Metabolisme 3


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Metabolisme 3

  1. 1.
  2. 2. Photosynthesis<br />By. DhitaAyu PS,S.Pd.<br />
  3. 3. Photosynthesis in Overview<br />Process by which plants and other autotrophs store the energy of sunlight into sugars.<br />Requires sunlight, water, and carbon dioxide.<br />Overall equation:<br />6 CO2 + 6 H20  C6H12O6 + 6 O2<br />
  4. 4. 4<br />Question:<br />Where does photosynthesis take place?<br />
  5. 5. Leaf Structure<br />Most photosynthesis occurs in the palisade layer.<br />Gas exchange of CO2 and O2 occurs at openings called stomata surrounded by guard cells on the lower leaf surface.<br />Palisade<br />Spongy<br />
  6. 6. 6<br />Nucleus<br />Cell Wall<br />Chloroplast<br />Central Vacuole<br />Mesophyll Cell of Leaf<br />Photosynthesis occurs in these cells!<br />
  7. 7. Chloroplast Structure<br />Inner membrane called the thylakoid membrane.<br />Thickened regions called thylakoids. A stack of thylakoids is called a granum. (Plural – grana)<br />Stroma is a liquid surrounding the thylakoids.<br />
  8. 8. 8<br />Question:<br />Why are plants green?<br />
  9. 9. 9<br />Chlorophyll Molecules<br />Located in the thylakoid membranes<br />Chlorophyll have Mg+ in the center<br />Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red-660 nm are most important)<br />Plants are green because the green wavelength is reflected, not absorbed.<br />
  10. 10. Pigments<br />Chlorophyll A is the most important photosynthetic pigment. <br />Other pigments called antenna or accessory pigments are also present in the leaf.<br />Chlorophyll B<br />Carotenoids (orange / red)<br />Xanthophylls (yellow / brown)<br />These pigments are embedded in the membranes of the chloroplast in groups called photosystems.<br />
  11. 11. 11<br />Parts of Photosynthesis<br />
  12. 12. Photosynthesis: The Chemical Process<br />Occurs in two main phases.<br />Light reactions<br />Dark reactions (The Calvin Cycle)<br />Light reactions are the “photo” part of photosynthesis. Light is absorbed by pigments.<br />Dark reactions are the “synthesis” part of photosynthesis. Trapped energy from the sun is converted to the chemical energy of sugars. <br />
  13. 13. Light Reactions<br />Light-dependent reactions occur on the thylakoid membranes.<br />Light and water are required for this process.<br />Energy storage molecules are formed. (ATP and NADPH)<br />Oxygen gas is made as a waste product.<br />
  14. 14.
  15. 15.
  16. 16. Fig. 10.12<br />
  17. 17. During the light reactions, there are two possible routes for electron flow: cyclic and noncyclic.<br />Noncyclic electron flow, the predominant route, produces both ATP and NADPH.<br />When photosystem II absorbs light, an excited electron is captured by the primary electron acceptor, leaving the reaction center oxidized.<br />An enzyme extracts electrons from water and supplies them to the oxidized reaction center.<br />This reaction splits water into two hydrogen ions and an oxygen atom which combines with another to form O2.<br />
  18. 18. Photoexcitedelectrons pass along an electron transport chain before ending up at an oxidized photosystem I reaction center.<br />As these electrons pass along the transport chain, their energy is harnessed to produce ATP.<br />The mechanism of noncyclicphotophosphorylation is similar to the process on oxidative phosphorylation.<br />
  19. 19. 5. At the bottom of this electron transport chain, the electrons fill an electron “hole” in an oxidized P700 center.<br />6. This hole is created when photons excite electrons on the photosystem I complex. <br />The excited electrons are captured by a second primary electron acceptor which transmits them to a second electron transport chain.<br />Ultimately, these electrons are passed from the transport chain to NADP+, creating NADPH.<br />NADPH will carry the reducing power of these high-energy electrons to the Calvin cycle.<br />
  20. 20. 20<br />e-<br />Primary<br />Electron<br />Acceptor<br />SUN<br />e-<br />ATP<br />produced<br />by ETC<br />e-<br />Photons<br />e-<br />P700<br />Accessory<br />Pigments<br />Photosystem I<br />Cyclic Electron Flow<br />Pigments absorb light energy & excite e- of Chlorophyll a to produce ATP <br />
  21. 21. Dark Reactions<br />Dark reactions (light-independent) occur in the stroma.<br />Carbon dioxide is “fixed” into the sugar glucose.<br />The actual sugar product of the Calvin cycle is not glucose, but a three-carbon sugar, glyceraldehyde-3-phosphate (G3P).<br />For the net synthesis of one G3P molecule, the cycle must take place three times, fixing three molecules of CO2.<br />To make one glucose molecules would require six cycles and the fixation of six CO2 molecules.<br />ATP and NADPH molecules created during the light reactions power the production of this glucose.<br />
  22. 22. The Calvin cycle has three phases.<br />1. In the carbon fixation phase, each CO2 molecule is attached to a five-carbon sugar, ribulosebisphosphate (RuBP).<br />This is catalyzed by RuBPcarboxylase or rubisco.<br />The six-carbon intermediate splits in half to form two molecules of 3-phosphoglycerate per CO2.<br />
  23. 23. Fig. 10.17.1<br />
  24. 24. During reduction, each 3-phosphoglycerate receives another phosphate group from ATP to form 1,3 bisphosphoglycerate.<br />A pair of electrons from NADPH reduces each 1,3 bisphosphoglycerate to G3P.<br />The electrons reduce a carboxyl group to a carbonyl group.<br />
  25. 25. Fig. 10.17.2<br />
  26. 26. If our goal was to produce one G3P net, we would start with 3 CO2 (3C) and three RuBP (15C).<br />After fixation and reduction we would have six molecules of G3P (18C). <br />One of these six G3P (3C) is a net gain of carbohydrate.<br />This molecule can exit the cycle to be used by the plant cell.<br />The other five (15C) must remain in the cycle to regenerate three RuBP.<br />
  27. 27. In the last phase, regeneration of the CO2 acceptor (RuBP), these five G3P molecules are rearranged to form 3 RuBP molecules.<br />To do this, the cycle must spend three more molecules of ATP (one per RuBP) to complete the cycle and prepare for the next.<br />
  28. 28.
  29. 29. For the net synthesis of one G3P molecule, the Calvin recycle consumes nine ATP and six NAPDH.<br />It “costs” three ATP and two NADPH per CO2.<br />The G3P from the Calvin cycle is the starting material for metabolic pathways that synthesize other organic compounds, including glucose and other carbohydrates.<br />