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Bell-Ringer

Bell-Ringer. What is consumed in cellular respiration? Glucose (or other organic molecule), O 2 What is produced in cellular respiration? H 2 O, CO 2 , energy (heat + ATP) Where does cellular respiration occur? Mostly in mitochondria What can we say about glucose in cellular respiration ?

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Bell-Ringer

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  1. Bell-Ringer • What is consumed in cellular respiration? • Glucose (or other organic molecule), O2 • What is produced in cellular respiration? • H2O, CO2, energy (heat + ATP) • Where does cellular respiration occur? • Mostly in mitochondria • What can we say about glucose in cellular respiration? • It gets oxidized, it loses e-’s, it is a reducing agent • What can we say about oxygen in cellular respiration? • It gets reduced, it gains e-’s, it is an oxidizing agent

  2. Cellular Respiration: Glycolysis & the Krebs CycleCh. 9 Ms. Springstroh AP Biology Adapted from Ms. Gaynor-Day and Mr. Grant

  3. becomes oxidized C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes reduced Oxidation of Organic Fuel Molecules During Cellular Respiration • During cellular respiration • Glucose is oxidized(loses e-’s) • oxygenis reduced (gains e-’s) • Electrons always travel with a hydrogen, so we see this as the oxygen gaining hydrogens • E-’s lose potential energy  energy is released http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/ets_flash.html

  4. Electronsare not transferred directly from glucose to oxygen but are passed first to a coenzyme called NAD+orFAD • NAD+ and FAD= • e- acceptors/capturers/ oxidizing agents • Accept e-’s (& the H+’s they travel with) from glucose

  5. When NAD+ or FAD accept electrons (get reduced), they become NADH and FADH2, respectively. • This is because electrons always travel with an H+

  6. Let’s review… • e-’s are relocated during catabolic rxns (ie. cellular respiration), in order to provide energy • The ultimate transfer: At first, e-’s are in food (ie. glucose). At the end, the e-’s (& the H+’s they travel with) meet up w/ oxygen to form H2O. • But before they meet oxygen, e-’s are first transferred to NAD+ or FAD.

  7. How does NAD+ take the electrons from food (ie. glucose) and ultimately give them to oxygen? NADH drops these electrons off at the electron transport chain, which breaks the fall of electrons to oxygen into several energy-releasing steps.

  8. 2 H + 1/2 O2 (from food via NADH) Controlled release of energy for synthesis ofATP 2 H+ + 2 e– ATP ATP Free energy, G Electron transport chain ATP 2 e– 1/2 O2 2 H+ H2O Electron Flow = (b) Cellular respiration food  NADH/FADH2 ETC  oxygen

  9. The Stages of Cellular Respiration • Respiration is a cumulative process of 3 metabolic stages 1. Glycolysis 2. The citric acid cycle 3. Oxidative phosphorylation

  10. The 3 Stages • Glycolysis • Rearranges bonds in glucose (6C) to form 2 molecules of pyruvate (3C) • Releases free energy which forms ATP • Also produces NADH, which will be involved in the production of ATP later • Kreb’s Cycle (Citric acid cycle) • Completes the breakdown of glucose & forms CO2 • Makes ATP • Also produces NADH, which will be involved in the production of ATP later • Electrons are captured by coenzymes • Oxidative phosphorylation • NADH & FADH2 drop their e-’s off at the electron transport chain • Generates ATP

  11. Electrons carried via NADH and FADH2 Electrons carried via NADH Oxidativephosphorylation:electron transport andchemiosmosis Citric acid cycle Glycolsis 2 Pyruvate Glucose Cytoplasm Mitochondrion Matrix ATP ATP ATP Substrate-level phosphorylation Oxidative phosphorylation Substrate-level phosphorylation Figure 9.6 • An overview of cellular respiration Inner Mitochondrion Membrane (Cristae)

  12. Stage #1: Glycolysis • Glycolysis produces energy by oxidizing glucose & rearranging glucose’s bonds to form pyruvate • Glycolysis • Means “splitting of sugar” • Breaks down glucose (6C) into pyruvate (3C) • Occurs in the cytoplasmof the cell • Produces ATP via substrate-level phosphorylation

  13. Substrate-level phosphorylation • An enzyme takes a phosphate from a phosphorylated substrate and transfers it to ADP • Substrate was generated during the catabolism (break down) of glucose • Forms ATP • Utilized in both glycolysis & Kreb’s cycle

  14. Glycolysis Oxidativephosphorylation Citricacidcycle ATP ATP ATP Energy investment phase 1 Glucose 2 ADP + 2 used P 2 ATP Energy payoff phase formed 4 ATP 4 ADP + 4 P 2 NAD+ + 4 e- + 4 H + 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Glucose 2 Pyruvate + 2 H2O 4 ATP formed – 2 ATP used 2 ATP + 2 H+ 2 NADH 2 NAD+ + 4 e– + 4 H + • Glycolysis consists of two major phases • Energy investment phase • Uses 2 ATP • Endergonic 2. Energy payoff phase • Produces 4 ATP & NADH • Exergonic

  15. Glycolysis NET • Glucose  2 pyruvate (pyruvic acid) + 2 H2O • 4 ATP formed – 2 ATP used  2 ATP GAIN • substrate-level phosphorylation used • NAD+  NADH **Glycolysis can proceed WITHOUT O2

  16. glucose      pyruvate 6C 3C 2x Glycolysis (stage 1) is only the start • Glycolysis rearranges glucose’s bonds  pyruvate • Pyruvate has more energy to yield • More C to strip off (to oxidize) • if O2 is available, pyruvate enters mitochondria • enzymes of Krebs cycle complete the full oxidation of sugar to CO2

  17. Stage 1 ½: Oxidation of Pyruvate • Start with 2 pyruvate (3C) (6C total) from glycolysis • Each one releases 1 CO2 (2 CO2 total) (2C total) • Reduce NAD+ to NADH (moves e-) • End up with 2 acetyl CoA total (4C total) • Acetyl CoA enters Krebs Cycle • Essentially, pyruvate links glycolysis to the Kreb’scycle • Needs to happen before Kreb’s cycle can begin • Takes place in mitochondrion!

  18. MITOCHONDRION CYTOSOL (cytoplasm) NAD+ + H+ NADH O– CoA S 2 C O C O C O CH3 1 3 CH3 CO2 Transport protein Figure 9.10 Stage #1 ½ : Oxidation of Pyruvate oxidation

  19. Stage #2: The Kreb’s Cycle (aka Citric Acid Cycle) • Takes place in the matrix of the mitochondrion **NEEDS O2 TO PROCEED (unlike glycolysis)

  20. The Kreb’s Cycle • Also called the “Citric Acid cycle” • 8-step pathway • Each step catalyzed by a specific enzyme • 2 CO2 is released from each Acetyl CoA • ATP is synthesized from ADP and Pi • NAD+ and FAD (both are coenzymes) = electron “carriers/capturers”; proton acceptors • They become reduced to NADH and FADH2during the Kreb’s cycle and carry e-’s from Kreb’s Cycle to ETC

  21. 4C 3C 5C 6C 2C 4C 4C 6C 4C 4C CO2 CO2 An overview of the Citric Acid Cycle. Count the carbons! pyruvate acetyl CoA citrate This happens twice for each glucose molecule x2

  22. Glycolysis Citricacidcycle Oxidativephosphorylation Pyruvate (from glycolysis,2 molecules per glucose) ATP ATP ATP CO2 CoA NADH + 3 H+ Acetyl CoA CoA CoA Citricacidcycle 2 CO2 3 NAD+ FADH2 FAD 3 NADH + 3 H+ ADP + P i ATP Figure 9.11 An overview of the citric acid cycle (this occurs for EACH pyruvate molecule) Now, count the electron carriers! The electron carriers get reduced!

  23. Remember: NAD+ and FAD Oxidized Form Reduced Form NAD+ NADH FAD FADH2 THINK: FADH2 come into play in the 2nd stage of cellular respiration; it is also the 2nd electron carrier 

  24. Kreb’s Cycle Summary • Stage 1 ½: 2 x [pyruvate  Acetyl-CoA + 1 NADH ] • Each turn of Kreb’s cycle uses 1 pyruvate • So… 1 glucose molecule produces 2 pyruvate = 2 turns of Kreb’s cycle • 1 turn of cycle (including stage 1 ½) yields NADH, 1 ATP, and FADH2and 3 CO2 (as waste product) Remember to multiply by 2…why? • http://www.hippocampus.org/AP%20Biology%20II • Watch Pyruvate

  25. Value of Krebs cycle? • If the yield is only 2 ATP then how was the Krebs cycle an adaptation? • NADH & FADH2 (reduced forms of NAD+ and FAD)are very valuable • electron carriers & H+ carriers • (move electrons and H+) • to be used in the Electron Transport Chain, where much more energy in the form of ATP will be made! like $$in the bank

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