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118-chapter Biology 10 photosynthesis: Autotrophs: make own food Heterotrophs: depend on others for food. 2 distinct rxns: 1) light rxn: produce O2 from H2O. 2) light-independent rxn: -CO2 reduced to make carbonhydrate even in the dark. -electrons are released in the light rxn and transfer NADP+ to form NADPH. (an electron carrier similar to NADH cellular respiration) -ATP is also made by light rxn. -the NADPH/ ATP are used in the reduction of CO2 in the Calvin Cycle. Where does photosynthesis occur? -photosynthesis occurs in the chloroplast of green plant -chloroplast like mitochondria, 1) grow/divide independently 2) double membrane 3) contain chloroplast +DNA 4) contain everything required for photosynthesis. -inside chloroplast are vesicle like structures: thylakoids. Lumen: space inside a thylakoid Stroma: fluid fill space b/tw thylakoid and inner membrane. The thylakoid membrane of choloplast contains the pigment chlorophyll. *chlorophyll absorbs blue and red light, transmit green light. -the electron-magnetic spectrum is the range of wavelenth of electromagnetic radiation. -shorter wavelength--higher energy (blue/violet) -longer wavelength--lower energy (red). How does chlorophyll capture light energy? -packets of light are called photons has specific amount of energy -chlorophyll can absorb photons. The major leave pigments: Chlorophyll (A and B): absorbs red/blue light, transmit green light Carotenoids: absorbs blue and green light, transmit yellow, orange/red light. 1) -absorb wavelength of light not absorbed by chlorophyll and pass on to chlorophyll (transfer the energy) 2) expand the range of light. 3) also stabilizes the free radical produced by electromagnetic radiation, protecting chlorophyll from degradation. Flavonoids: protects chlorophyll and other plant molecules from destructive radiation by absorbing high-energy ultraviolet light. The structure of chlorophyll : 1) chlorophyll (a and b), similar structure, differ absorption spectrum. 2) ring structure: absorb light energy. 3) long isoprene tail anchors chlorophyll in the thykoid membrane. * when light is absorb by the ring structure electron enters excited state contain more potential energy. How do chlorophyll molecules in leaves work?? photo-systems are the light harvesting unites of the thylakoid membranes each has a light gathering antenna complex consisting of a cluster of a few hundred chlorophy a,b and carotenoid moelecules. -antenna complex-> when a red/ blue photo strikes a pigment molecule, energy is absorbed. Electron in the pigment is excited. * the energy (but not the electron itself) is passed along to a nearby chlorophyll molecule. Exciting another electron in that chlorophyll, energy is transmitting from chlorophyll to chlorophyll until it reaches the reaction center. At the rxn center( photosytem 1and II) -transfer energy excite electron in the rxn center -excited electron in the rxn passed to another electron acceptor in the rxn center -this results in an transformation of electronmagnetic energy into chemical energy. BOTH systems work together to produce an enhancement effect: the photosynthetic rate is more than double than of either system's rate along. Photosystem II: -the antenna complex transmit energy to RXN center -high energy electron is donated to and reduces phenophytin (a molecule, similar to chlorophyll that lack Mg in the head region) Electron Transport Chain( ETC) -electron pass from phenphytin to an ETC cytochrome containing and guinones (like in the mitochondria) Photosystem II and cytochrome complex: are locaed in the thykoid membrane of the chloroplast. -plastoquinoe (PQ) shuttle electron from phenphytin across the thylakoid membrane to a cytochrome complex -PQ also carries: proton, across Thykoid membrane. -creating proton-motive force -ATP synthases use the proton-motive force to phosphorylate ADP -ATP synthase and the process similar to mitochandria. -photophosphorylation : the capture of light energy by photosystem II to produce ATP. Where does Psystem II get the electron it lost? Psystem ii obtains electron by oxidizing H2O. Oxygenic photosynthesis: Ps II splits H2O to replace its lost electron and produce O2. 2H2 4H+ + 4E- + O2. Ps ii IS THE ONLY KNOWN PROTEIN THAT OXIDIZE WATER. Photosystem I (ps1) - reduces NADP+ NADPH. Excited electron from the rxn center of ps1, pass down the ETC to ferredoxin - NADP+ Raductase: transfer a proton and two electrons from ferredoxin to NADP+ form NADPH. Where does PS1 got the E-? -FROM PS2. -both systems work together in a Z-scheme (Explains the enhancement effect) -plastocyanin (PC) takes an electron from cytochrome complex. -carries it back across the Thykoid membrane to PS1. -so ps2 is physically linked to ps1 How is CO2 reduced to produce Glucose? -rxn that produce surgar from CO2 are light-independent. -calvin cycle rxn occur in chloroplast stroma. -require ATP/NADPH produced by the light dependent rxns. Calvin Cycle: reduce CO2 to produce 3-phosphoglycernate produce glucose. -carbon fixation : the attachment of Co2 to an organic compound 3 steps: 1) Fixation : 5 carbon ribulose biphosphate (RuBP) reacts with CO2. To produce 6 carbon compound - 2 molecules of 3-phosphoglycernate. 2) Reduction: 3-phosphoglycernate are phosphorylated by ATP/ reduced by NADPH. To produce G3P (glyceraldehyde-3 phosphate) Some G3P is drawn off to make glucose. 3) Regeneration : the remaining G3P is used in Rxn that regenrate RuBP. The cycle uses lots of ATP and NADPH. *Stomata: leaf structure where gas exchange occurs. An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle. The light reactions use solar energy to make ATP and NADPH, which function as chemical energy and reducing power, respectively, in the Calvin cycle. (notice that in contrast to ATP generated by cellular respiration, ATP produced in the light reactions of photosynthesis is usually dedicated to a single kind of cellular work, driving the Calvin Cycle). The Calvin Cycle incorporates CO2 into organic molecules. Thylakoid membranes, especially those of grana, are the sites of the light reactions, whereas the Calvin cycle occurs in the stroma. The logistics of chemiosmosis in mitochondria and chloroplasts: The inner membrane of the mitochondrion pumps protons (H+) from the matrix into the inter-membrane space (high H+concentration) . ATP is made on the matrix side (low H+ concentration) of the membrane as hydrogen ions diffuse through ATP synthase complexes. In chloroplasts, the thylakoid membrane pumps protons from the stroma into the thylakoid compartment. As the hydrogen ions leak back across the membrane through the ATP synthase, phosphorylation of ADP occurs on the stroma side of the membrane Results: Photosynthesis : uses light and water produces O2, give ATP and NADPH to - Calvin Cycle: uses CO2 to produce Sugar, meanwhile oxidizes ATP and NADPH to NADP+ and ADP.

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