Cellular Respiration

1. Cellular Respiration Textbook Chapter 8 Review Book Topic 2

2. Cellular Respiration • Living things rely on the chemical energy stored in the food they digest • Energy (e-) released from the breakdown of glucose is used to combine ADP + Pi to form ATP • Occurs in autotrophs and heterotrophs in the mitochondria

4. There are two types of cellular respiration • Aerobic • Anaerobic • First step is the same for all organisms • Glycolysis

5. Anaerobic Respiration • Does not require oxygen (O2) • Cell receives very little of the chemical energy in glucose • Ex. Yeast, bacteria • Only carries on glycolysis and fermentation steps of cellular respiration

6. Aerobic Respiration • Requires oxygen (O2) from the atmosphere or from the water in which it is dissolved • Glucose is completely broken down into carbon dioxide and water • Allows the maximum amount of energy to be removed from glucose • Ex. Eukaryotic organisms (humans, plants, etc.)

7. Glycolysis • Splitting of glucose (6-carbons) into two pyruvic acid molecules (3-carbons) • Occurs in the cytoplasm of the cell

9. Begins with phosphorylation • Two phosphates bond to one glucose molecule using energy from the breakdown of ATP • Glucose is split in half to form PGAL (phosphoglyceraldehyde) • PGAL loses electrons to become pyruvic acid

11. For each pyruvic acid molecule produced • 2 ATP molecules are formed • NAD+ is converted to NADH • Net energy output of glycolysis • 4 ATP molecules produced for every glucose molecule • 2 NADH (used later when O2 is present to form additional energy)

12. Fermentation(Anaerobic) • In anaerobic respiration, all energy obtained by the cell is from the process of glycolysis • No additional ATP is produced by any other reactions carried out by the cell

13. Pyruvic acid is changed into other compounds • Ex. Yeast - ethyl alcohol and carbon dioxide • CO2 causes bread to rise • Ethyl alcohol is used to make wine, beer, liquor • Ex. Bacteria – lactic acid

14. Pyruvic Acid Breakdown(Aerobic) • Occurs within the mitochondria of the cell • Reactions occur on the inside or the surface of the inner membrane

15. Pyruvic acid breaks down into • Carbon dioxide • NADH • Acetyl CoA • 2-carbon compound combined with coenzyme A (CoA) • Acetyl CoA enters the Krebs cycle

16. Krebs Cycle(Aerobic) • Each turn of the Krebs cycle: • Requires 1 molecule of acetyl CoA • Yields 2 molecules of carbon dioxide, 3 molecules of NADH, 1 molecule of FADH2 • Produces only 1 ATP molecule

17. For each glucose molecule the Krebs cycle turns twice • Overall net output of 2 ATP • Almost all the chemical energy removed from the pyruvic acid is carried by the electrons produced

19. All remaining energy released by the breakdown of glucose is carried by the electrons in NADH and FADH2 • Carried out by the electron transport chain to release energy from NADH and FADH2 • Energy (e-) is used to pump H+ ions across the mitochondrial membrane (just like in photosynthesis)

20. Most of the energy in aerobic respiration is produced by chemiosmosis • H+ go from high to low concentration by passing through ATP synthase in mitochondrial membrane • Energy produced from the movement of H+ allows ADP + P  ATP

21. Oxygen atom combines with each pair of H+ to form water • Water is used by the cell or excreted • 32 ATP molecules are produced by the electron transport chain for each molecule of glucose

22. Aerobic Respiration Summary • Produces a total of 36 ATP molecules from each molecule of glucose • 2 ATP – glycolysis • 2 ATP – Krebs cycle • 32 ATP – electron transport chain • Net reaction: C6H12O6 + 6 H2O + 6 O2 6 CO2 + 12 H2O + 36 ATP

24. Efficiency of Cellular Respiration • Anaerobic respiration only produces 2 ATP • Very inefficient • Leaves most of the potential energy of the glucose in the end products of fermentation • Meets the needs of many simple organisms (ex. yeast, bacteria)

25. Aerobic respiration yields almost 20 times as much energy per glucose molecule as fermentation does • Efficient • About 45% of the total energy obtainable from the breakdown of glucose is stored as ATP molecules • Ex. automobile engines only convert 25% of the chemical energy of its fuel into useful energy

26. Muscle Fatigue • Some organisms that have the capacity for aerobic respiration can function by anaerobic respiration alone when free oxygen is not available

27. Ex. Muscle cells can function for a short amount of time without oxygen by using the energy obtained from glycolysis alone • During prolonged periods of physical activity, the muscle cells use oxygen faster than it can be supplied (shuts down Krebs cycle) • Muscles then continue to release energy by glycolysis • Pyruvic acid is converted to lactic acid which can build up causing muscle fatigue

28. Respiration of Fats and Proteins • Other organic compounds can be broken down using aerobic respiration to extract energy from proteins and fats • Broken down and converted to compounds that can enter the respiratory pathway at an intermediate point in the glucose breakdown pathway • When fats are used for energy, twice as much ATP is produced as when glucose is used • When proteins are used for energy, the same amount of energy is produced as a carbohydrate (not preferred by the cell)