ecture 16 Oct 7, 2005

Transcription

1 Lecture utline ecture 16 ct 7, 005 hotosynthesis 1 I. Reactions 1. Importance of Photosynthesis to all life on earth - primary producer, generates oxygen, ancient. What needs to be accomplished in photosynthesis 3. Structure of the chloroplast 3 functional spaces 4. ow light energy is harvested antenna complex, pigments, light spectrum - splitting of water, excitation of 5. What work is done with capture light energy - light reactions -noncyclic transport - and N - cyclic electron transport primarily, limit 6. ow and N power anabolic pathways - dark reactions the Calvin Cycle Photoauto autotrophstrophs Make their own food by light eterotrophs otrophs btain food from other sources ight nergy Solar Energy Input Photosynthesis is the ultimate energy source for almost all life on earth (Reflection/eat) Plant Biomass Production Photo Auto trophs G < 0 etero trophs eat Motion 3 Net Energy Absorbed And utilized Eat producers Net Energy (eat Motion) erbivore Biomass Production (eat) Carnivor mnivor 4

2 C xidized Carbon Input Photosynthesis Photosynthesis is a remarkably similar process at the molecular/cell biology level in a wide diversity of organisms Evolutionarily Related Process, or an Evolutionarily Conserved Process C Carbohydrate ancient Reduced Carbon utput Waste Product Basis for eterotroph Respiration 5 6 otosynthetic rganisms ) Multicellular algae Figure 10. Euglena Chlamydamonas Photosyntheic Protists (Eukaryotes) single cell (a) Plants (c) Unicellular protist 10 µm (d) Cyanobacteria 40 µm (e) Pruple sulfur bacteria Cyanobacteria blue-green algae Prokaryotes single cells stick together as mats 1.5 µm Vascular Plants Ferns Gymnosperms -conifers Angiosperms -monocots -dicots Non-Vascular Plants true algae bryophytes -liverworts -mosses Plants An entire Kingdom 7 Photosynthesis is comprised of TW Distinct Processes which occur simultaneously Energy Capture Processes Reactions (in most photosynthetic organisms) Energy Utilization Processes Dark Reactions Calvin Cycle NTE: NLY CCUR IN TE PRESENCE F Make use light to Make, N gas made as by-product Make Carbohydrate NEED and N 8

3 11 1 Reactions (energy capture) Chloroplast Figure 10.5 C LIGT REACTINS + P Interdependent N CALVIN CYCLE [C ] (sugar) Dark Reactions Calvin Cycle (energy utilization) 9 The organelle called the Chloroplast This organelle is the SITE of photosynthesis where ALL photosynthetic reactions occur Blue green algae (cyanobacteria) do not have internal membranes (they are prokaryotes!) but they themselves resemble chloroplasts The extensively folded plasma membrane of cyanobacteria lays the same role 10 as thylakoid membrane in chloroplasts Mesophyll Cell Leaf cross section Vein Chloroplast Mesophyll 5 µm Stomata C Figure 10.3 uter membrane Stroma Granum Intermembrane space Inner membrane

4 Chloroplasts -Contain their own DNA -Contain bacterial-like ribosomes -Believed derived from prokaryotic ancestor cyanobacterium = blue-green alga -Double membrane organelle defines three functional spaces 3 Central Players Space Stroma Membrane uterchlorplas Membrane 13 Membrane Intermembrane Space (transports things in and out o the chloroplast, but not centr to photosynthesis itself 14 troma - is where all the carbon fixation reactions ake place Space Stroma p 8.5 Spac is the transient energy storage shed for ions generated in the light reactions p5.5 Membran arvesting Complex - Antenna Complex - Water-Splitting Complex - Reaction Center Excitation Complex Membran Site of arvesting 15 16

5 Photosystem Antenna Complex - chlorophyll & accessory pigments STRMA Antenna -harvesting harvesting complexes Reaction center Primary election membrane Transfer of energy Special chlorophyll a molecules Pigment molecules Figure 10.1 TYLAKID SPACE (INTERIR F TYLAKID) Water Splitting Complex The Antenna Complex proteins which hold PIGMENTS Reflected light - the colors we see Pigments: Chlorophylls - absorb all but greens Chloroplast Reflected Xanthophylls - absorb all but yellows Carotenoids - absorb all but orange/reds Phycocyanin - absorb all but blue-green Absorbed light Granum Figure 10.7 Transmitted light 19 0

6 3 4 The electromagnetic spectrum the higher the energy, the shorter the wavelength Absorption Spectra of Antenna Pigments Chlorophyll a 10 5 nm 10 3 nm 1 nm 10 3 nm 10 6 nm Gamma rays X-rays UV Infrared Microwaves 1 m 10 6 nm 10 3 m Radio waves Absorption of light by chloroplast pigments Chlorophyll b Carotenoids Visible light igure nm Shorter wavelength Longer wavelength igher energy Lower energy 1 Figure 10.9 Wavelength of light (nm) Excitation of Chlorophyll by C 3 C in chlorophyll a in chlorophyll b Isolated chlorophyll when illuminated will fluoresce red, giving off light and heat Chlorophyll molecule Excited state Ground state eat (fluorescence) C C C 3 C C C C C Porphyrin ring: 3C C C C C 3 C N N C C Mg C 3C C N N C C C C C C 3 C C C C C C C C C C 3 -absorbing head of molecule note magnesium atom at center Figure ydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts: atoms not shown Blue light absorbed Red light Emitted With eat

7 Excited state Capture Water splitting complex (a protein in thylakoid membrane) Energy of election Figure A Chlorophyll molecule x x Ground state eat (fluorescence) Reaction Center Chlorophyll electron boosted to high energy level transferred to an electron transport chain need replacement electron 5 = Discard this, yuk These go to replace electron lost by chlorophy We ll save in the thylakoid space 6 troma hylakoid embrane PS II = (a gas) - PS I An pump p 8.5 N p P i ase 7 Key Players in the light reactions a. photosystem II: captures light energy boost to a higher energy level, splits water into and b. Electron transport pump: lets fall to lower energy level, uses energy to form gradient 8

8 c. another photosystem: photosystem I: captures light energy re- boosts to a higher energy level forms N *makes reducing equivalents* d. synthase ( ase): uses gradient to power synthesis 9 Produces [C N, ] (sugar), and oxygen Figure LIGT REACTINS N Primary e (PS II) CALVIN CYCLE 3 P Energy used to Form gradient ( Synthesis) Pq Electron transport chain 5 4 Cytochrome complex Non-Cyclic Electron Flow Primary Photosystem-I (PS I) Electron Transport chain Fd 7 e reductase PC P700 Photosystem I - Energy used 6 to make reducing equivalents (N ) 8 30 N + NAD + Non-Cyclic Electron Flow hotosystem I ight Energy can also be used to make gradient) N cyclic electron flow photosystem I is used primarily Primarily is produced Little produced Primary Fd Primary Fd Mill makes Pq Cytochrome complex reductase N N Pc igure Figure Photosystem I 3

9 Cyclic flow Electron Transport gradient ( synth) Photosystem I Reductase Photosystem II 33 Dependent Reactions Produce N And To power The Calvin Cycle Figure STRMA (Low concentration) TYLAKID SPACE (igh concentration) STRMA (Low concentration) LIGT 1 LIGT REACTR N 1 + membrane Pq CALVIN CYCLE [C ] (sugar) Cytochrome complex Pc synthase Photosystem I P Fd reductase N 34 To Calvin cycle Summary Next Time: the DARK Side The Calvin Cycle the independent reactions Photosynthesis ultimate source of energy for life n earth. Ancient Process highly conserved 3. membrane, Space, Stroma 4. Photosynthetic light reactions -capture energy from sunlight light harvesting pigments -use energy to split water -use energy to boost electron to high energy level (PS II) -electron transport lets electron fall to low energy state, energy used to make gradient () -electron re-boosted by light absorption to high energy state (PS I) - high energy electron used to reduce to N 5. Can vary relative amount of /N made by cyclic electron flow 36