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Plant Metabolism

Plant Metabolism. Chapter 10. Outline. Introduction Enzymes and Energy Transfer Photosynthesis Respiration Additional Metabolic Pathways Assimilation and Digestion. Introduction. Photosynthesis - converts light energy to usable form Respiration - releases stored energy

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Plant Metabolism

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  1. Plant Metabolism Chapter 10

  2. Outline • Introduction • Enzymes and Energy Transfer • Photosynthesis • Respiration • Additional Metabolic Pathways • Assimilation and Digestion

  3. Introduction • Photosynthesis -converts light energy to usable form • Respiration -releases stored energy • Facilitates growth, development and reproduction • Metabolism -sum of all interrelated biochemical processes in living organisms • Animals rely on green plants for O2, food, shelter and other products

  4. Enzymes and Energy Transfer • Enzymes regulate metabolic activities • Anabolism -forming chemical bonds to build molecules • Photosynthesis • Catabolism -breaking chemical bonds • Cellular respiration • Photosynthesis-respiration Cycle involves transfer of energy via oxidation-reduction reactions

  5. Enzymes and Energy Transfer • Oxidation-Reduction Reactions • Oxidation -loss of electron(s) • Reduction -gain of electron(s) • Oxidation of one compound usually coupled with reduction of another • H atom lost during oxidation and gained during reduction • O usually final acceptor of electron

  6. Photosynthesis • Energy for most cellular activity = adenosine triphosphate (ATP) • Plants make ATP using light as energy source • Takes place in chloroplasts and other green parts of organisms 6CO2 + 12H2O + light C6H12O6 + 6O2 + 6H2O • Many intermediate steps to process, and glucose not immediate 1st product

  7. Photosynthesis • CO2reaches chloroplasts in mesophyll cells by diffusion (stomata -> leaf interior) • Use of fossil fuels, deforestation, and other human activities add more CO2 to atmosphere than is removed • Has potential to cause global increases in temperature • May enhance photosynthesis

  8. Photosynthesis • Less than 1% of all H2O absorbed by plants used in photosynthesis • Most transpired or incorporated into plant materials • H2O source ofe-in photosynthesis and O2 released as by-product • If H2O in short supply or light intensities too high, stomata close and reduce supply of CO2 available for photosynthesis

  9. Photosynthesis • ~40% of radiant energy received on earth visible light • Violet to blue and red-orange to red wavelengths absorbed • Green light reflected • Leaves absorb ~80% of visible light reaching them • Light intensity varies with time of day, season, altitude, latitude, and atmospheric composition Visible light passed through prism

  10. Photosynthesis • Plants vary considerably in light intensities needed for optimal photosynthetic rates • Temperature and amount of CO2 can be limiting

  11. Photosynthesis • If light and temps too high:ratio of CO2 to O2inside leaves may change • Accelerates photorespiration - uses O2and releases CO2 • May help some plants survive under adverse conditions • If light intensity too high: photooxidation - results in destruction of chlorophyll • If H2O in short supply or light intensities too high: stomata close and reduce supply of CO2available for photosynthesis

  12. Photosynthesis • Several types of chlorophyll molecules • Mg end captures light • Lipid tail anchors into thylakoidmembrane • Most plants contain chlorophyll a(blue-green color) and chlorophyll b(yellow-green color) • Chlorophyll b transfers energy from light to chlorophyll a Chlorophyll a molecule

  13. Photosynthesis • Other photosynthetic pigments include carotenoids(yellow and orange), phycobilins (blue or red, in cyanobacteria and red algae), and several other types of chlorophyll • Ca. 250-400 pigment molecules grouped in light-harvesting complex = photosynthetic unit • Two types of photosynthetic units work together in light-dependent reactions • Two phases of photosynthesis: • Light-dependent reactions • Light-independent reactions

  14. Photosynthesis Major Steps of Photosynthesis • Light-Dependent Reactions: • Thylakoidmembranes of chloroplasts • H2O split apart, releasing e-and H+; O2 released • e-pass along e-transport system • ATP produced • NADP reduced to NADPH (used in light-independent reactions)

  15. PhotosynthesisMajor Steps of Photosynthesis • Light-Independent Reactions: • Stromaof chloroplasts • Utilize ATP and NADPH to form sugars • Calvin Cycle • CO2 combines with RuBP (ribulosebisphosphate) and combined molecules converted to sugars (glucose) • Uses ATP and NADPH produced during light-dependent reactions

  16. Photosynthesis A Closer Look: Light-Dependent Reactions • Each pigment has own distinctive pattern of light absorption = absorption spectrum • When pigments absorb light, energy levels of e- raised • Energy from excited e- released when drops back to ground state • In photosynthesis, energy stored in chemical bonds

  17. Photosynthesis A Closer Look: Light-Dependent Reactions • Two types of photosynthetic units: photosystem I and photosystemII • Photosystem II before photosystem I • Both produce ATP • Both photosystem I and photosystem II needed to produce NADPH and O2as result of e- flow

  18. Photosynthesis A Closer Look: Light-Dependent Reactions • Photosystem I = chlorophyll a, small amount of chlorophyll b, carotenoid pigment, and P700 • P700 = reaction-center molecule which uses light energy • Remaining pigments = antenna pigments • Gather and pass light energy to reaction center • Fe-S proteins -primary e-acceptors, first to receive e- from P700 • Photosystem II = chlorophyll a, B-carotene, small amounts of chlorophyll b, and P680 • Pheophytin (Pheo) -primary e-acceptor

  19. Photosynthesis A Closer Look: Light-Dependent Reactions

  20. Photosynthesis A Closer Look: Light-Dependent Reactions • Photolysis - H2O-splitting, Photosystem II • Light photons absorbed by P680, boosting e-to higher energy level • e-passed to acceptor molecule, pheophytin, then to PQ (plastoquinone), then along e-transport system to photosystemI • e-extracted from H2O replacee-lost by P680 • 1 O2, 4 H+and 4 e-produced from 2 H2O

  21. Photosynthesis A Closer Look: Light-Dependent Reactions • e- Flow and Photophosphorylation • e-transport system consists ofe-transfer molecules • Photons move across thylakoid membrane by chemiosmosis • Phosphorylation - ATP formed from ADP

  22. Photosynthesis A Closer Look: Light-Dependent Reactions • Photosystem I • Light absorbed by P700, boosting e-to higher energy level • e-passed to Fe-S acceptor molecule, Fd (ferredoxin), then to FAD (flavin adenine dinucleotide). • NADP reduced to NADPH • e-removed from P700 replaced by e-from photosystem II.

  23. Photosynthesis A Closer Look: Light-Dependent Reactions • Chemiosmosis • Net accumulation of H+in thylakoid lumen occurs from splitting of H2Omolecules and e- transport • H+gradient givesATPasein thylakoid membrane potential to move H+ from lumen to stroma • Movement of H+across membrane = source of energy for ATP synthesis

  24. Photosynthesis A Closer Look: Light-Independent Reactions • Calvin Cycle • 6 CO2 combine with 6 RuBP(ribulose 1,5-bisphosphate) with aid of rubisco • Results in 12 3-C molecules of 3PGA (3-phosphoglyceric acid) • NADPH and ATP supply energy and e- reducing 3PGA to GA3P (glyceraldehyde 3-phosphate) • 10 of 12 GA3P restructured, using 6 ATP, into 6 5-C RuBP • Net gain of 2 GA3P -> converted to carbohydrates or used to make lipids and amino acids

  25. The Calvin Cycle

  26. Photosynthesis A Closer Look: Light-Independent Reactions • Photorespiration -competes with C-fixing role of photosynthesis • Rubisco fixes O2instead of CO2 • Allows C3 plants to survive under hot dry conditions • Dissipates ATP and accumulated e-, prevents photooxidation • When stomata closed, O2accumulates and photorespiration more likely • Produces 2-C phosphoglycolicacid (processed in perioxisomes) • Forms CO2and PGA -> reenter Calvin cycle • No ATP formed

  27. Photosynthesis A Closer Look: Light-Independent Reactions • C4 Pathway -produces 4-C compound instead of 3-C PGA during initial steps of light-independent reactions • C4 plants - tropical grasses and plants of arid regions • Kranz anatomy • Mesophyll cells with smaller chloroplasts with well-developed grana • Bundle sheath cells with large chloroplasts with numerous starch grains

  28. Photosynthesis A Closer Look: Light-Independent Reactions • C4 Pathway • CO2 converted to organic acids in mesophyllcells • PEP (phosphoenolpyruvate) and CO2 combine, with aid of PEP carboxylase • Form 4-C oxaloaceticacid instead of PGA • PEP carboxylase converts CO2 to carbohydrate at lower CO2 concentrations than does rubisco • No photorespiration

  29. Photosynthesis A Closer Look: Light-Independent Reactions • C4 Pathway • CO2transported as organic acids to bundle sheath cells, released and enters Calvin cycle • CO2 concentration high in bundle sheath = little photorespiration • C4 plants photosynthesize at higher temps than C3plants • Costs 2 ATP for C4photosynthesis

  30. Photosynthesis A Closer Look: Light-Independent Reactions • CAM Photosynthesis -similar to C4 photosynthesis as 4-C compounds produced during light-independent reactions, however: • Organic acids accumulate at night (stomata open) • Converted back to CO2 during day for use in Calvin cycle (stomata closed) • Adaptation to limited H2O supply and high light intensity habitat

  31. Respiration • Respiration - release of energy from glucose molecules broken down to individual CO2 molecules • Initiated in cytoplasm and completed in mitochondria • Aerobic respiration needs O2 C6H12O6 + 6O2 6CO2 + 6H2O + energy

  32. Respiration • Anaerobic respiration and fermentation- carried on in absence of O2 • Release less energy than aerobic respiration • Fermentation equations: • C6H12O6 2C2H5OH + 2CO2 + 2ATP • C6H12O6 2C3H6O3 + 2ATP

  33. RespirationMajor Steps of Respiration • Glycolysis - 1st phase • In cytoplasm • No O2required • Glucose converted to GA3P (glyceraldehyde 3-phosphate) • 2 ATP molecules gained

  34. RespirationMajor Steps of Respiration • Citric Acid (Krebs) Cycle - 2nd stage • In fluid matrix of cristae in mitochondria • High energy e- and H+ removed • NADH, FADH2 , and small amount of ATP produced • CO2 produced as by-product • Electron transport - 3rd stage • In inner membrane of mitochondria • NADH and FADH2 donate e-to e-transport system • Produces ATP, CO2 and H2O

  35. RespirationA Closer Look • Glycolysis • 3 Steps: • Phosphorylation- glucose becomes fructose 1,6-bisphosphate • Sugar cleavage -fructose 1,6-bisphosphate split into 2 3-C GA3P (glyceraldehyde 3-phosphate) molecules • Pyruvic Acid Formation - H+, energy and H2O removed leaving pyruvicacid • Before citric acid cycle, pyruvic acid loses CO2 and converted to acetyl CoA • No O2 = anaerobic respiration and fermentation • H+released during glycolysis transferred back to pyruvic acid, creating ethyl alcohol or lactic acid

  36. RespirationA Closer Look • Citric Acid (Krebs) Cycle • Acetyl CoA combines with oxaloaceticacid (O.A.), producing citric acid • Each cycle uses 2 acetyl CoA, releases 3 CO2 and regenerates O.A. O.A. + acetyl CoA + ADP + P + 3NAD + FAD  O.A. + CoA + ATP + 3NADH + H+ + FADH2 + 2CO2 • High energy e-and H+removed, producing NADH, FADH2 and ATP.

  37. RespirationA Closer Look • e- Transport and Oxidative Phosphorylation • Energy from NADH and FADH2 released as H+and e- passed along e-transport system • H+build up outside mitochondrial matrix = electrochemical gradient • Chemiosmosiscouples transport of H+into matrix with oxidative phosphorylation = formation of ATP • O2 = ultimate e-acceptor, producing H2O as it combines with H+ • Produces net gain of 36 ATP and 6 CO2and H2O

  38. Respiration

  39. Factors Affecting the Rate of Respiration • Temperature • Increase from 20o C to 30o C, respiration rates double • H2O • Medium in which enzymatic reactions take place • Low H2O content - respiration rate reduced • O2 • Reduction in O2- respiration and growth rates decline

  40. Additional Metabolic Pathways • Other processes contribute to growth development, reproduction and survival • Includes production of sugar phosphates, nucleotides, nucleic acids, amino acids, proteins, chlorophylls, cytochromes, carotenoids, fatty acids, oils, and waxes • Secondary Metabolism -metabolic processes not required for normal growth and development • Enable plants to survive and persist under special conditions • Colors, aromas, poisons - give competitive edge • Codeine, Nicotine, Lignin, Salicin, Camphor, Menthol, Rubber

  41. Assimilation and Digestion • Assimilation -conversion of organic matter produced in photosynthesis to build protoplasm and cell walls • Sugars transformed into lipids, proteins, or other carbohydrates, such as sucrose, starch and cellulose • Digestion -conversion of starch and other insoluble carbohydrates to soluble forms • Nearly always hydrolysis process

  42. Review • Introduction • Enzymes and Energy Transfer • Photosynthesis • Respiration • Additional Metabolic Pathways • Assimilation and Digestion

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