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Canada (510,633)
BIOC13H3 (52)
Daman Bawa (12)
Lecture 9

BIOC13Winter2013 Lecture 9 Notes.docx

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Department
Biological Sciences
Course
BIOC13H3
Professor
Daman Bawa
Semester
Winter

Description
BIOC13Winter2013 Lecture 9 Photosynthesis Part IThe light reactions Overview o Process that traps light energy and uses it in the synthesis of carbs o Phototrophs organisms capable of photosynthesisplants different groups of bacteria algae diatoms o Solar energy is captured in form of ATP and reduced coenzymes o Chemical energy is used to convert atmospheric carbon dioxide and water into carbohudrates o Main source of oxygen o Oxidation of water is unfavourable so driven by light energy o COHOCHOO 2222o Electrosn from oxidation pass through an electron transport system similar to the one in mitochondria o 6 HO6 COCHO6 O 2261262o delta G is 2969kJmol which is supplied by conversion of light energy to chemical energy in the form of ATP and NADPH o light reactions light dependentprotonosfrom water are used in the chemiosmotic synthesis of ATP electrons from water reduce NADP to NADPH o light dependent realease oxygen o HOADPPNADPlight OATPNADPHH 2i2o Dark reactions light independentCalvin cycle reactionsNAPD and ATP used to reduce CO2 and incorporate into 3 carbon precursors of cabs o Do not directly depend on light but on the sypply of NADPH and ATP o Occur simultaneously with light reactionso COATPNADPHHCHOADPPNADP22i The Chloroplast oo enclosed by double membrane that is highly permeable to CO2 and selectively permeable to other metabolites o thylakoid compartmenthighly folded internl membrane networksight of light reactions translocation of H across this compartment creates proton motive force that derives ATP synthesis o stromamatrix surrounding the thylakoid compartment contains soluble enzymes that catalyze the reduction of carbon dioxide to carbohydrates contains DNA RNA and protein synthesis machinery o granumflattened thylakoids arranced in stacks interconnected by unstacker stroma lamellaeChlorophyll o thylakoid membrane contains protein bound pigment molecules that capture lightphotoreceptors o some of the pigments are arranged within functional units called photosystemso cholorophylls are the most abundant pigments specifically oriented in the thylakoid membraneo tetrapyrrole ring chlorinsimilar to heme but containd Mg2 and an additional 5C ring hydrophilic light absorbing network alternating single and double bonds o hydrophobic phytol side chainanchors chlorophyll in the membrane20C alcohol esterified to an aicd side chaino there are different types of chlorophyll o chlorophyll a and chlorophyll b are found in vascular plants with chl a being 23 times more abundanto bacteriochlorophyll a NChl a and Bacteriochlorophyll b are the major pigments in photosynthetic bacteria o these chlorophylls differ from heme and each other in degree of saturation of rings II and IV and in the substituents of Rings I II and IV o the structure affects the absorption spectra of these molecules o strong absorption in visible light spectrum Accessory pigments o pigments other than chlorophyll that are present in photosynthetic membraneso contain a series of single and double bonds that allows for light absorption in regions where chlorophylls dont absorb light o 2 main types o carotenoidsyellow to brown present in all phototrophs o phycobilinsphycoerythrin red phycocyanin blue present in some algae and cyanobacteria1
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