Chapter 9 Cell Respiration: Harvesting Chemical Energy

1. Chapter 9Cell Respiration: Harvesting Chemical Energy

2. You will be able to: • Describe the sequence of events & products formed in cellular respiration • Name the location and the products of: • each stage of Glycolysis • the Citric Acid cycle • the Electron Transport Chain • Compare and contrast: • aerobic respiration • anaerobic respiration • fermentation

3. Cellular respiration • Aerobic respiration • Requires molecular oxygen • Includes redox reactions -Anaerobic respiration *Fermentation *Does not require oxygen All are exergonic (occur spontaneously) Use a lot of coupled reactions

4. Takes place in the cytosol: • Glycolysis • Four stages of aerobic respiration Takes place in the mitochondrion: 2. Formation of acetyl CoA 3.Citric acid cycle (Kreb’s Cycle) 4. Electron transport chain / chemiosmosis (electrical-diffusion)

5. Four stages of aerobic respiration Note location of each stage & amount of ATP formed Product of one stage becomes reactant of next stage

6. Reaction Types in Cellular Respiration 1. Dehydrogenation - Hydrogens transferred to a coenzyme. 2. Decarboxylations - Carboxyl groups (COO-) removed from substrates as carbon dioxide (CO2). 3. Preparation reactions - Molecules are rearranged in preparation for dehydrogenation or decarboxylation.

7. Stage #1 • Glycolysis: • Glyco = sugar • Lysis = to split • One 6 C glucose split into • two 3 C pyruvic acids • Substrate Phosphorylation • of glucose occurs to make the reactions exergonic • This occurs in the Cytosol • of the cell

8. How Free-Energy Currency Works Coupled reactions: Example • the phosphorylation of glycerol, and • the de-phosphorylation of ATP (ATP = the free-energy-currency molecule).   1.     Glycerol + HPO42- (Glycerol-3-Phosphate)2- + H2O DGo = +9.2 kJ (nonspontaneous)   2.    ATP4- + H2O  ADP3- + HPO42- + H+ DGo= -30.5 kJ (spontaneous) Coupled reaction:       Glycerol + ATP4- (Glycerol-3-Phosphate)2- + ADP3- + H+ DGo= -21.3 kJ (spontaneous!)

9. Glycolysis: • essentially the starting point of all respiration • “Sugar splitting” • Does not require oxygen (anaerobic or aerobic) • Divided into two major phases: • Energy investment phase • Energy capture phase • Each glucose molecule produces net yield of two NADH molecules and two ATP molecules

10. Glycolysis: • energy • investment • Phase in gross detail • Phosphorylation Isomer: 2nd C sticking up ATP kick start Glucose turned into Fructose-1,6-bisphosphate this turns into 2 glyceraldehyde-3-phosphate (called G3P) P group on both ends Two 3 C long molecules form Both have a phosphate

11. The two • glyceraldehyde-3-phosphates • are eventually turned into • two pyruvates • The endproducts of glycolysis include: • 2 molecules of pyruvate • 2 molecules of NADH • - Energy carrier • and 2ATP molecules • net gain(4 made / 2 used) • Glycolysis:E capture phase

12. What happens to the end products of Glycolysis in the cytosol? If O2 is present for the completion of cell respiration, then pyruvic acid undergoes a transition reaction, preparing it for the Kreb's Cycle: 2 Pyruvic Acid  2 Acetyl coenzyme A + CO2 More CO2 being made!

13. Formation of acetyl CoA • Catalyzed by enzyme pyruvate dehydrogenase • First the carboxyl group is split off as carbon dioxide • Remaining two-carbon fragment is oxidized and electrons transferred to NAD+ making NADH • Remember “OIL RIG?” • Finally, the oxidized two-carbon acetyl group is attached to coenzyme A • Creates acetyl CoA

14. Formationof acetyl CoA: • CO2 is formed • as a waste product The ~ represents a strained bond (called “high energy” bond)

15. Citric acid cycle • For every glucose, two acetyl groups enter the citric acid cycle(Krebs cycle) • Each two-carbon acetyl group combines with a 4-carbon compound (oxaloacetate) • Eventually 2 CO2 molecules are removed • Energy captured as 1 ATP, 3 NADH, and 1 FADH2 for each acetyl group

16. Citric acid cycle: • complete oxidation of one glucose molecule requires 2 turns of the Kreb's Cycle • Because each molecule of glucose produces twopyruvates

17. Detail of • The Krebs cycle • (a.k.a. citric acid cycle) • Net production of (6) NADH, • (2) FADH2, • (2) ATP and • release of • (4) CO2 molecules So that’s where the carbon dioxide comes from!

18. Series of electron carriers • Electron transport chain • Each carrier exists in oxidized • or reduced form • High energy electrons pass down the • electron transport chain in • a series of redox reactions • They lose energy as they pass along the chain Electron transport chain movie

19. 6 NADH & 2 FADH2 transport glucose energy to E.T.C. A series of special protein trans-membrane molecules, cytochrome molecules, a speciallipid (ubiquinone) all embedded in the inner membrane of the mitochondria. electrons delivered by carrier molecules (NADH and FADH2) begin at high energy levels.

20. Electron transport chain inner membrane is up to 75% protein by mass - allows only O2, CO2 and H20 to freely pass

21. As the electrons are passed from one cytochrome to another, they lose energy which is indirectly used to make ATP As electrons reach the end of the cytochrome chain, they’re picked up and removed by O2, which reacts with left over hydrogen ions, forming water. This is the water that you sweat, excrete, & breath out.

22. Accumulationof protons • Within the • inter-membranespace

23. How is ATP made from the E.T.C.? • Energy released at each step of electron hand-off, used to pump H+ ionsoutside of inner mitochondrial membrane • Establishes a strong concentration gradient. • H+ ions then return thru the membrane by special protein channels via chemiosmosis (electrical diffusion). • Energy released is used to produce lots of ATPby Oxidative Phosphorylation

24. Electron transport and chemiosmosis: • e- energy used to pump H+ ions • out of the matrix Note the last protein: ATP synthase

25. World’s smallest rotary motor: ATP synthase is the transmembrane protein enzyme that taps H+ ionenergy to perform phosphorylation on ADP creating ATP

26. Energyyield fromcompleteoxidation ofglucose • (e- loss) via aerobicrespiration anaerobic fermentation results in just 2 ATP

27. What about food other than sugar? How is it processed? • Many organisms depend on nutrients other than glucose • Products of protein and lipidcatabolism enter same metabolic pathways as glucose • Amino acids are de-aminated (NH2) so proteins are bit tougher to process & produce toxic ammonia (NH3)

28. Processing other • macromolecules • from our food • for energy:catabolic pathways for carbohydrates,proteins, and fats

29. Catabolic pathway for Protein • Protein hydrolyzed makes individual amino acids. • A.A.s can be broken down by having amine group stripped (de-amination) • Remaining carbons can enter Glycolysis, or hook to coenzyme A, or enter directly into Krebs cycle and on to the ETC. • Waste products are urea (ammonia) molecules that are excreted in urine.

30. Catabolism of lipids • Lipids busted up into glycerol (3C), can be converted to pyruvate (3C) in glycolysis • Fatty acidscan be broken down into two carbon molecule pieces that enter the Krebs cycle and then go on to the ETC. • The other two waste products are CO2 and water • 3 molecules of fatty acids (18 C atoms each) yields about 441 ATP molecules!

31. Mitochondrial production of heat: Brown Fat • extraordinary # of mitochondria, involved in heat generation • important to neonates, small mammals in cold environments, and hibernating animals mitochondrial uncoupling protein: thermogenin mitochondria uncouple from oxidative phosphorylation ETC system generates heat instead of ATP

32. Anaerobic respiration • Electrons transferred from fuel molecules • to an electron transport chain (ETC) • No Krebs cycle • Final electron acceptor is an • inorganic substance • Anaerobic respirationvsfermentation • Fermentation • Anaerobic process that does not use an • electron transport chain • Organic compounds are reduced • Substrate level phosphorylation only

33. Anaerobic respiration • Prokaryotes that live in waterlogged soil, stagnant ponds, or animal intestines have to do anaerobic respiration. • No O2 available to pick up used e- and H+ ions. • They still use an ETC but with fewer energy carrier molecules (no Krebs cycle to oxidize them) • must use a different electron acceptor (not oxygen). • Use inorganic anions: nitrate (NO31-) & sulfate (SO42-) - are easily reduced • Small yield of ATP but utilizes difficult environments

34. Fermentation: Yeasts (single-celled eukaryotic fungi) and some bacteria can also do a different type of anaerobic respiration when O2isn’t readily available. Not very efficient: it’s just glycolysis with an extra bit added to recycle the NADH back to NAD+.

35. Alcoholic fermentation Yeast excretions! Yum! Yum! Yeasts are facultative anaerobes: they switch to fermentation when O2 levels are low.

36. This recycles NAD+ to keep glycolysis working • In alcoholic fermentation, 3 C pyruvic acid is converted to CO2 and ethanol (C2H5OH) Ethanol is the oxidizing agent helping NADH get oxidized back to NAD+. 2 Ethanol 2 Pyruvicacid released Glucose GLYCOLYSIS Pyruvic acid is decarboxylated forming CO2 and ethanol NADH molecules oxidized back into NAD+.

37. Alcoholic fermentation Yeast is allowed to do anaerobic alcohol fermentation to produce ethyl alcohol. Above ~17% alcohol content the yeast die off.

38. As in alcoholic fermentation, NADH is recycledby oxidation back toNAD+ • Lactic acid fermentation is used to make cheese, yogurt, kefir, sauerkraut, pickles, and poi • In lactic acid fermentation, pyruvic acid is converted to lactic acid 2 Lactic acid 2 Pyruvicacid Glucose GLYCOLYSIS

39. Skeletal muscle tissue is composed of 2 general types of muscle fibers: fast-twitch and slow-twitch • Slow -twitch muscle fibers used for: • - steady, low-intensity, repetitive contraction. • Do not tire easily – used for endurance. • Used for low-intensity, high-endurance activities: • - long distance running.

40. Fast-twitch muscle fibers used for: • - heavy work, strength and power.  • Contract quickly, providing short bursts of energy. • High-intensity, low-endurance activities: • - sprinting, weightlifting, or shot-putting. • Fast-twitch muscle fibers become exhausted quickly.

41. Lactic acid fermentation running from danger, pushing beyond body’s ability to provide O2 to muscles – must switch to anaerobic fermentation

42. CH3CHOHCOOH During Fast-twitch muscular exercise: • Increase O2 supply by dilating blood vessels in muscles – increases blood flow • Running from danger pushes beyond bodies’ ability to provide O2 • Muscles kick over to anaerobic fermentation. • Muscles continue to break down glucose to liberate some energy for a short time • This partial breakdown produces lactic acid • When lactic acid reaches certain levels in the muscles and blood - fatigue occurs

43. Oxygen debt: waste not, want not! Why do you keep breathing hard after you stop exercising?

44. Huffing & puffing after exercise helps repay the “oxygen debt” • Break down the lactic acid • get the rest of the energy out of the molecules • Once adequate O2 is available, lactic acid must be catabolized • Broken down into CO2 and H2O • Pay back any oxygen that has been borrowed from hemoglobin, myoglobin, air in the lungs, and body fluids • Hard breathing and sufficient discomfort stops muscle activity until homeostasis is restored

45. Comparison of aerobic respiration, anaerobic respiration, and fermentation. • Quick review in your textbook • Compare: • Amounts of ATP produced • Does chemiosmosis / oxidative phosphorylation occur? • Is an ETC part of the process? • What are the reduced end products?