1 / 60

Essential Knowledge 2A2

PHOTOSYNTHESIS. Essential Knowledge 2A2. How the photosystems collect light energy and convert it to chemical energy. How photosystem II produces ATP by chemiosmosis in the light reactions. How the double membrane structure of the chloroplasts enable their function in chemiosmosis .

lethia
Télécharger la présentation

Essential Knowledge 2A2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PHOTOSYNTHESIS Essential Knowledge 2A2

  2. How the photosystems collect light energy and convert it to chemical energy. How photosystem II produces ATP by chemiosmosis in the light reactions. How the double membrane structure of the chloroplasts enable their function in chemiosmosis. How photosystem I produces NADPH in the light reactions.

  3. How the Calvin cycle uses the products of the light reactions to synthesize sugar (G3P). The causes of and metabolic costs of photorespiration. The evolutionary adaptations of C4 and CAM plants that enable them to efficiently perform the Calvin cycle in hot, dry habitats. The commonalities and distinctions between photosynthesis in chloroplasts and aerobic respiration in mitochondria.

  4. light-dependent reactions • Calvin cycle • light-independent reactions • photosystem • photosystem II • photosystem I • carbon fixation • absorption spectrum • pigments • chlorophyll • chlorophyll a • chlorophyll b • action spectrum • carotenoid • NADPH • cyclic photophosphorylation • noncyclicphotophosphorylation

  5. Calvin cycle • Rubisco • RuBP • glyceraldehyde-3-phosphate • C3 photosynthesis • photorespiration • C4 photosynthesis • crassulacean acid metabolism (CAM)

  6. Photosynthesis

  7. Photosynthesis Overview • Energy for all life on Earth ultimately comes from photosynthesis 6CO2 + 12H2O C6H12O6 + 6H2O + 6O2 • Oxygenic photosynthesis is carried out by • Cyanobacteria • 7 groups of algae • All land plants – chloroplasts

  8. Thylakoid membrane – internal membrane • Contains chlorophyll and other photosynthetic pigments • Pigments clustered into photosystems • Grana – stacks of flattened sacs of thylakoid membrane • Stroma lamella – connect grana • Stroma – semiliquid surrounding thylakoid membranes Chloroplast

  9. Stages • Light-dependent reactions • Require light • Capture energy from sunlight • Make ATP and reduce NADP+ to NADPH • Carbon fixation reactions or light-independent reactions • Does not require light • Use ATP and NADPH to synthesize organic molecules from CO2

  10. Discovery of Photosynthesis • Jan Baptista van Helmont (1580–1644) • Demonstrated that the substance of the plant was not produced only from the soil • Joseph Priestly (1733–1804) • Living vegetation adds something to the air • Jan Ingen-Housz (1730–1799) • Proposed plants carry out a process that uses sunlight to split carbon dioxide into carbon and oxygen (O2 gas)

  11. F.F. Blackman (1866–1947) • Came to the startling conclusion that photosynthesis is in fact a multistage process, only one portion of which uses light directly • Light versus dark reactions • Enzymes involved

  12. C. B. van Niel (1897–1985) • Found purple sulfur bacteria do not release O2 but accumulate sulfur • Proposed general formula for photosynthesis • CO2 + 2 H2A + light energy → (CH2O) + H2O + 2 A • Later researchers found O2 produced comes from water • Robin Hill (1899–1991) • Demonstrated Niel was right that light energy could be harvested and used in a reduction reaction

  13. Pigments • Molecules that absorb light energy in the visible range • Light is a form of energy • Photon – particle of light • Acts as a discrete bundle of energy • Energy content of a photon is inversely proportional to the wavelength of the light • Photoelectric effect – removal of an electron from a molecule by light

  14. Absorption spectrum • When a photon strikes a molecule, its energy is either • Lost as heat • Absorbed by the electrons of the molecule • Boosts electrons into higher energy level • Absorption spectrum – range and efficiency of photons molecule is capable of absorbing

  15. Organisms have evolved a variety of different pigments • Only two general types are used in green plant photosynthesis • Chlorophylls • Carotenoids • In some organisms, other molecules also absorb light energy

  16. Chlorophyll a • Main pigment in plants and cyanobacteria • Only pigment that can act directly to convert light energy to chemical energy • Absorbs violet-blue and red light • Chlorophyll b • Accessory pigment or secondary pigment absorbing light wavelengths that chlorophyll a does not absorb Chlorophylls

  17. Pigments

  18. Structure of chlorophyll • porphyrin ring • Complex ring structure with alternating double and single bonds • Magnesium ion at the center of the ring • Photons excite electrons in the ring • Electrons are shuttled away from the ring

  19. Action spectrum • Relative effectiveness of different wavelengths of light in promoting photosynthesis • Corresponds to the absorption spectrum for chlorophylls

  20. Carotenoids • Carbon rings linked to chains with alternating single and double bonds • Can absorb photons with a wide range of energies • Also scavenge free radicals – antioxidant • Protective role • Phycobiloproteins • Important in low-light ocean areas

  21. Photosystem Organization • Antenna complex • Hundreds of accessory pigment molecules • Gather photons and feed the captured light energy to the reaction center • Reaction center • 1 or more chlorophyll a molecules • Passes excited electrons out of the photosystem

  22. Also called light-harvesting complex Captures photons from sunlight and channels them to the reaction center chlorophylls In chloroplasts, light-harvesting complexes consist of a web of chlorophyll molecules linked together and held tightly in the thylakoid membrane by a matrix of proteins Antenna complex

  23. Transmembrane protein–pigment complex When a chlorophyll in the reaction center absorbs a photon of light, an electron is excited to a higher energy level Light-energized electron can be transferred to the primary electron acceptor, reducing it Oxidized chlorophyll then fills its electron “hole” by oxidizing a donor molecule Reaction center

  24. Light-Dependent Reactions • Primary photoevent • Photon of light is captured by a pigment molecule • Charge separation • Energy is transferred to the reaction center; an excited electron is transferred to an acceptor molecule • Electron transport • Electrons move through carriers to reduce NADP+ • Chemiosmosis • Produces ATP Capture of light energy

  25. Cyclic photophosphorylation • In sulfur bacteria, only one photosystem is used • Generates ATP via electron transport • Anoxygenic photosynthesis • Excited electron passed to electron transport chain • Generates a proton gradient for ATP synthesis

  26. Chloroplasts have two connected photosystems • Oxygenic photosynthesis • Photosystem I (P700) • Functions like sulfur bacteria • Photosystem II (P680) • Can generate an oxidation potential high enough to oxidize water • Working together, the two photosystems carry out a noncyclic transfer of electrons that is used to generate both ATP and NADPH

  27. Photosystem I transfers electrons ultimately to NADP+, producing NADPH • Electrons lost from photosystem I are replaced by electrons from photosystem II • Photosystem II oxidizes water to replace the electrons transferred to photosystem I • 2 photosystems connected by cytochrome/ b6-f complex

  28. Noncyclic photophosphorylation • Plants use photosystems II and I in series to produce both ATP and NADPH • Path of electrons not a circle • Photosystems replenished with electrons obtained by splitting water • Z diagram

  29. Photosystem II • Resembles the reaction center of purple bacteria • Core of 10 transmembrane protein subunits with electron transfer components and two P680 chlorophyll molecules • Reaction center differs from purple bacteria in that it also contains four manganese atoms • Essential for the oxidation of water • b6-f complex • Proton pump embedded in thylakoid membrane

  30. Photosystem I • Reaction center consists of a core transmembrane complex consisting of 12 to 14 protein subunits with two bound P700 chlorophyll molecules • Photosystem I accepts an electron from plastocyanin into the “hole” created by the exit of a light-energized electron • Passes electrons to NADP+ to form NADPH

  31. Electrochemical gradient can be used to synthesize ATP • Chloroplast has ATP synthase enzymes in the thylakoid membrane • Allows protons back into stroma • Stroma also contains enzymes that catalyze the reactions of carbon fixation – the Calvin cycle reactions Chemiosmosis

  32. Noncyclicphotophosphorylation generates • NADPH • ATP • Building organic molecules takes more energy than that alone • Cyclic photophosphorylation used to produce additional ATP • Short-circuit photosystem I to make a larger proton gradient to make more ATP Production of additional ATP

  33. Carbon Fixation – Calvin Cycle • To build carbohydrates cells use • Energy • ATP from light-dependent reactions • Cyclic and noncyclic photophosphorylation • Drives endergonic reaction • Reduction potential • NADPH from photosystem I • Source of protons and energetic electrons

  34. Calvin cycle • Named after Melvin Calvin (1911–1997) • Also called C3 photosynthesis • Key step is attachment of CO2 to RuBP to form PGA • Uses enzyme ribulose bisphosphate carboxylase/oxygenase or rubisco

  35. 3 phases • Carbon fixation • RuBP + CO2 → PGA • Reduction • PGA is reduced to G3P • Regeneration of RuBP • PGA is used to regenerate RuBP • 3 turns incorporate enough carbon to produce a new G3P • 6 turns incorporate enough carbon for 1 glucose

  36. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

  37. Output of Calvin cycle • Glucose is not a direct product of the Calvin cycle • G3P is a 3 carbon sugar • Used to form sucrose • Major transport sugar in plants • Disaccharide made of fructose and glucose • Used to make starch • Insoluble glucose polymer • Stored for later use

  38. Energy cycle • Photosynthesis uses the products of respiration as starting substrates • Respiration uses the products of photosynthesis as starting substrates • Production of glucose from G3P even uses part of the ancient glycolytic pathway, run in reverse • Principal proteins involved in electron transport and ATP production in plants are evolutionarily related to those in mitochondria

More Related