BIOL 1411 1st Edition Lecture 14Outline of Last Lecture I. Photosynthesisa. Light Reactionsb. Light-dependent ReactionsOutline of Current Lecture I. Photosynthesisa. Calvin Cycleb. C4 photosynthesisc. CAMLectureUse of light Reaction Products to synthesize carbohydrates- Light-independent reactiono CO2 fixation and Calvin cycleo CO2 is reduced to carbohydrateso Enzymes in the stroma use the energy in ATP and NADPH to reduce CO2- Calvin and Benson used the 14C radioisotope to determine the sequence of reactions in CO2 fixationo They exposed Chlorella to 14CO2, then extracted the organic compounds and separated them by paper chromatography - The Calvin Cycleo CO2 is first added to an acceptor molecule 5-C RuBP; the 6-C compound immediately breaks down into two molecules of 3PGo The enzyme catalyzing the intermediate formation is rubisco- ribulose bio-phosphate carboxylase/ oxygenaseo Takes place in the stroma (not thylakoid lumen) - How is chemical energy used to synthesize carbohydrates?o G3P: Glyceraldehyde 3-phosphate is the product of the Calvin cycleo Most is recycled into RuBP; the rest is used to make sugars or stored starch- Sugar synthesiso CO2 enters leaf through stomatao Intercellular air spaceso CO2 mesophyll cells  chloroplastsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Water via veins - Photosynthetic carbon reductiono Carboxylation (carbon fixation)o Phosphorylation (uses ATP)o Reduction (uses NADPH)o Regeneration (uses ATP)o For each CO2, 3 ATP & 2 NADPH used - Keeping track…o 1x through cycle (1 CO2 incorporated) 2 NADPH used, 3 ATP usedo 3x (3 CO2 incorporated) 6 NADPH used, 9 ATP used 6 G3P generated (3 carbon molecules)- 5 G3P (5 x 3C) used to regenerate 3 ribulose bisphosphate (3 x 5C) 1 G3P is precursor to sugarso For 6C sugars, like glucose 6CO2 are incorporated- photochemical reaction stimulate the calvin cycleo the calvin cycle is not light-dependent, but is stimulated by light protons pumped form stroma into thylakoids increase the pH which favors the activation of Ribisco elctron flow from photosystem I reduces disulfide bonds to activate CalvinCylce enzymes- Photosynthesis: conceptso Light energy is used to move elctronso ATPo NADPHo E- patho Cyclic electron flow provides extra ATP’s- Photorespirationo Ribulose bisphosphate + CO2  3PG First step in Calvin cycleo Catalyzed by enzyme Most abundant enzyme on earth Bibulose bisphosphate carboxylase (rubisco) Binds ribuose bisphosphate and CO2 Active site also binds O2 Wastefulo Rubisco bind O2 catalyzes an oxygenation reaction Sugar is burned (O2 added) But, no ATP is generatued: wasteful “photo” occurs in light “respiration” uses O2, gives off CO2o Conditions that favor photorespiration Sunny, dry, windy Plant closes stomata to conserve water Photosynthesis continues: CO2 is depleted, O2 builds up Up to 50% loss of sugars o Why does this wasteful process occur? Evolutionary remnant Primitive Earth: no O2 in atmosphere  No selection A locked in defect o Adaptations to avoid PR Protect rubisco from low CO2, high O2 Calvin cycle is not affected Take extra steps, use extra energy Initial carboxylation- Spatial separation: C4 Photosynthesis- Temporal separation: CAM C4, CAM: geographically restricted- Use extra energy- Found in sunny localeso C4 photosynthesis Initial product: 4 carbon molecule 2 photosynthetic cell type- Bundle sheath cells- Mesophyll cells Both have chloroplasts different enzymes in 2 cell types CORN!o CAM Crassulacean acid metabolism- Crassulacea: family of deser-dwelling secculents Open stomata at night, rather than day- Reuces transpiration - Gas exchange at night: CO2 in, O2 out- Initial carboxylation yields organic acido How does photosynthesis interact with other pathways? Photosynthesis and respiration are closely linked through Calvin cycle G3P is important- Some takes part in glycolysis and cellular respiration for energy, or can make other compounds- Some is involved in gluconeogenesis, the reverse of glycolysis, supplying nonphotosynthestic parts o Energy Loss in Photosynthesis Wavelengths of light not part of absorbed due to plant structure Inefficiency of light reactions converting light to chemical energy Inefficiency of CO2 fixation