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 O 2, 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 6CO 2 + 12H 2 O + light  C 6 H 12 O 6 + 6O 2 + 6H 2 O −Many intermediate steps to process, and glucose not immediate 1 st product

7. Photosynthesis CO 2 reaches chloroplasts in mesophyll cells by diffusion (stomata -> leaf interior) Use of fossil fuels, deforestation, and other human activities add more CO 2 to atmosphere than is removed −Has potential to cause global increases in temperature −May enhance photosynthesis

8. Photosynthesis  Less than 1% of all H 2 O absorbed by plants used in photosynthesis Most transpired or incorporated into plant materials  H 2 O source of e - in photosynthesis and O 2 released as by-product  If H 2 O in short supply or light intensities too high, stomata close and reduce supply of CO 2 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 CO 2 can be limiting

11. Photosynthesis  If light and temps too high: ratio of CO 2 to O 2 inside leaves may change Accelerates photorespiration - uses O 2 and releases CO 2 −May help some plants survive under adverse conditions  If light intensity too high: photooxidation - results in destruction of chlorophyll  If H 2 O in short supply or light intensities too high: stomata close and reduce supply of CO 2 available for photosynthesis

12. Photosynthesis  Several types of chlorophyll molecules Mg end captures light Lipid tail anchors into thylakoid membrane 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: Thylakoid membranes of chloroplasts H 2 O split apart, releasing e - and H + ; O 2 released e - pass along e - transport system ATP produced NADP reduced to NADPH (used in light-independent reactions)

15. Photosynthesis Major Steps of Photosynthesis  Light-Independent Reactions: Stroma of chloroplasts Utilize ATP and NADPH to form sugars Calvin Cycle −CO 2 combines with RuBP (ribulose bisphosphate) 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 photosystem II Photosystem II before photosystem I Both produce ATP Both photosystem I and photosystem II needed to produce NADPH and O 2 as result of e - flow

18. Photosynthesis A Closer Look: Light-Dependent Reactions  Photosystem I = chlorophyll a, small amount of chlorophyll b, carotenoid pigment, and P 700 P 700 = 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 P 700  Photosystem II = chlorophyll a, B-carotene, small amounts of chlorophyll b, and P 680 Pheophytin (Pheo) - primary e - acceptor

19. Photosynthesis A Closer Look: Light-Dependent Reactions

20. Photolysis - H 2 O-splitting, Photosystem II – Light photons absorbed by P 680, boosting e - to higher energy level – e - passed to acceptor molecule, pheophytin, then to PQ (plastoquinone), then along e - transport system to photosystem I – e - extracted from H 2 O replace e - lost by P 680 – 1 O 2, 4 H + and 4 e - produced from 2 H 2 O

21. Photosynthesis A Closer Look: Light-Dependent Reactions  e - Flow and Photophosphorylation e - transport system consists of e - 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 P 700, 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 P 700 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 H 2 O molecules and e - transport H + gradient gives ATPase in 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 CO 2 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 O 2 instead of CO 2 Allows C3 plants to survive under hot dry conditions −Dissipates ATP and accumulated e -, prevents photooxidation When stomata closed, O 2 accumulates and photorespiration more likely Produces 2-C phosphoglycolic acid (processed in perioxisomes) −Forms CO 2 and PGA -> reenter Calvin cycle −No ATP formed

27. Photosynthesis A Closer Look: Light-Independent Reactions  C 4 Pathway - produces 4-C compound instead of 3-C PGA during initial steps of light-independent reactions C 4 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  C 4 Pathway CO 2 converted to organic acids in mesophyll cells PEP (phosphoenolpyruvate) and CO 2 combine, with aid of PEP carboxylase Form 4-C oxaloacetic acid instead of PGA PEP carboxylase converts CO 2 to carbohydrate at lower CO 2 concentrations than does rubisco −No photorespiration

29. Photosynthesis A Closer Look: Light-Independent Reactions  C 4 Pathway CO 2 transported as organic acids to bundle sheath cells, released and enters Calvin cycle CO 2 concentration high in bundle sheath = little photorespiration C 4 plants photosynthesize at higher temps than C 3 plants −Costs 2 ATP for C 4 photosynthesis

30. Photosynthesis A Closer Look: Light-Independent Reactions  CAM Photosynthesis - similar to C 4 photosynthesis as 4-C compounds produced during light-independent reactions, however: Organic acids accumulate at night (stomata open) Converted back to CO 2 during day for use in Calvin cycle (stomata closed) – Adaptation to limited H 2 O supply and high light intensity habitat

31. Respiration  Respiration - release of energy from glucose molecules broken down to individual CO 2 molecules Initiated in cytoplasm and completed in mitochondria Aerobic respiration needs O 2 C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + energy

32. Respiration  Anaerobic respiration and fermentation - carried on in absence of O 2 Release less energy than aerobic respiration Fermentation equations: −C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2 + 2ATP −C 6 H 12 O 6  2C 3 H 6 O 3 + 2ATP

33. Respiration Major Steps of Respiration  Glycolysis - 1st phase In cytoplasm No O 2 required Glucose converted to GA3P (glyceraldehyde 3- phosphate) 2 ATP molecules gained

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

35. Respiration A 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 H 2 O removed leaving pyruvic acid Before citric acid cycle, pyruvic acid loses CO 2 and converted to acetyl CoA No O 2 = anaerobic respiration and fermentation −H + released during glycolysis transferred back to pyruvic acid, creating ethyl alcohol or lactic acid

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

37. Respiration A Closer Look  e - Transport and Oxidative Phosphorylation Energy from NADH and FADH 2 released as H + and e - passed along e - transport system H + build up outside mitochondrial matrix = electrochemical gradient Chemiosmosis couples transport of H + into matrix with oxidative phosphorylation = formation of ATP O 2 = ultimate e - acceptor, producing H 2 O as it combines with H + Produces net gain of 36 ATP and 6 CO 2 and H 2 O

38. Respiration

40. Factors Affecting the Rate of Respiration  Temperature Increase from 20 o C to 30 o C, respiration rates double  H 2 O Medium in which enzymatic reactions take place Low H 2 O content - respiration rate reduced  O 2 Reduction in O 2 - respiration and growth rates decline

41. 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

42. 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

43. Review  Introduction  Enzymes and Energy Transfer  Photosynthesis  Respiration  Additional Metabolic Pathways  Assimilation and Digestion