Photosynthesis Chapter 6 PDF

Photophosphorylation Photophosphorylation: It is the conversion of ADP to ATP using the energy of sunlight by activation of PSII  It involves the splitting of the water molecule in oxygen and hydrogen protons (H+), a process known as photolysis.  Types of Phosphorylation:  Cyclic phosphorylation...

Photophosphorylation Photophosphorylation: It is the conversion of ADP to ATP using the energy of sunlight by activation of PSII  It involves the splitting of the water molecule in oxygen and hydrogen protons (H+), a process known as photolysis.  Types of Phosphorylation:  Cyclic phosphorylation and Noncyclic phosphorylation Q) Which photosystem performs cyclic phosphorylation? PSI Q) Which photosystem performs noncyclic phosphorylation? PSII • The movement of electrons during the formation of oxygen is called noncyclic photophosphorylation because electrons move in a linear path (H2O to NADP+) • Cyclic vs. noncyclic photophosphorylation: • Cyclic photophosphorylation is carried out by PSI independently of PSII. WHY? • Cyclic photophosphorylation is thought to provide additional ATP required for carbohydrate synthesis. Fig: 6.17 Cyclic photophosphorylation Absorption of light by PSI excites an electron, which is transferred to ferredoxin (step 1) then to cytochrome b 6f (step 2), then plastocyanin (step 3), and back to P700 (step 4). Fig 6.18: Cyclic photophosphorylation: From the absorption of light by PSI to the generation of ATP from a proton gradient In this process, protons are translocated by cytochrome b 6f to form a gradient utilized for ATP synthesis (step 5). Cyclic phosphorylation and Noncyclic phosphorylation Noncyclic phosphorylation • • • • • PSI and PSII are involved Source of electron is water Photolysis of water takes place NADPH is produced with ATP Oxygen is produced Cyclic phosphorylation • • • • • Fig taken from: https://www.sciencedirect.com/topics/agricultural-andbiological-sciences/photophosphorylation PSI is involved Source of electron is P700 Photolysis of water does not take place Only ATP is produced Oxygen is not produced Carbon Dioxide Fixation and the Synthesis of Carbohydrate • The movement of carbon in the cell can be followed during photosynthesis using [14C]O2 as a tracer. • Extracts of cells are then analyzed by autoradiography by identifying radiolabeled compounds compared to known standards. Fig 6.19: Chromatogram from algal cells after incubation with [14C]O2 showing accumulation of 3phosphoglycerate (PGA) © 2013 John Wiley & Sons, Inc. All rights reserved. How can the intake of CO2 produce carbohydrates? ? 1C 6C 1 C + 5C 6C Carbon dioxide + Ribulose bisphosphate Carbohydrate Calvin Cycle The cycle comprises three main parts: (1) carboxylation of Ribulose 1,5 bisphosphate (RuBP) to form (Phosphoglycerate) PGA (2) reduction of PGA to the level of a sugar (CH 2 O) by formation of glyceraldehyde 3-phosphate (GAP) using the NADPH and ATP produced in the light-dependent reactions (3) the regeneration of RuBP, which also requires ATP. Carbon Dioxide Fixation and the Synthesis of Carbohydrate • The condensation of RuBP and the splitting of the six-carbon molecule are catalyzed by one enzyme, ribulose bisphosphate carboxylase oxygenase know an Rubisco. • Rubisco is the most abundant protein on Earth, and has a very low turnover number. • Rubisco fixes ~3 molecules of CO2 per second. * 3-PGA is 3-phosphoglycerate Calvin Cycle • Carbon Fixation (light independent rxn) and takes place in the stroma (the inner space of chloroplast) • C3 plants (80% of plants on earth). • Occurs in the stroma. • Uses ATP and NADPH from light reaction. • Uses CO2. • To produce glucose: it uses 18 ATP and 12 NADPH. Calvin Cycle + Ribulose bisphosphate Short lived intermediate 3- Phosphoglycerate (3-PGA) -2 molecules Regeneration of CO2 acceptor (RuBP) Carbondioxide ATP 1, 3- Bisphosphoglycerate (BPG) NADPH NADP+ Pi Glyceraldehyde 3-phosphate (G3P) Make Glucose and other organic molecules Calvin Cycle 6 CO2 + 6 RuBP (1+5=6 carbons) (6+6 =36 carbons) 12 PGA (12-ATP) ATP 12 BPG (12-ATP) Pi NADP+ 12 G3P 36 carbon exists Calvin Cycle Regeneration of RuBP: Start with 36 carbons 1 3 2 4 6 5 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 From 12 G3P chains, two chains will form a Glucose molecule Mix and Match happens with the rest of the chains e.g: 22 23 24 25 26 27 28 36-6=30 10 G3P Glucose 29 30 4 6 5 9-5= 4 19 7 8 20 21 16 17 9 10 22 18 11 23 19 12 24 25 7-5= 2 13 14 15 9-5= 4 10 7-5= 2 1 2 3 4 5 5 5 20 9 8 7 Calvin Cycle • 6 carbons fixed with 6 RuBP chain and creates 12 G3P chains results in 36 carbons 6+6=12 G3P • Now it can create sugar molecule and RuBPs molecules. • These 12 G3Ps will form 2 glucose molecules (carbon use 6) –left over 30 • These 30 carbon will assemble and regenerate 6 RuBPs (6x5=30) • Total 10 G3P remains and form 30 carbons FIGURE 6.20 Converting CO 2 into carbohydrate https://www.youtube.com/watch?v=0UzMaoaXKaM Summary Slide Question Do you think process of photosynthesis is universal in all plants? What about plant live in very hot and dry habitat? Types of Photosynthesis: Carbohydrate synthesis in C3, C4 and CAM plants C3 plants C4 plants Wheat, Rye, Oats, Rice, Cotton, Sunflower Maize, Sugarcane, tropical grasses Named because of the Carbon molecule C3 produced during this process The C3 pathway is known as the Calvin cycle Reduction of PGA to GAP using NADPH and ATP and regeneration of RuBP Named because of the Carbon molecule C4 produced during this process C4 pathway involves the production of phosphoenolpyruvate (PEP), which then combines with CO2 to produce 4-carbon compounds oxaloacetate or malate. CAM plants Cacti, orchids Named because of Crassulacean acid metabolism CAM CAM pathway is a photosynthetic adaptation to periodic water supply growing in arid region. CAM plants close their stomata during the day and take up CO2 at night. It is like C4 plants and use that CO2 in morning. Chapter 6 (Quick Check) Q1) Draw and briefly explain the structure of a chloroplast Q2) What are the difference between photosynthesis and aerobic respiration? Q3) How do the light-independent reactions are different from the light dependent reactions? Q4) What are antenna pigments? What is the role in the photosynthesis role they play in photosynthesis? Q5) Explain the flow of electrons from Photosystem II to Photosystem I and how it reduces NADP. Q6) Define photophosphorylation? Q7) What is the difference between cyclic and noncyclic photophosphorylation. Q8) What is a Calvin cycle? Q9) Describe the major structural and biochemical differences between C3, C4 and CAM plants. How do these differences affect the ability of plants to grow in hot and dry climates?