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Respiration

Respiration. Biological process whereby the energy stored in carbohydrates from PS is released in a step-wise, controlled manner. Energy released is coupled to the synthesis of ATP. ATP is essential for plant cell maintenance, growth and development. Carbohydrate Conversion. Starch glucose

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Respiration

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  1. Respiration • Biological process whereby the energy stored in carbohydrates from PS is released in a step-wise, controlled manner. • Energy released is coupled to the synthesis of ATP. • ATP is essential for plant cell maintenance, growth and development

  2. Carbohydrate Conversion • Starch glucose • Sucrose + water glucose + fructose

  3. Equation for Aerobic Respiration C6H12O6 + 6O2 + 6H2O 6CO2 + 12H2O + energy (glucose)(ATP) 1 mole glucose 36 ATP

  4. Efficiency of Aerobic Respiration • ADP-P bond releases -7.6 kcal/mol ATP when bond is broken • Theoretical energy yield from burning 1mol glucose in a calorimeter = -686 kcal/mol • Practical yield from burning 1mol of glucose in the cell with oxygen = 36ATP • 36 ATP X -7.6 kcal/mol = -274 kcal/mol glucose • 274/686 kcal/mol X 100 = 40% efficiency

  5. Efficiency of Anaerobic Respiration • ADP-P bond releases -7.6 kcal/mol ATP when bond is broken • Theoretical energy yield from burning 1mol glucose in a calorimeter = -686 kcal/mol • Practical yield from burning 1mol of glucose in the cell without oxygen = 2 ATP • 2 ATP X -7.6 kcal/mol = -15.2 kcal/mol glucose • 15.2/686 kcal/mol X 100 = 2.2% efficiency

  6. 3 Stages of Respiration • Glycolysis • TCA Cycle • Electron Transport Chain

  7. Glycolysis • Occurs in all living organisms • Only stage which can occur without oxygen • Oldest stage of respiration • operated for billions of years in anaerobic organisms • Converts glucose to 2 pyruvates in cytosol • with O2 goes on to TCA cycle • without O2 pyruvate is converted to lactate or ethanol (fermentation) • Yields 2ATP/mole glucose in the absence of O2

  8. Glycolysis Glucose (6C) 2 Pyruvate (3C) CO2 -O2 -O2 +O2 Ethanol Lactate TCA Cycle

  9. TCA cycle

  10. Electron Transport System NADH and FADH2 e- H+ ATP e- H+ 4e- + 4H++ O22H2O cyt. oxidase

  11. Chemiosmotic model H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Ion concentration difference represents a source of free energy

  12. Chemiosmotic model H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ The energy represented by the H+ gradient is converted to a chemical form (ATP) via the ATP synthase

  13. 3 Stages of Respiration • Glycolysis • cytoplasm • with or without oxygen present • breaks glucose (6C) into 2 pyruvates (3C) • TCA Cycle • mitochondrial matrix • only if oxygen present • converts pyruvate via acetyl CoA into CO2; generates NADH and FADH2 • Electron Transport Chain • mitochondrial membranes = cristae • transfers electrons from NADH and FADH2 to reduce O2 to H2O and generate ATP

  14. Mitochondria • Spherical to oval • about 1 micron diameter • # mito./cell increases with demand for respiration; 300-1000/root tip cell • Double-membrane bound • outer smooth • inner folds forming cristae • controls movement in/out • site of electron transportm • Matrix • soluble phase • site of TCA cycle; DNA, RNA, ribosomes cristae matrix

  15. Alternate Fates of Glucose C • Not all C respired to CO2 • Intermediates of respiration branch off: • amino acids • pentoses for cell wall structure • nucleotides • porphyrin biosynthesis • fatty acid synthesis • lignin precursors • precursors for carotenoid synthesis, hormones

  16. Factors Affecting Resp. Rate • [Substrate] • [ATP] • [Oxygen] • Temperature • Plant type • Plant organ • Plant age

  17. Factors: Substrate Availability • Resp. higher right after sundown compared to right before sunrise due to [S] • Shaded leaves respire slower than lighted leaves • Starvation of plant tissue results in utilization of proteins • High [ATP] in cell and get negative feedback on resp.

  18. Factors: [Oxygen] • No effect until [O2] < 1% • Cyt oxidase not sensitive to O2 until 0.05% • O2 diffuses in water 10,000 X slower than in air • Some plants have intercellular air system, e.g., aerenchyma in shoots and roots (rice) • Very low levels of O2 see accelerated breakdown of sugars to ethanol and CO2 evolved = Pasteur Effect

  19. Factors: Temperature • Q10 for respiration is 2.0 - 2.5 between 5 and 25C • Q10 = rate of process at one temperature divided by the rate at 10C lower temp. • Decreases with most plant tissues at 30-35C • O2 being used so fast, it can’t diffuse fast enough into tissues • Tropical regions - 70-80% PS C lost to resp. due to high night temperatures and resp. rates

  20. Factors: Plant Type/Organ/Age • Resp. rate tends to increase with age of plant • Young trees lose about 1/3 daily PS C to resp. and doubles with older trees as ratio of PS/Non-PS tissue decreases • Greater metabolic activity = greater resp. rates • Root tips, dev. buds and meristematic regions in general have higher respiration rates • In veg. tissues, resp. decreases from the tip to the mature regions • Seeds - low resp. rates, dormant, desiccation results in slowdown of respiration

  21. Factors: Plant Type/Organ/Age (cont.) • Ripening Fruit • Resp. high when young cells are dividing and growing • Climacteric Fruit (apples, tomatoes) • Sharp increase in rate immediately before fruit ripening = climacteric rise in respiration • Coincides with full ripeness and flavor and preceded by huge increase in ethylene production • This leads to senescence and decrease in respiration • Non-climacteric Fruit • Citrus, cherries, grapes, pineapple, strawberries • Insensitive to ethylene

  22. Controlled Atmosphere Storage • Lower O2 (2% - 3%) & raise CO2 (5% - 10%) • slows down resp. • No ethylene • high CO2 also inhibits ethylene synthesis • Temps. typically about -1 to -0.5C • Pick apples in Sept./Oct. when green and immature and store in CA • expose to normal air with ethylene when ready to sell fresh apples in March

  23. Cyanide Resistant Respiration • Aerobic resp. (cyt oxidase) in plants and animals inhibited by CN- and N3- (azide) • bind to Fe in enzyme and halts e- transport • Animals: CN causes resp. to decrease fast, virtually irreversible and fatal • Plants: display a 10-25% CN-resistant resp. and alternate pathway for electron flow • electron flow branches off to alternate oxidase • less ATP produced

  24. Cyanide Resistant Respiration (cont.) • Metabolic Role? • No clear role • Operates when cyt oxidase poisoned • Energy overflow hypothesis • overflow for electrons when resp. rate exceeds demand for ATP; high with high carbo. levels • Skunk cabbage, Voodoo lily, Stinking lily: CN-res. pathway causes temp. of spadix to increase 10-20C. • volatilization of odiferous cmpds which attract pollinators

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