidative Phosphorylation • Let’s follow the path of energy and molecules from glucose to ATP…

3. Glycolysis • First pathway in breakdown of glucose • "glyco" (sugar) + "lysis" (splitting) • starts with a 6-carbon sugar (glucose), ends with two 3-carbon molecules (pyruvate) • Pathway is actually endergonic up to production of first 3-carbon molecules (uses cell's store of ATP) • Occurs in the cytoplasm of all living cells

4. Glycolysis • 2 steps are endergonic • 3 steps are exergonic • E from first exergonic step harnessed by transfer of e- to NAD+ (E not used to directly synthesize ATP, but it’s “saved” and used later) • E from other exergonic rxns is in form of P, which is used to phosphorylate ADP > SLP

5. Problems at end of Glycolysis: • Still aren't at lowest energy state (most E still in pyruvate) • NAD+ is used up but not recycled, and is still holding on to a lot of our energy (will be released when NADH gets oxidized) • How is energy in pyruvate released? • How is NAD+ replaced? • How is energy in NADH transferred to ATP? • If oxygen is present: • Aerobic Respiration • If oxygen is not present: • Anaerobic Respiration (Fermentation)

6. Aerobic Respiration • Carbon source (2 molecules of pyruvate) completely converted to carbon dioxide • only happens in presence of oxygen • pyruvate molecules are converted to acetyl-CoA, which then enters the Krebs (or Citric Acid) Cycle • all C-H bonds converted to C-O bonds (6 CO2 released) • energy transferred to NAD+ and FAD (makes more NADH & FADH2) • another SLP reaction in Krebs cycle (GTP is ATP analog) • Where does aerobic respiration take place? • Mitochondria of eukaryotic cells • Cytoplasm and plasma membrane of prokaryotes

7. Cristae Inner Membrane Matrix Outer Membrane • The Mitochondria

8. Inner Membrane Outer Membrane Intermembrane Space Matrix • Organization of the Mitochondria: – Principle site of ATP generation – >70% protein! – Impenetrable to ions/small molecules except at transporters – Typical protein % – Porins – Composition of ions and small molecules is same as cytoplasm – Krebs cycle enzymes – pyruvate gets brought into the matrix

9. Pyruvate Oxidation & Krebs (Citric Acid) Cycle: • 6 CO2 • 8 NADH • 2 FADH2 • 2 GTP (2 ATP)

10. Results of Krebs Cycle for every 2 pyruvate: • 8 more NADH • 2 FADH2 • 2 GTP (which are equivalent in energy to ATP) CO2, NADH GTP

11. Problems with results of Krebs Cycle: • Still haven't replaced NAD+; in fact, more NADH is made • Now you have FADH2 that needs to be re-oxidized • Still haven't transferred energy carried by cofactors to ATP • Also, why is this dependent on oxygen? • Aerobic respiration requires oxygen, but Krebs cycle itself does not • Because Krebs cycle is coupled to the third pathway which does require oxygen –– ETC

12. Electron Transport Chain • ETC is a series of "electron carriers" in membranes: • in prokaryotes – cytoplasmic membrane • in eukaryotes – inner mitochondrial membrane