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Photosynthesis

Photosynthesis. Bio 391 – Ch4 How Exactly is Sunlight captured and converted into Food?. What are autotrophs?. Obtains energy from nonliving sources Two types Photoautotrophs Photosynthesis Sun energy converts CO 2 into sugars

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Photosynthesis

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  1. Photosynthesis Bio 391 – Ch4 How Exactly is Sunlight captured and converted into Food?

  2. What are autotrophs? • Obtains energy from nonliving sources • Two types • Photoautotrophs • Photosynthesis • Sun energy converts CO2 into sugars • Enzymes convert sugars into amino acids and other needed compounds • Chemoautotrophs • Specialized bacteria • No sunlight – use energy of inorganic substances (Fe, S, etc.)

  3. Electromagnetic Spectrum • Wide range of energy types – travels in waves – energy is defined by their wavelength • λ = wavelength = distance between two adjacent wave crests or wave troughs • Visible Light • Very small section of the electromagnetic spectrum • ROYGBIV

  4. Rainbows are separated white light* white reflects all light* black absorbs all light* color seen is that color reflected

  5. Chloroplasts • Structure • Thylakoids • Highly folded inner membrane • surface area • Holds pigments • Granum • Stack of thylakoid membranes • Stroma • Liquid between thylakoid and outer membrane of chloroplast • Have their own DNA & RNA

  6. Chlorophyll & Accessory Pigments • Pigments = light absorbing molecules • Found on the thylakoid membrane • Chlorophyll • Two types – “a” and “b” • Absorbs violet-blue and orange-red colors • ~ 350-500 nm & 650-700 nm • Reflects green  plants have green color • Accessory Pigments • Absorb other colors of light and transfer Σ to chlorophyll-a • Most noticeable in the fall months • EX: carotenoids

  7. Absorption Spectrums of Pigments

  8. Photosynthesis Simplified • Can be broken down into two steps: • Light Reactions • Pigments in thylakoids absorb light • Light converted into chemical energy • Calvin Cycle (a.k.a. “Dark Reactions”) • Chemical energy from light reactions used to make 3 carbon sugars from CO2 • Used to make more complex sugars or other biochemical molecules • Overall Reaction • 6CO2 + 6H2O C6H12O6 + 6O2

  9. Light Dependent Reactions • Broken into Photosystem II and Photosystem I • Reactants: • light, water • Use: • ADP and Pi to make ATP • NADP+ to make NADPH (similar to NAD+/NADH) • Happens on the thylakoid membrane

  10. Light Dependent Reactions • Photosystem II • Light hits the chlorophyll molecules and excites them – releasing two high energy electrons • Electrons are used to create a H+ gradient across the thylakoid membrane • This gradient drives the formation of ATP (similar process to the ETC in respiration) • Photophosphorylation

  11. Light Dependent Reactions • Photosystem I • Light hits the chlorophyll molecules and excites them – releasing two high energy electrons • Electrons from Photosystem II replace the electrons that leave chlorophyll molecule • Electrons are captured by NADP+ to make NADPH

  12. Light Dependent Reactions • ATP and NADPH are used in the light independent reactions • How are electrons from Photosystem II replaced? • Water is split • O2 – waste product – released by the plant • Electrons – go into chlorophyll to replace lost e’s • H+ - used to make gradient to help make ATP

  13. LIGHT DEPENDENT REACTIONS

  14. Cyclic v. Noncyclic Photophosphorylation • Cyclic – photosystem I only – electrons are recycled (use no NAPDH) • Chemiosmosis – process of using proton movement to join ADP and Pi • http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter39/cyclic_and_noncyclic_photophosphorylation.html • Simple vs. Complex Autotrophs • Generates ATP but not NADPH. Why?

  15. Light Independent Reactions • Also called the Calvin Cycle • Reactants: • ATP, NADPH, and CO2 • Use: • ATP to make ADP and Pi • NADPH to make NADP+ • Sugars are created • Happens in the stroma

  16. Calvin Cycle • Keys to understanding…. • It’s all about rearrangement of carbon atoms • CO2 enters cycle by attaching to RuBP • RuBP is a 5-carbon molecule • Similar to Acetyl CoA entering Krebs cycle • Creates 2 PGA • PGA is a 3-carbon molecule • PGA turns into PGAL • PGAL is a PGA molecule that has been energized by the ATP and NADPH

  17. Calvin Cycle Summary • Each turn fixes 1 CO2 to a RuBP • Rubisco • Enzyme that catalyzes CO2 fixation • Activated by light thus Calvin cycle requires some level of light to occur • Can bind O2 if present • 3 turns = 1 PGAL • “C3 plants” – those that fix 3 CO2 into 1 PGAL

  18. Calvin Cycle Summary RuBP unstable 6C sugar (5C) CO2 PGA PGA (3C) (3C) ATP ATP 5 PGAL to regenerate PGAL (3C) NADPH NADPH 1 PGAL released for growth PGAL (3C) 6 PGAL 3x

  19. PGAL

  20. Light Reactionhttp://vcell.ndsu.edu/animations/photosynthesis/movie.htm Calvin-Benson Cycle http://www.youtube.com/watch?v=mHU27qYJNU0

  21. Light- dependent reactions Calvin cycle Energy from sunlight Thylakoid membranes ATP Stroma NADPH High-energy sugars ATP NADPH O2 Chloroplasts Concept Map Section 8-3 Photosynthesis includes takes place in uses use take place in to produce to produce of

  22. Factors Effecting the Rate of Photosynthesis

  23. More light = higher rate Reaches saturation point Enzymes of light reaction going as fast as possible Higher than saturation point  PS declines Chlorophyll accumulates light faster than it can transfer it to ETS Extra energy goes to oxygen producing OH- when reaction w/H2O OH- or H2O2 damages chloroplasts Light Intensity PHOTOINHIBITION

  24. Similar to light intensity Hits a saturation point Does not decline after saturation CO2 Concentration

  25. Optimal temperature range If too high… Proteins denature If too low… Molecular movement is slower High Temps = cause stomata to close Prevents water loss Increases photorespiration C4 and CAM adaptations Temperature A metabolic pathway in plants that consumes oxygen, produces carbon dioxide, generates no ATP, and reduces photosynthesis

  26. O2 Concentration / Photorespiration • REMEMBER  Rubisco binds CO2 and O2 equally as well • Molecular shapes are similar • Halves productivity of PGA • Carbon fixation = 2 PGA • Photorespiration = 1 PGA • Glycolate = toxic to plant • Benefits of photorespiration? • Occurs when stomata close • Dry and hot • Evolutionary of C4 and CAM plants • Still makes some CO2 and thus some sugars

  27. C3 vs C4 vs CAM http://wc.pima.edu/~bfiero/tucsonecology/plants/plants_photosynthesis.htm

  28. Leaf Anatomy – C3 vs. C4 • C3 plants • CO2 pulled through stomata and immediately goes to mesophyll cells to complete photosynthesis • Called C3 because it makes PGA (3-Carbon molecule) • Stomata open during day • Efficient in cool and moist envir. • C4 plants • CO2 pulled through stomata and immediately goes to mesophyll cells then to the bundle sheath cells to complete photosynthesis • Called C4 because it makes a 4-carbon molecule first (using PEP carboxylase • Stomata open during day • Efficient in higher temps and higher light intensity

  29. Reducing Photorespriation:CAM plants • CAM plants • Crassulacean Acid Metabolism • CO2 pulled through stomata and stored as an acid. During the day, stomata close, CO2 is released, then the cell goes through the Calvin cycle • Stomata open during night • Close during the day to prevent water loss • Efficient in extremely hot and dry environments

  30. Photosynthesis Song 1: The Light Reactions Song Photosynthesis Song 2: The Calvin Cycle

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