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METABOLISM
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  1. METABOLISM Historical Perspective Definitions Methods Factors affecting Metabolic Rate

  2. Antoine Lavoisier, 1773 • heat produced by an animal is proportional to O2 consumed and CO2 produced • so…“animal heat” is a byproduct of chemical reactions (metabolism)

  3. Maintenance, growth, reproduction, activity Energy Food/fuel is oxidized to form ATP Metabolism= sum of all biological transformations of energy and matter Metabolic Rate= Total energy metabolized by an organism per unit time

  4. Maintenance, growth, reproduction, activity Energy Fuel + O2 CO2 + H2O + ATP + heat Food/fuel is oxidized to form ATP Aerobic metabolism:

  5. Metabolic rate (MR, or E) = energy metabolism/time What does MR tell us? Overall rate of all physiological activities Resource needs Rate of production of new tissue

  6. Aerobic metabolism: Fuel + O2 CO2 + H2O + ATP + heat * Indirect measures Direct measures How can we measure MR?

  7. Lavoisier & Laplace 79.9 cal melts 1 g ice (335 Joules) 1. Direct measure of heat production = “direct calorimetry”

  8. Aerobic metabolism: Fuel + O2 CO2 + H2O + ATP + heat * Indirect measures Direct measures How can we measure MR?

  9. food intake (fuel) O2 consumption CO2 production metabolic water Fuel + 6O2 6CO2 + 6H2O + 2820 kJ 2. Indirect measure of MR X Complete oxidation of 1 mol glucose: (C6H12O6) • Amount of energy ingested, O2 consumed, or CO2 produced is directly related to amount of heat produced

  10. E = 0.06 L O2 /hr Measuring O2 consumption: Closed system respirometry: Volume = 1 L Initial O2 = 21% 1000 mls 210 mls O2 Final O2 = 15% 150 mls O2 (1 hour)

  11. Measuring O2 consumption: Open system respirometry (flow through): Constantly measure O2 consumption

  12. Respirometry: Open and Closed Can be used to measure BOTH: Oxygen consumption Carbon Dioxide Production

  13. food intake (fuel) O2 consumption CO2 production metabolic water Fuel + 6O2 6CO2 + 6H2O + 2820 kJ 2. Indirect measure of MR X Complete oxidation of 1 mol glucose: (C6H12O6) • Amount of energy ingested, O2 consumed, or CO2 produced is directly related to amount of heat produced • BUT, heat production varies with foodstuff being oxidized…

  14. BUT, heat production varies with foodstuff being oxidized… Relatively constant, but not exact… HEAT PRODUCTION (KJ) Per gram of food Per liter of O2 consumed Per liter of CO2 produced 21.1 17.1 21.1 carbohydrates 19.8 38.9 27.9 lipids 18.7 17.6 23.3 Proteins (urea)

  15. Heat produced per liter of O2 consumed (KJ/L) 21.1 carbohydrates 19.8 lipids 18.7 Proteins (urea) E = 0.06 L O2 /hr To convert to heat production: Use appropriate conversion factor (on left) - possible if you know food source -OR- 2) Use a “representative” conversion factor - 20.2 KJ/L Thre is a more complicated method, but you need to measure both O2 consumption and CO2 production (rare)

  16. How does energy use compare between lab and field? • Values of MR in field are 3X higher than in lab!! Why? Field metabolic rate, (“FMR”) accounts for activity levels!

  17. 18O O H 3H H H (Water) (Doubly-labeled water) How can we measure FMR? Doubly labeled water: • dual isotope technique • can use with free-ranging terrestrial animals • no equipment attached to animal • measures CO2 production

  18. Inject into animal Doubly-labeled water measure the “washout” rates of 3H and 18O 18O H 3H • 3Hlost as body water (urination, sweating, breathing…) • 18Ois lost as water and CO2 **Loss rate for 18O is steeper than for 3H

  19. Initial sample 3H isotope in body Final sample 18O time Doubly-labeled water Convert to estimates of CO2 production…

  20. 3H Initial sample Final sample isotope in body 18O time Doubly-labeled water • inject a known quantity into animal • let equilibrate, take blood sample • release animal • recapture, take 2nd blood sample 3H : 18O

  21. 18O H 3H Doubly-labeled water Is it accurate? • Predicts CO2 production w/in 3-8% Limitations? • cost of analysis • radioisotope use in field

  22. 1. Activity What factors affect an animal’s metabolic rate?

  23. Humans: 30% 1.4 kJ meal 5.6 kJ meal What factors affect an animal’s metabolic rate? 2. Digestion: “specific dynamic action” = MR increase after a meal • Amount • Type Why?

  24. What factors affect an animal’s metabolic rate? 2. Digestion: “specific dynamic effect” = MR increase after a meal 3. Starvation Metabolic rate drops Why might this be adaptive?

  25. Golden-mantled ground squirrels: What factors affect an animal’s metabolic rate? 4. Reproductive Status • Humans:MR increases 30% near term -growth of fetus -fetal metabolic requirements -growth of mammary tissue - lactation takes up 1/3 of yearly energy budget!

  26. 5. Hibernation, Estivation, Torpor What factors affect an animal’s metabolic rate? Many animals lower MR well below resting levels

  27. Relatively high MR Relatively low MR 6. Endothermy vs. Ectothermy

  28. 6. Endothermy vs. Ectothermy • physiological correlates of huge MR difference Higher SA/V in lungs; complex, efficient heart Mitochondrial membrane SA ~4-5X bigger Greater enzyme activity

  29. 6. Endothermy vs. Ectothermy

  30. What does measuring O2 consumption tell us? Endotherms: Ectotherms: • basic metabolism • basic metabolism • thermoregulation • digestion • digestion • activity • activity • reproduction/growth • reproduction/growth “Basal MR” “Standard MR”

  31. endotherms ?? MR BMR temperature 7. Temperature affects MR Basal Metabolic Rate: Animal must be: “tnz” -in TNZ -resting -fasting Thermoneutral zone = range of temps within which MR is unaffected by temp change

  32. ectotherms MR temperature 7. Temperature affects MR “Standard Metabolic Rate” Animal must be: SMR -fasting -resting * SMR is specific to body temp

  33. ectotherms endotherms MR MR BMR temperature temperature 7. Temperature affects MR “tnz” SMR -in TNZ -resting -fasting -fasting -resting -temperature specific BMR: SMR:

  34. Metabolic Rate Summary • What is MR and how can you measure it? • Direct Colorimetry (heat production) • Food Consumption • Oxygen Consumption • Carbon Dioxide Production • Field metabolic rate • Factors affecting metabolic rate: • Activity • Digestion • Starvation • Reproductive Status • Hibernation, Estivation, Torpor • Endothermy vs. Ectothermy • Temperature

  35. METABOLISM Historical Perspective Definitions Methods Factors affecting Metabolic Rate

  36. BUT, heat production varies with foodstuff being oxidized… HEAT PRODUCTION (KJ) Per gram of food Per liter of O2 consumed Per liter of CO2 produced RQ 21.1 17.1 21.1 carbohydrates 1.0 19.8 38.9 27.9 0.7 lipids 18.7 17.6 23.3 0.8 Proteins (urea) “Respiratory Quotient” = Rate of CO2 production Rate of O2 production What if you aren’t sure what animal ate?