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Ch 9: Cellular Respiration

Ch 9: Cellular Respiration. The Big Picture. Cellular respiration sole purpose is to produce ATP. Its an exergonic (catabolic)reaction. Can be summarized as a whole as: Organic Compound+Oxygen CO2+Water +ATP + heat.

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Ch 9: Cellular Respiration

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  1. Ch 9: Cellular Respiration

  2. The Big Picture • Cellular respiration sole purpose is to produce ATP. • Its an exergonic (catabolic)reaction. • Can be summarized as a whole as: Organic Compound+OxygenCO2+Water +ATP + heat

  3. Glycolysis, Krebs Cycle, and Oxidative Phosphorylation • 1. Glycolysis is the decomposition of glucose to pyruvate (or pyruvic acid) • 2. Krebs Cycle takes pyruvate (2 pyruvate per glucose molecule) and yields electron acceptors and ATP. • 3. Oxidative phosphorylation extracts ATP from NADH and FADH2.

  4. Reminder on ATP • ATP (adenosine triphosphate) is a nucleotide with unstable phosphate bonds that the cell hydrolyzes for energy. • The cell taps energy stored in ATP by enzy- matically transferring terminal phosphate groups from ATP to other compounds. • The compound receiving the phosphate group is said to be phosphoralated and is more reactive as a result. • Cells use ATP to continue cellular work. But they must replenish the ATP supply to continue cellular work. Respiration does this.

  5. Simply put –cellular respiration is • a redoxprocess that transfers • hydrogen from sugar to oxygen. • Valence electrons of carbon and • hydrogen lose potential energy as • they shift toward electronegative O. • Released energy is used by cells • to produce ATP.

  6. Redox reactions • These are the energy-shuttling mechansisms of metabolism • Partial or complete gain of electrons=reduction • Partial or complete loss of electron=oxidation • They are always coupled…so in order for a material to lose an electron, another molecule must accept it

  7. The NAD+, NADH, FAD+, FADH • NAD+ and FAD+ are coenzymes that function in the redox reactions and are found in all cells. • Traps energy-rich electrons from the organic compound. • NAD+= oxidized coenzyme • NADH= reduced coenzyme Why isn’t glucose oxidized in one explosive step?

  8. During oxydation of glucose, NAD+ functions as an oxidizing agent by trapping energy-rich electrons from glucose. These reactions are catalized byenzymes calleddehydrogenases which: - Remove a pair of hydrogen atoms (2 e,2p) from substrate. • Deliver the two electrons and one proton to NAD+ • Release the remaining proton into the surrounding solution.

  9. Cellular Respiration

  10. Glyclolysis (per glucose molecule) • Takes place in cytosol. • Mutiple steps (9 or 10 depending on source) in the process of decomposing glucose into pyruvate. Mg2+ ions are cofactors to help. • 2 ATP go IN • 4 ATP PRODUCED (so what is NET gain?) • 2 NAD+ go IN • 2 NADH PRODUCED • 2 Pyruvate (Pyruvic acid) PRODUCED

  11. Glycolysis………. - occurs whether O is present or not - no CO2 is released as glucose is oxidized to pyruvate; all C in glu – cose can be accounted for in the 2 molecules of pyruvate. - occurs in 2 phases

  12. Glycolysis: Energy Investment Phase • includes 5 preparatory steps in which • glucose is split in two. • consumes ATP….why? The cell uses ATP to phosphorylate the intermediates of glycolysis. • End result of this phase is 2 molecules • of glyceraldehyde phosphate (3 C each) for each glucose molecule.

  13. Glycolysis: Energy – Yielding Phase • two 3 carbon intermediaries (PGAL) • are oxidized becoming pyruvate. • there’s a net gain of 2 ATPs by • substrate phosphorylation • 2 molecules of NAD+ are reduced to • NADH

  14. Glycolysis • Breaks down “Glucose”(6-carbon sugar)into 2 molecules of “Pyruvic Acid”(3-carbon compound) • The products are: • 2 Pyruvic Acid molecules • 2 ATP molecules • 2 NADH molecules

  15. Glycolysis has 2 pathways… • If Oxygen is present (Aerobic)...“Krebs Cycle”… then to Electron Transport Chain If Oxygen is absent (Anaerobic)…….. “Fermentation”occurs

  16. KREBS Cycle (per pyruvate) • Takes place in mitochondrial matrix. • Pyruvate combines with CoA (coenzyme A) to make acetyl CoA. This makes 1 NADH and 1 CO2. • Acetyl CoA combines with OAA to form citric acid. (8 steps yielding intermediate products). 3 NADH and 1 FADH2 are made and CO2 released. 1 ATP is made. • How much total ATP then for the Krebs cycle?

  17. Junction between gly- • colysis and Krebs Cycle • Is the oxidation of Pyru- • vate to acetyl CoA. • - CO2 is removed from • the carboxyl group of • pyruvate changing it • from a 3 carbon to a • 2 carbon compound. • CO2 is released. • 2 NADH molecules • are produced • Coenzyme A attaches • to the acetyl group – very unstable-reactive

  18. KREBS CYCLE(Aerobic Pathway) • Krebs Cycle oxidizes • the remaining acetyl • fragments of Acetyl – • CoA to CO2. • Energy released from • this exergonic process • is used to reduce co – • enzymes, NAD and • FAD, and phosphory – • late ATP. • How many ATPs are • produced here? • 2 NADH molecules • are produced • Coenzyme A attaches • to the acetyl group – very unstable-reactive

  19. ETC (Oxidative Phosphorylation) • Takes place in inner mitochondrial membrane • Involves a passing of electrons through a series of membrane associated electron carriers in the mitochondria to ultimately produce ATP • You shuffle electrons to pump protons across the mitochondiral membrane against a concentration gradient to help establish a proton gradient

  20. The ETC transports electrons from NADH and FADH2 along a transport chain • The respiratory chain is composed of 4 enzyme complexes and carriers called cytochrome c and ubiquinone (Q). The 1st two complexes shuttle the electrons of NADH + H+ and FADH2 to Q. • The third complex moves electrons from Q to chytochrome c. • The final complex passes electrons to O2, an ultimate acceptor, which results in H20 as a by-product

  21. The chain is an energy converter that pumps H+ across the membrane. How? Certain members along the electron transport chain accept and release protons along with electrons. A gradient is created that is referred to as the proton-motive force • Now this H+ has the capacity to do work

  22. The electron transport chain made no ATP directly, but it did ease the fall of electrons from food to oxygen • So now, by chemiosmosis, it will couple this electron transport and energy release to ATP Synthase • ATP Synthase is an enzyme that catalyses ATP from ADP and an inorganic phosphate • Each NADH produces 3 ATP • Each FADH produces 2 ATP

  23. To summarize, for each glucose molecule… • Glycolysis makes 2 NET ATP and 2 NADH and • 2 pyruvate 2 acetyl CoA = 2 NADH • Krebs Cycle: 6 NADH, 2 FADH2, 2 ATP • Since each NADH produces 3 ATP during oxidative phosphorylation and each FADH2 produces 2 ATP…how many ATP total?

  24. Wait…but what if there is no oxygen? • What will be affected? Well now there is no electron acceptor to accept electrons at the end of the ETC. NADH will accumulate. Once all NAD+ has been made to NADH, Krebs and glycolysis will eventually stop. • We have to free NAD+ to allow glycolysis to continue! We must release some NAD+ for use by glycolysis

  25. FERMENTATION(Aanerobic Pathway) • Alcoholic : • Yeast & other microorganisms use this to produce alcohol & CO2 as wastes. • Beer is a beverage made by alcoholic fermentation 2 TYPES:Alcoholic & Lactic Acid

  26. Alcoholic Fermentation • Commonly done by yeast in an anaerobic environment. • 1) Glycolysis is done as normal. And then, to regenerate the NAD+… • 2) Pyruvate  acetaldehyde • 3) Acetaldehyde ethanol…the energy in NADH is used to drive this reaction and this will release NAD+. For each acetaldehyde, 1 ethanol is made and 1 NAD+ is produced. • Now we have made 2 ATP from glyocolysis for each 2 converted pyruvate

  27. Or…we can do Lactic Acid Fermentation (Aanerobic Pathway) • Lactic Acid: • Exercise causes the body needs more oxygen for respiration to make more ATP • Body resorts to lactic acid fermentation to make ATP • Lactic Acid is also produced causing burning sensation in muscles

  28. Lactic Acid Fermentation • Commonly done by: Muscle cells during oxygen debt. • Same thing as before: - do glycolysis - but then to regenerate NAD+, a byproduct called lactate is made instead of acetylaldehydeethanol.

  29. Diagram Assignment • You will diagram the major pathways to respiration in color in a way that is understandable to you. Use websites and the book to help you form diagrams for each section of respiration. • It must be in color, complete, and have words on it to describe what is happening in the process for full credit. • Also must have an input/output chart by each stage: glycolysis, krebs, + ETC

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