Section 2.3: Related Pathways

1. Section 2.3: Related Pathways • Carbohydrates are the first nutrients most organisms catabolize for energy. However, when necessary, most organisms can metabolize proteins, lipids and nucleic acids.

3. Protein Catabolism Lipid Catabolism Anaerobic Pathways Related Pathways

4. Protein Catabolism Protein  amino acids  deamination  ammonia (NH3) • The remaining portions of amino acids are converted into various components of glycolysis or Kreb cycle. • Examples: • Leucine  acetyl-CoA • Alanine  pyruvate • Proline  α ketoglutarate

5. Lipid Catabolism • Triaglycerides  glycerol + fatty acids • Glycerol  Glucose (gluconeogenesis) or DHAP then G3P • Fatty acids  β-oxidation (matrix)  acetyl-CoA • Each cleavage uses 1 ATP and produces 1 NADH and 1 FADH2 • Produces more ATP than Glucose (see pg. 118) Concepts in Biochemistry - Interactive Animations

7. Anaerobic Respiration • During oxygen deficient periods, the process of cellular respiration can get backed up. • NADH cannot get recycled back to NAD+ to pick up more electrons. • Organisms have evolved a way to recycle NAD+ and allow glycolysis to continue.

8. Fermentation: ATP from Glucose, without O2 • Many organisms and some cells live without O2, deriving energy from glycolysis and fermentation. Together, these pathways partly oxidize glucose and generate energy-containing products. Fermentation reactions anaerobically oxidize the NADH + H+ produced in glycolysis.

9. Anaerobic Pathways • Required to recycle NADH when oxygen levels are low. • Ethanol Fermentation • NADH passes it H atoms to acetaldehyde (formed when CO2 is removed from pyruvate), this forms ethanol. • NAD+ can be recycled and glycolysis continues. • Lactic Acid Fermenatation • NADH transfers its H atoms to pyruvate forming lactate

10. Figure 7.15 Lactic Acid Fermentation

11. Lactic Acid Fermentation • NADH transfers its hydrogen atoms to pyruvate to form lactate • Lactate can be oxidized back to pyruvate when the strenuous exercise stops • Extra oxygen (oxygen debt) is required to catabolize lactate into CO2 and H2O

12. Figure 7.16 Alcoholic Fermentation

13. Ethanol Fermentation • CO2 is removed from pyruvate to form acetaldehyde • NADH passes its hydrogen atoms to acetaldehyde to form ethanol • Carried out by yeast • Breads, wine, beer, liquor, soy sauce Videos\Fermentation (Anaerobic respiration) Lactic Acid and Ethanol.flv

14. Contrasting Energy Yields • For each molecule of glucose used, fermentation yields 2 molecules of ATP. In contrast, glycolysis operating with pyruvate oxidation, the citric acid cycle, and the respiratory chain yields up to 36.

15. Figure 7.17 – Part 1 Energy Yields

16. Figure 7.17 – Part 2 Energy Yields

17. Metabolic Pathways - Metabolic Mill • Catabolic pathways feed into the respiratory pathways. Polysaccharides are broken down into glucose, which enters glycolysis. Glycerol from fats also enters glycolysis, and acetyl CoA from fatty acid degradation enters the citric acid cycle. Proteins enter glycolysis and the citric acid cycle via amino acids. • Anabolic pathways use intermediate components of respiratory metabolism to synthesize fats, amino acids, and other essential building blocks for cellular structure and function.

18. Figure 7.18 The Metabolic Mill

19. VO2 Max and Lactate Threshold Aerobic fitness • the ability of the heart, lungs, and bloodstream to supply oxygen to the cells of the body during physical activity. VO2 max: • The max.volume of oxygen (mL) that the cells of the body can remove from the bloodstream in one minute/kg of body mass while the body experiences maximal exertion • Typical value: 35 mL/kg/min • Elite athletes: 70 mL/kg/min

20. Videos\VO2 Max Test.flv

21. Lactate Threshold Videos\Lactate Threshold.flv

23. Homework • Prep for Investigation 2.2.1, pp. 128, download worksheet • pp. 124, # 1-13 • Chapter 2 Quiz: Monday October 19th • Prep for Quiz: pp. 133, Self-Quiz • Prep for Quiz: pp. 134, try answering Review questions