Cellular Respiration

1. Cellular Respiration

2. I.Cellular Respiration is the main metabolic pathway by which energy is released from food A. This is the primary pathway for Heterotrophs (those that cannot make their own food) B. Breakdown of carbohydrates, proteins, fats (chemical energy) releases ATP II. 2 Main Energy Releasing Pathways A. Aerobic Respiration B. AnaerobicRespiration

3. What is ATP? • ATP is the energy currency • of the cell. • ATP is comprised of a sugar, a nitrogenous base, and 3 phosphate groups, which means that it is a nucleotide • Removal of a phosphate from ATP releases • energy and activates another molecule to do work

4. II. 2 Main Energy Releasing Pathways A. Aerobic Respiration B. AnaerobicRespiration

5. A. Overall Reaction for Aerobic Respiration In the presence of oxygen Glucose Oxygen Carbon dioxide Water Energy Most of the ATP is formed with the help of coenzymes which accept/carry/donate electrons through a series of oxidation-reduction reactions: FAD (oxidized) FADH2 (reduced) NAD+ (oxidized) NADH (reduced)

6. During cellular respiration, hydrogen and its bonding electrons change partners • Hydrogen and its electrons go from sugar to NAD+/FAD to oxygen, forming water Oxidation [Glucose loses electrons (and hydrogens)] Glucose Oxygen Carbon dioxide Water Reduction [Oxygen gains electrons (and hydrogens)]

7. Why does electron transfer to oxygen release energy? • When electrons move from glucose to oxygen, it is as though they were falling • This “fall” of electrons releases energy during cellular respiration Release of heat energy Figure 6.5

8. All of the reactions involved in aerobic cellular respiration can be grouped into three main stages • Glycolysis • The Krebs cycle • Electron transport

9. A Road Map for Cellular Respiration Cytosol Mitochondrion High-energy electrons carried mainly by NADH High-energy electrons carried by NADH Glycolysis Krebs Cycle 2 Pyruvic acid Electron Transport Glucose Figure 6.7

10. Overview of Aerobic Respiration Glucose Glycolysis 2 ATP Pyruvate/ NADH Cytoplasm mitochondria Krebs Cycle 2 ATP 32-34 ATP Electron Transport System

11. Both Aerobic and Anaerobic pathways begin with: “sugar-breaking” - one molecule of glucose is split into two molecules of pyruvate Glycolysis 2 ATP Glucose 2 Pyruvate (6 carbons) NADH 4 ATP (3 carbons each) Net 2 ATP

12. The Krebs cycle completes the breakdown of sugar A. 2 Pyruvate molecules from glycolysis enter the matrix of the mitochondria. • With the help of coenzymes (NAD+/FAD), one carbon atom • is removed from pyruvate and released as CO2. • The resulting 2-carbon molecule is ready to enter the cycle C. NAD+ and FAD pick up electrons and H+ (are reduced) NADH and FADH2 D. A net of 2 ATP are produced E. Intermediates are regenerated to keep the cycle going

13. The Krebs cycle completes the breakdown of sugar • The Krebs cycle extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2 • The cycle uses some of this energy to make ATP • The cycle also forms NADH and FADH2

14. The Electron Transport Chain A. Electrons from NADH and FADH2 are passed along from one molecule to the next in the chain. B. At the end of the chain, oxygen accepts electrons and combines with H+ to produce water. C. Special molecules pump hydrogen ions (H+) across the inner membrane, creating a concentration gradient Chemiosmosis D. H+ move back down the concentration gradient through specialized membrane proteins called ATP synthases this drives ATP production E. A net of 32-34 ATP are produced.

15. Inside the mitochondria... The membranes of the mitochondria are very important to the process of cellular respiration. Intermembrane space Matrix christae

16. Protein complex Electron carrier Inner mitochondrial membrane Electron flow ATP synthase Electron transport chain Figure 6.12

17. IV. Summary of Aerobic Respiration (In the presence of Oxygen) A. Preceded by glycolysis in the cytoplasm B. 2 Stages after glycolysis occur in the MITOCHONDRIA 1. Krebs Cycle 2. Electron Transport Chain C. Net energy yield~ 36-38 ATP

18. III. Anaerobic Respiration (In the absence of oxygen) A. Takes place entirely in the CYTOPLASM B. Begins with glycolysis C. Uses Fermentation pathways 1. Lactate fermentation 2. Alcoholic fermentation D. Net energy yield= 2 ATP

19. Fermentation Glucose Lactate (bacteria) Glycolysis 2 ATP Pyruvate Fermentation Ethanol + CO2 (yeast, fungi) NADH

20. V. Aerobic vs. Anaerobic Respiration Anaerobic Aerobic # Steps (incl. Glycolysis): Location: Net Energy yield: 2 3 Cytoplasm Cytoplasm/Mitochondria 2 ATP ~36-38 ATP

21. Study Objectives 1. For which type of organism is cellular respiration the main metabolic pathway? 2. When are aerobic and anaerobic pathways used? 3. Write the overall reaction for aerobic respiration. 4. Describe the structure of ATP and how it provides a source of energy for the cell. 5. Explain what happens in glycolysis. How many net ATP are produced? 6. What are the products of lactate and alcoholic fermentation? 7. What are the stages of aerobic respiration after glycolysis? 8. Describe the structure of the mitochondria and explain how this is important to the production of ATP. 9. Describe the principle steps of the Krebs cycle. Where in the mitochondria does the cycle take place? How many ATP are produced? What other compounds are released as a result of the cycle? 10. Describe the principle steps of the electron transport chain. Where in the mitochondria is the chain located? How many ATP are produced? What is formed as a result of the ETC? 11. Explain the roles of NAD+ and FAD in the ETC. 12. What is the final electron acceptor in the ETC? 13. Explain how ATP is synthesized by chemiosmosis.