CH10_2_ - Overview of Photosynthesis Nature of light Light...

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Unformatted text preview: Overview of Photosynthesis Nature of light Light reactions Photophosphorylation: light energy captured to make ATP and NADPH Non-cyclic (& cyclic) electron flow cyclic (& cyclic) flow Calvin Cycle ATP, NADPH, and CO2 used to make glucose Site of Photosynthesis Fig. 10-3 10- Bio 230, Summer 2010, Ch 10, Page 1 Structure & Location of Chloroplasts Leaf Cross section Mesophyll cells Chloroplast Structure Outer membrane Inner membrane Stroma Thylakoid membranes Grana stacks Thylakoid space Tracking Atoms Through Photosynthesis 6CO2 + 12H2O + light -> C6H12O6 + 6H2O + 6O2 glucose Fig. 10-4 10Bio 230, Summer 2010, Ch 10, Page 2 Overview of Photosynthesis Carbon Fixation Fixation Energy Storage GG- G+ G+ Energy Capture Fig. 10-5 10- Photosynthesis Two Stages Light Reactions Calvin cycle Products of light reactions (NADPH & ATP) used to fuel Calvin cycle Calvin cycle Bio 230, Summer 2010, Ch 10, Page 3 Photosynthesis Light Reactions - Thylakoids Solar Energy => Chemical Energy Energy Chemical Energy Light absorbed by chl drives transfer of electrons & hydrogen from water to NADP+ (reduction) NADP+ electron acceptor is closely related to NAD + ATP made through photophosphorylation Water is split, giving off O2 as a byproduct Photosynthesis Photosynthesis Calvin Cycle - Stroma CO2 fixed into organic compound Reduction of the fixed carbon to carbohydrate by adding electrons from NADPH Bio 230, Summer 2010, Ch 10, Page 4 NADP+ as Electron Shuttle NADP+ + 2H+ + 2e- NADPH + H+ NAD+ & NADH used in catabolic reactions NADP+ & NADPH used in anabolic reactions O-PO3 The Electromagnetic Spectrum C = 3x108 m/sec = 3x10 { C = speed of light (m/sec) = wavelength (m) = frequency (1/sec) Fig. 10-6 10- Light = energy - electromagnetic wave - photon, discrete particle - visible light drives photosynthesis - chlorophyll absorbs in blue & red Bio 230, Summer 2010, Ch 10, Page 5 Dual Nature of Light Electromagnetic wave Distance between crests of electromagnetic waves waves is called the wavelength Visible light (detectable by human eyes) has wavelengths of 380-750 nm 380- Photon Discrete particles with fixed quantities of Di fi energy energy E ≈ 1/wavelength (1/) hC/ E = h = hC/ (h = Planck’s Constant) Nature of Light Photon Energy Calculation E = h = hC/, h = 6.63 x 10-34 J·sec hC/ E.g., at 680 nm: = (3x108 m/sec)/6.8x10-7m) = 4.4x1014sec-1 E = (6.63x10-34J·sec)(4.4x1014sec-1) = 2.93x10-19J per photon = (2.93x10-19)(6.02x1023) = 176 KJ/mol = (176 KJ/mol)/(4.186 J/cal) = 42 Kcal/mol E.g., at 440 nm: E = 65 Kcal/mol Bio 230, Summer 2010, Ch 10, Page 6 Nature of Light In plants, chls are green because when illuminated by white light illuminated by white light Green light is reflected Red and blue light are absorbed by chlorophyll Pigments are molecules that absorb light are molecules that absorb light Each pigment will only absorb very specific photon with a certain wavelength Light and Chloroplasts - pigments = molecules that absorb light - each pigment absorbs specific wavelengths = green color of chls green color of chls Fig. 10-7 10- Bio 230, Summer 2010, Ch 10, Page 7 Pigment Absorption Spectra Fig. 10-9a 10- Action Spectrum O2 Release Fig. 10-9b 10- Bio 230, Summer 2010, Ch 10, Page 8 Englemann’s Experiment Fig. 10-9c 10- Chlorophyll Fig. 10-10 10- Bio 230, Summer 2010, Ch 10, Page 9 Photoexcitation of Isolated Chlorophyll Fig. 10-11 10- Lower energy Lower Higher Higher energy Higher Lower Photosystem Fig. 10-12 10- Bio 230, Summer 2010, Ch 10, Page 10 Photosystems Light harvesting complexes of the thylakoid membrane In thylakoid membrane, chlorophyll is th organized with proteins and other small organic molecules into photosystems Reaction center chlorophyll h Primary electron acceptor traps the highenergy electron before it can return to the ground state in the chl molecule Antenna pigments feed excitation energy to reaction center chlorophyll Photosystems Two photosystems centered about chlorophyll molecules Photosystem I, P700 P700 Photosystem II, P680 Work together in light reactions Bio 230, Summer 2010, Ch 10, Page 11 NonNon-Cyclic e- Flow Fig. 10-13 10- Note: 2 Photons make ½ O2 4 Photons make 1 O2 WSE Fig. 10-13a 10Bio 230, Summer 2010, Ch 10, Page 12 Photosystem I Note: 2 Photons + 2e- makes 1 NADPH 4 Photons + 4e- makes 2 NADPH Fig. 10-13b 10- Mechanical Analogy of Light Reactions Fig. 10-14 10- P680 P700 Bio 230, Summer 2010, Ch 10, Page 13 Fig. 10-17 10- Thylakoid 2 photons 2 photons 4 4 pH 5 2e- 6H+ 2 pH 8 6 pH = 3.0 VThy= +80 mV G = -6 kcal/mole/H+ Chemiosmosis Fig. 10-16 10- Bio 230, Summer 2010, Ch 10, Page 14 Efficiency of Light Rxns It takes 8 photons to make one O2 4 photons captured @ 50 kcal/mol each (create ½O2) ≈ -200 kcal/mol (exergonic) 2 ATPs and 1 NADPH made ATP NADPH ≈ +70 kcal/mol (endergonic) Efficiency ≈ 35% 3 x 1C = 3C 3 x P-6C-P = 18C+6P 3 x P-5C-P = 15C+6P 2Pi 6 x 3C-P = 18C+6P 3C 18C+6P 1Pi 6 x P-3C-P = 18C+12P Calvin Cycle Fig. 10-18 10- 5 x 3C-P = 15C+5P 6 x 3C-P = 18C+6P 1 x 3C-P = 3C+1P Bio 230, Summer 2010, Ch 10, Page 15 Efficiency of Calvin Cycle 1 G-3-P: G Cost: 9 ATP + 6 NADPH = 384 kcal/mol ATP NADPH 384 kcal/mol To make 2 G-3-P into glucose: G Cost: 2 ATP = 14.6 kcal/mol Total cost: 2 x 384 + 14.6 = 782 kcal/mol 1 Glucose Gl 686 kcal/mol Efficiency ≈ 88% Review of Photosynthesis Bio 230, Summer 2010, Ch 10, Page 16 ...
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This note was uploaded on 11/28/2011 for the course BIOL 230 taught by Professor J.breckler during the Spring '11 term at S.F. State.

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