photosynthesis
DESCRIPTION
Photosynthesis. The process of converting energy from sunlight to energy in chemical bonds. 6CO 2 + 6H 2 O + light C 6 H 12 O 6 + 6O 2 Light absorbing pigments: Chlorophyll a (P 680 and P 700 ) Chlorophyll b Carotenoids (red, orange, or yellow) - PowerPoint PPT PresentationTRANSCRIPT
Photosynthesis
• The process of converting energy from sunlight to energy in chemical bonds.
• 6CO2 + 6H2O + light C6H12O6 + 6O2
• Light absorbing pigments:– Chlorophyll a (P680 and P700)– Chlorophyll b– Carotenoids (red, orange, or yellow)
• Photosystems: PS I [P700 ] and PS II [P680 ]
Noncyclic Photophosphorylation
• Process of making ATP from ADP + Pi using energy derived from light
• 7 steps:1) Photosystem II2) Primary electron acceptor3) Electron transport chain4) Phosphorylation5) Photosystem I6) NADPH7) Photolysis
Noncyclic Photophosphorylation
• Summary– Takes light energy and electrons from H2O to
make the energy-rich molecules ATP and NADPH
– Light-dependent reactions, or light reactions
Cyclic Photophosphorylation
• Electrons from PS I are “recycled”
• Electrons from PS I join with the Electron Transport Chain and generate ATP, returning to PS I
Calvin-Benson Cycle(Dark Reactions)
• Fixes CO2
• Takes inorganic CO2 and incorporates it into an organic molecule that can be used in biological systems
• Goal: produce a single molecule of glucose (C6H12O6)
• Must repeat 6 times, using 6 CO2 molecules
Calvin-Benson Cycle(Dark Reactions)
• Carboxylation: 6 CO2 combine with Ru BP to produce 12 PGA– Enzyme: RuBP carboxylase, or Ribisco
• Catalysis the rxn CO2 and RuBP (ribulose biphosphate)
• Reduction: 12 ATP and 12 NADPH are used to convert 12 PGA to 12 PGAL
• Regeneration: 6 ATP are used to convert 10 PGAL to 6 RuBP
• Carbohydrate synthesis
Calvin-Benson Cycle(Dark Reactions)
• Summary– 6CO2 + 18 ATP + 12 NADPH
18 ADP + 18 Pi + 12 NADP+ + 1 glucose
Chloroplast
• Structure– Outer membrane– Inner membrane– Stroma
• Enzymes for the Dark Rxns
– Thylakoid• Contain the light-absorbing pigments and enzymes for the
light rxns
– Thylakoid compartment– Granum
Chemiosmotic Theory
• Describes the mechanism by which ADP is phosphorylated to ATP
• Steps:
1) H+ ions (protons) accumulate inside the thylakoids
2) A pH and electrical gradient (electrochemical) across the thylakoid membrane is created
3) ATP synthase generate ATP
Photorespiration
• Ribisco has the ability to fix O2, as well as carbon dioxide
• Problems:– Decrease efficiency of CO2 fixation– Products formed react with RuBP do not lead to
useful, energy-rich molecules• Peroxisomes breakdown these products
C4 Photosynthesis
• PEP (phosphoenolpyruvate)
• OAA (oxaloacetate)
• PEP carbooxylase
• Malate
• Bundle sheath cells
• Stomata are partially open during the day
• Plants found in hot, dry climates
• Sugar cane and crab grasses
CAM Photosynthesis
• PEP carboxylase
• OAA
• Malic acid
• Stomata are closed during the day and OPEN at night
• Vacuole
• Plants found in hot, dry climates with cool nights (deserts)