NOTES – Cell Energy Part 3 (Cellular Respiration)

1. NOTES – Cell Energy Part 3 (Cellular Respiration)

2. Cell Energy Review • Cell Energy Part 1 – ATP • ATP is the “energy currency” of the cell • Cells must regenerate ATP from ADP and P to keep working • A constant input of energy (food) is required to power the ATP cycle • Cell Energy Part 2 – Photosynthesis • The source of almost all food molecules • Light energy is converted into chemical energy and stored in the bonds of high-energy molecules • These molecules are used to power the ATP cycle and are used as skeletons to build other molecules necessary for life

3. Metabolism – The Chemical Reactions of an Organism • Metabolism – the set of chemical reactions that happen in an organism to maintain life • Allow organisms to grow/reproduce, maintain structures, respond to environment • Organized into pathways, where one chemical is transformed through a series of steps into another chemical • Two categories: catabolism and anabolism

4. Metabolism – The Chemical Reactions of an Organism • Catabolism– metabolic reactions that release energy by breaking down complex molecules into simpler compounds • Ex - Cells break down glucose to power the ATP cycle (cell respiration) • Anabolism – metabolic reactions that store energy by building simpler compounds into more complex molecules • Ex - Photosynthesis

5. Glucose-Glycogen Metabolism

6. How do cells use food molecules, such as glucose, to produce ATP? • Glycolysis – process where glucose is broken down into 2 pyruvic acid molecules • Takes place in cytoplasm of all cells • Requires glucose, 2 ATP, and NAD+ • Produces 2 pyruvic acid, 4 ATP, and 2 NADH • Glucose + 2 ATP + NAD+  2 pyruvic acid + 4 ATP + 2 NADH • Net gain of 2 ATP molecules

7. Glycolysis – What happens? • 4 e- are removed from glucose and transferred to 2NAD+ which become 2 NADH • NAD+ must be present to accept e- from glucose, otherwise glycolysis cannot take place • Small overall energy yield (2 ATP), but extremely fast process • After a few seconds, all of a cell’s available NAD+ is used up

8. What happens when there is no more NAD+? • Cells need a way to convert NADH back into NAD+ • How they do this depends on the amount of oxygen present in the cell • Insufficient oxygen = fermentation • Plentiful oxygen = aerobic respiration

9. Fermentation • Fermentation – process where e- from NADH are passed back to pyruvic acid molecules, producing NAD+ • Keeps glycolysis going • Anaerobic process – does not require oxygen • Pyruvic acid molecules are changed into new products • Most cells perform some type of fermentation

10. Alcoholic Fermentation – process where pyruvic acid accepts e- from NADH producing ethyl alcohol, CO2, and NAD+ pyruvic acid + NADH  ethyl alcohol + CO2 + NAD+ Performed by yeast, plants, some bacteria Used to produce alcohol in wine, beer, etc. Used to make bread rise 2 Common Types of Fermentation

12. Honey Wheat Sandwich Bread • The holes in the bread are made by bubbles of CO2 in the dough • The alcohol produced by the yeast boils away in the oven

13. Rustic Bread

14. Italian Bread

15. French Bread

16. Ciabatta Bread

17. Plain and Sesame Bagels

18. Cinnamon Raisin Bagels

19. Marble Rye Bread

20. Casatiello Bread

21. Sourdough Bread

22. Pane Siciliano (Sicilian Bread)

23. Oatmeal Bread

24. Pizza

25. Pita Bread

26. Soft Pretzels

27. Bretzel (Bavarian Pretzel) Rolls

28. Hard Rolls (Kaiser Rolls)

29. Lactic Acid Fermentation – process where pyruvic acid accepts e- from NADH producing lactic acid and NAD+ pyruvic acid + NADH  lactic acid + NAD+ Performed by animals, some bacteria Used to produce cheese, sour cream, yogurt Responsible for quick bursts of energy in animals (Ex. Sprinting) 2 Common Types of Fermentation

30. Different Types of Fermentation

31. Lactic Acid Fermentation and Exercise • Low oxygen = body converts pyruvic acid into lactic acid = continued glycolysis • After 1 to 3 minutes, lactic acid concentration in muscles is high • High lactic acid = burning sensation in muscles & less glucose breakdown • You stop = muscle damage is prevented • Rest + oxygen = lactic acid  pyruvic acid

32. Remember… • The goal of fermentation is to generate NAD+ to keep glycolysis going in low oxygen conditions • The e- from NADH are passed back to pyruvic acid molecules, generating different products and NAD+ • If there is plenty of oxygen available, in most cells a different process occurs

39. Cellular Respiration – Overview • After glycolysis about 90% of the chemical energy available in glucose is still unused • The energy is locked up in the pyruvic acid molecules • In the presence of plentiful oxygen, most cells can break down pyruvic acid molecules further, generating much more ATP

40. Cellular Respiration • Cellular Respiration – process that releases energy by breaking down food molecules (glucose) in the presence of oxygen • 6 O2 + C6H12O6 6 CO2 + 6 H2O + 36 ATP • Aerobic process – requires oxygen • In eukaryotic cells, respiration takes place in mitochondria • In some prokaryotic cells, the entire cell functions like a single mitochondrion, allowing respiration to be carried out

41. Cell Respiration – What happens? Cell Respiration is a 3-Step process: • Glycolysis – begins break down of glucose in cytoplasm into pyruvic acid • Krebs Cycle – breaks down pyruvic acid into CO2, releasing energy (in mitochondria) • Electron Transport Chain – generates ATP in mitochondria using products from the Krebs Cycle

42. Step 1 - Glycolysis

43. Outer membrane – simple phospholipid bilayer Inner membrane – highly folded phospholipid bilayer, site of electron transport chain Matrix – inner portion of mitochondrion, site of Krebs Cycle Structure of Mitochondrion

44. The Krebs Cycle (Citric Acid Cycle) • 2nd stage of cell respiration where pyruvic acid molecules are broken down producing CO2, NADH, FADH2, and ATP • 2 pyruvic acid  6 CO2 + 8 NADH + 2 FADH2 + 2 ATP • NADH & FADH2 carry e- to the final stage of cell respiration • CO2 is a waste product

45. Step 2 – Krebs Cycle

46. The Electron Transport Chain (ETC) • 3rd stage of cell respiration where e- from the Krebs Cycle are used to convert ADP into ATP • e- are passed from NADH and FADH2 to a series of carrier proteins that are embedded in the inner membrane of a mitochondrion • As the e- pass from one protein to the next, H+ ions are pulled from the matrix into the intermembrane space of the mitochondrion • e- flow back into the matrix through ATP sythase proteins, which use the energy to convert ADP into ATP

47. Using e- to make ATP

48. What happens to the electrons? • As e-reach the end of the chain, they must go somewhere, or else the chain cannot accept new e-from the Krebs Cycle • Oxygen molecules accept the e-, and immediately bond H+ ions, forming H2O molecules • As long as there is plentiful oxygen, NADH is continually converted to NAD+ by the ETC, allowing glycolysis to continue • If oxygen is not brought in quickly enough, the chain slows down, NAD+ is quickly used up, and fermentation begins

49. Step 3 – Electron Transport Chain

50. How much energy does cellular respiration provide? • Overall ~ 36 ATP • Glycolysis = 2 ATP • Krebs Cycle = 2 ATP • ETC = 34 ATP • 2 ATP are used up transporting pyruvic acid into mitochondria • 36 ATP represents about 40% of the energy released from glucose, the other 60% is converted to heat energy