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Chapter 4.2 – 4.3 Building sugar photosynthesis Kevin Bleier Milton HS, GA Who does photosynthesis? Overview – summary equation sunlight, enzymes 6 CO2 + 6 H2O C6H12O6 + 6 O2 • Once again, just a summary • Photosynthesis a factory of enzymes just like respiration Overview of photosynthesis • 2 broad steps: 1) Light reactions – trap sunlight energy, transform into ATP / electron energy (H2O consumed, O2 produced) 2) Calvin cycle – use ATP / electron energy to power formation of sugar (CO2 consumed, C6H12O6 produced) Overview of photosynthesis thylakoid membrane Overview of photosynthesis thylakoid membrane Overview of photosynthesis Light reactions – capturing light • Evolution toward usage of visible light – the wavelengths that enter the atmosphere the most Multiple pigments capture light Measuring light absorption • Spectrophotometer • Green light NOT absorbed • Blue, red light absorbed Multiple pigments capture light Chlorophyll after absorbing light • Chlorophyll energizes electrons within it • High energy electrons stolen from chlorophyll, sent to electron transport chain • Water cut up to give new low-energy e-s to chlorophyll Next step = electron transport chain • Similar steps to respiration • High energy e-s help ETC pump H+ to one side • H+ come back in through ATP synthase ATP production in light reactions Next step – another photosystem • e-s fill a hole in another chlorophyll molecule, where e-s have been excited again What happens with these e-s? • Captured by NADP+ to make NADPH Summary of light reactions • Purpose: generate ATP and NADPH energy needed to power production of sugar • Using sunlight energy to excite electrons, then converting energy of electrons into ATP and NADPH energy • Electrons do NOT come from sunlight, they come from water Summary of light reactions • In: H2O, ADP, NADP+ • Out: O2, ATP, NADPH Photosynthesis: Calvin cycle • CO2 gas fixed into sugars already there • ATP and NADPH spent to convert into other sugars • Some sugar can leave the cycle, others stay to fix more CO2 Photosynthesis summary