Chapter 8 Photosynthesis Dr. Joseph Silver

1. Chapter 8PhotosynthesisDr. Joseph Silver

2. this chapter deals with1. what is photosynthesis2. discovery of photosynthesis3. pigments involved in photosynthesis4. the light reaction5. the dark reaction6. photorespiration (C3 & C4 plants)

5. photosynthesisdepends on cells capturingthe energy in somewavelengths of visible light

6. it is estimated that only about1%of the suns energyis captured by plants

7. there are two typesof photosynthesis1.anoxygenic (does not produce oxygen)2.oxygeneic (produces oxygen)

8. anoxygenic photosynthesistakes place inpurple, green sulfur, green nonsulfur, & heliobacteriain a previous chapter we learned about theevolution of metabolismanoxygenic photosynthesis was mentionedas a very primitive form of photosynthesiswhere energy (energized electrons)is gotten from molecules without oxygensuch as H2S or FeCl3

9. oxygenic photosynthesistakes place incyanobacteria, 7 groups of algae, all land plantsthis is modern photosynthesisresponsible for oxygen in our atmospherewater is used as an electron donor

11. we will concentrate onoxygenic photosynthesiswhich takes place in achloroplast

12. chloroplasts- have an outer and inner membrane- the inner membrane has many folds- thylakoid surface contains photosynthetic pigments- a stalk of thylakoids forms a grana- the grana are surrounded by a fluid stroma- the stroma contains glucose forming enzymes- chloroplast DNA is in the stroma

14. there are 3 steps to photosynthesis1. capture light energy2. make ATP & NADPHsteps 1 & 2 require light 3. use ATP & NADPH to make glucosestep 3 (carbon fixation) does not need light

16. photosynthesis6C02 + 12H2O + light(energy)  C6H12O6 + 6H2O + 6O2you should see that this equationis the reverse of cellular respirationyou need to know this equation

17. outer membraneinner membraneintermembrane spacethylakoidstromapigmentsphotosystemsplastoglobule

20. Greeks – growth from soilJan Helmont(1600s) – growth from soil & water Joseph Priestly(1700s) – plants add “life” to airJan Ingenhousz(1700s) – O2 off & carbon to carbohydrateF.F.Blackman(1900s) – only one part needs lightRobin Hill(1950s) – use of radioactive labels to trace chemicals through a biological pathway found that electrons from water used to make sugar

21. let’s digress for a momentandtalk about a subjectno one wants to talk abouttransmutation

22. seed + water + soil = growth of a plantseed weighs 0.6 grams – soil weighs 200 kilogramswater with pure waterin a few years the soil weighs 188 kilogramsthe tree weighs 920 kilogramsthe water in the tree weighs 600 kilograms920 – 600 = 320 – 12 =308 (where did the 308 come from)

23. visible light is only a small part of theelectromagnetic spectrum

26. a particle of light = a photona chemical which absorbs light energy = a pigmentthe shorter the wavelength of lightthe more energy the light contains

27. pigments absorb lightwhichcause excited electrons to be releasedwhichare picked up by electron carrierswhichwill be used to construct ATP & sugar

30. plant cells contain 3 types of pigments1. chlorophyll a2. chlorophyll b3. carotenoids

32. the main pigment = chlorophyll a2nd is chlorophyll b3rd = carotenoids (also antioxidants)

33. plant pigments absorb energyin the violet, blue and red areastheydo notabsorb in the green areathey look green becausegreen is nor absorbedgreen is reflected away from the chloroplasts

34. a photon of lightexcites electrons in the chlorophyll moleculewhichis passed among the double and triple bondsof chlorophyll and passed from molecule to moleculeuntil it reaches the reaction center

36. SOlets do the light reactionlight dependent reaction

38. antenna complex = microdomainphotosystem II and photosystem Ia whole bunch of pigment moleculesin a protein matrixdesigned to do a job1. which is to capture the energy in light2. to transfer energy from molecule to molecule3. until it reaches the reaction center chlorophyll 4. where energized electrons are released5. into the thylakoid lumen6. while producing a proton gradient and NADPH

40. Photosystem II1. photons of light energize chlorophyll (680)2. cause energy to pass from pigment to pigment3. at reaction center energized electron released 4. to an electron transport complex5. H+ released to from proton gradient6. ATP synthase use H+ to make ATP to use in Calvin cycle to make sugar7. pair of electrons carried to photosystem I8. water oxidized to release H+, e-, & O which regenerate chlorophyll 9. and oxygen is released

41. Photosystem I1. energized electrons from photosystem II(700)2. energizes chlorophylls which pass3. electrons to reaction center4. which releases energized electrons5. to a second electron transport chain6. which energizes NADP to NADPH7. which will be used in Calvin cycle to make sugar

42. just as in mitochondriathe energized NADs go to the dark cycleand the proton gradient is used to make ATPwhichgoes to the dark cyclewhereenergy is used to make sugar from CO2

45. the Calvin cyclethe dark reactioncarbon fixation cycleC3 photosynthesisthe light-independent reactionwhere the ATP and NADPHare used to take CO2and make sugarwhich will go to a mitochondrionand be used to make ATP ??????

46. the dark reactionconvertsinorganic carbontoorganic carbon

47. the dark reactionthe Calvin Cycle is similar tothe Krebs cyclein thata molecule entersand goes through a cycleand regeneratesthe starting compound

48. The Calvin Cyclethe light-independent reactionhas 3 parts1. carbon fixation2. chemical reduction3. regeneration of RuBP

49. in the stroma of a chloroplastRuBP(ribulose 1,5-bisphosphate) [5 carbons]reacts with CO2 (1 carbon)to form3-phosphoglycerate (PGA) {3 carbons}

50. you need to go through thecycle twice to make1 molecule of glucose