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Respiration

This text provides an overview of respiration and the conversion of carbohydrates in plants, including the equations for aerobic and anaerobic respiration, the efficiency of energy yield, and the three stages of respiration. It also covers the structure and function of mitochondria and the alternate fates of glucose. The factors affecting respiration rate are discussed, including substrate availability, oxygen levels, temperature, plant type, organ, and age.

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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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