Ch 10 Photosynthesis

1. Ch 10Photosynthesis

2. Organisms need organic compounds for: • Two types of organisms: • Two types of autotrophs (“self-feeders”): • Chemoautotrophs: • Photoautotrophs: • Photoautotrophs include: • Humans rely on photoautotrophs for: energy and carbon skeletons heterotrophs – take in organic compounds from other organisms autotrophs – make their own organic comp. obtain energy by oxidizing inorganic compounds w/out light (rare, bacteria). use light energy to produce organic compounds. plants, algae, some protists • food & oxygen

3. Photosynthesis: Metabolic process which transforms _____________ energy trapped by • ____________ into ____________ bond energy stored in _____________ and other organic molecules. • Makes energy-rich organic molecules from energy-poor molecules: • Uses _________ as a carbon source and ________ as the energy source. light chloroplasts chemical sugars CO2 and H2O CO2 light

4. LEAVES: All green plant parts have chloroplasts, but leaves are the main organs of photosynthesis in most plants. • Leaf layers: Top to bottom • Cutin: • Upper epidermis: protects • Palisade layer: • Spongy layer: contains chloroplasts and air spaces • Lower epidermis: • Mesophyll: The area including the palisade and spongy layers. • Veins are incorporated here. wax layer (also called cuticle) chloroplasts protects, contains stomata (openings) which are controlled by guard cells (w/ chloroplasts)

5. CHLOROPLAST PARTS: • Enclosed by: • Thylakoid: • Stroma: double membrane membrane pouches w/ chlorophyll (May be in grana stacks) fluid surrounding thylakoids

6. Photosynthetic Prokaryotes • No chloroplasts (DUH!) • Cyanobacteria have stacks of vesicle membranes: • Chlorophyll is built into plasma membrane or vesicle membrane • similar to grana

7. Photosynthesis Overview: Water appears on both sides because it is newly formed during the process. To simplify, show only net change in water: What does this remind you of??? 6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O 6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2 It’s the opposite of respiration

8. Now, reduce the formula to its simplest form: • Remember the C,H,O ratio for a sugar? • Photosynthesis is basically building a sugar: • Splitting Water: • People used to think the ______ released came from the ________ plants take in. • C.B. van Neil (1930’s) predicted the O2 came from ______ • He discovered this while studying bacteria that use H2S instead of water to get their H’s. These bacteria release sulfur as waste. • van Neil concluded: • Later support: CO2 + H2O → [CH2O] + O2 1:2:1 one carbon at a time! O2 CO2 H2O photosynthetic organisms need a H source and split H2O to get H. oxygen-18 tracer shows oxygen from H2O is released as O2 Mass Spectrometry equipment

9. Electrons from water are transferred to CO2 forming sugar Sugar is oxidized Endergonic

10. Photosynthesis occurs in Two Stages: • Light Reactions: • Site: • Calvin Cycle (Light Independent Reactions): • Site: convert solar energy to chemical energy (ATP and NADPH) Thylakoid membranes carbon fixation reactions reduce CO2 to carbohydrate using ATP & NADPH from Lt. Reactions Stroma fluid

11. Sunlight: Electromagnetic energy (radiation) has a behavior that is both • wavelike and particlelike. • WAVELIKE PROPERTIES: • Wavelength = distance between _____________ of waves. These range from <1nm to >1km for the Electromagnetic Spectrum. • Visible Light = 380 – 750nm wavelength: • PARTICLELIKE PROPERTIES: • Light also behaves as if it consists of particles called: photons (or quanta) • Photon = • Shorter wavelengths = _______________ energy (violet more energy than red) rhythmic disturbances of electric and magnetic fields crests The portion of the Elec. Spectrum which humans can see (ROYGBIV) fixed quantity of energy (inversely proportional to wavelength) more

12. Photosynthetic Pigments: As light meets matter, it can be reflected, transmitted, or absorbed. • Pigments: • Different pigments absorb light of different wavelengths: • The wavelengths that are absorbed: • Spectrophotometer: measures the ability of a pigment to absorb various wavelengths. • Chlorophyll a: • Accessory pigments: Absorb light & transfer the energy to chlorophyll a. • Chlorophyll b: • Carotenoids (family of pigments): • Why have several pigments??? absorb visible light each pigment has an “absorption spectrum” “disappear.” The colors we see are those reflected! Main pigment in chloroplasts (blue-green), temp. dependent yellow-green various shades of yellow and orange To absorb different (more) colors of light

13. Photooxidation of Chlorophyll • When pigments absorb photons: • Colors of absorbed light disappear from spectrum, • Photon boosts one of the pigment molecule’s ___________ from its lowest energy • state _______________________ to an orbital of higher potential energy • __________________________ • Excited state is unstable: • Thylakoid membranes contain electron acceptors which trap the excited electrons before they can return to ground state. • Chlorophyll is _____________ while the electron acceptor is _______________. but energy cannot disappear. electrons (ground state) (excited state) Without intervention, electron would fall back and release energy (as heat or fluorescence) oxidized reduced

14. Photosystem Assembly: In thylakoid, 3 parts: • Antenna complex = • Reaction center = only pair of chlorophyll a molecules which can donate e- to the e- acceptor • TWO TYPES OF PHOTOSYSTEMS: Differ in their location relative to specific proteins and e- acceptors. • Photosystem I: • Photosystem II: • Two routes for Electron Flow: Once excited, electrons flow: • Cyclic: • Non-Cyclic: 100’s of pigment molecules • Primary e- acceptor Absorbs far red (700nm) light best Absorbs red best (680nm) Photosystem I Photosystems I and II

15. During the light reactions, there are two possible routes for electron flow: • Cyclic Electron Flow: • Simpler pathway, involves only photosystem I: generates only ATP • Pigments absorb energy and channel it to: • P700 chlorophyll a’s electrons become excited, leave the molecule and are trapped by: • Electrons are passed along an ETC until returned to their ground state in P700: • What happens to the energy released by ETC? • This type of ATP production is called: cyclic & non-cyclic (no O2 or NADPH) the P700 reaction center primary e- acceptor They CYCLE back to their start point. Pumps H+ ions (into thylakoid from stroma) creates proton-motive force H+ flow through ATP synthase in thylakoid membrane ATP is made cyclic photophosphorylation

16. Cyclic Electron Flow

17. NonCyclic Electron Flow: • Involves both photosystem I and photosystem II • (SAME) Pigments absorb energy and channel it to: • (SAME) P700 chlorophyll a’s electrons become excited, leave the molecule and are trapped by: • Electrons are passed to NADP+ with H+ from water = • The e- that left the chlorophyll a must be replaced: • Light energy absorbed by P680 excites e- which are passed to the same ETC as cyclic electron flow until they reach P700 and replace the missing electrons: • The actual ATP production is the same as cyclic, but is called: • The P680 e- are replaced by e- from: • WATER was split into: the P700 reaction center primary e- acceptor NADPH (High energy e-) photosystem II does it the ETC makes ATP (same as cyclic flow) noncyclic photophosphorylation water H+ (joined NADP+) e- (replaces P680 e-) O (joins another O to be released as O2)

18. Noncyclic Electron Flow

19. Cyclic and Non-cyclic Electron Flow: Why have both??? • Cavin cycle requires more ________ than ____________ and ________________ • flow makes roughly _________ amounts. Cyclic flow makes the extra ___________ needed. • ATP Synthesis: Respiration vs. Photosynthesis • Both use chemiosmosis • Energy source is different: • Proton gradient (pH gradient): ATP NADPH noncyclic equal ATP • ATP synthase and many e- carriers are similar. food vs. light experiments from photosynthesis support chemiosmosis occurs in both

20. Calvin Cycle: Uses the ATP and NADPH made during light reactions to reduce carbon dioxide to sugar. (also called Light Independent Reactions) Actual product = also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GADP, GAP or PGAL Cyclic because 3 CO2 must go through the cycle to get one sugar – WHY? In addition to 3 CO2: Step 1: CO2 bonds to RuBP (5-carbon): Step 2: unstable 6-carbon compound splits Step 3: Each 3-carbon piece receives: Step 4: glyceraldehyde 3-phosphate (3-C sugar) entry compound RuBP is re-generated. Each CO2 provides one Carbon, G3P has 3 9 ATP and 6 NADPH are used RuBP carboxylase (rubisco) enzyme = very abundant protein in plants a Phos. group from ATP NADPH adds e- pair to each piece to reduce it to a 3-carbon sugar (G3P)

21. Calvin Cycle 3 3 Recycling Steps: For every ______ “turns of the cycle” ______ CO2’s enter, ______ G3P is gained for use and ______ RuBP’s are re-made. 3 1

22. Products of Photosynthesis: • Sugars typically leave the leaf as: • Most abundant organic molecule in plants: • Energy storage in plants = • Can be used for energy or carbon skeletons sucrose cellulose (structures) starch in chloroplasts, roots, tubers, and fruits

23. PHOTORESPIRATION: A process which reduces the sugar yield of photosynthesis On hot, dry days: Oxygen builds up in leaves and O2 competes with CO2 for the active site on When ______ is bonded in place of __________, the 2-carbon product is oxidized to _______ and ________ (in peroxisomes) This is bad because Believed to be: plants close stomata to conserve water CO2 decreases. Rubisco (enzyme) O2 CO2 CO2 H2O organic material is taken out of the Calvin cycle. evolutionary relic (no O2 on early Earth)

24. Methods of Minimizing Photorespiration: C4 Plants: Unlike typical (C3) Plants, C4 Plants use PEP: PEP binds CO2 in mesophyll (forms malate intermediate) and shuttles it to rubisco. PEP cannot bond to O2

25. CAM Plants (Crassulacean Acid Metabolism): Open stomates at night, take in CO2 and store it as organic acids in mesophyll vacuoles until morning.