Lecture 11 Photosynthesis Chapter 9 Photosynthesis capturing light energy pp 193 206 Outline Introduction Light Photons Absorption Outline Chloroplast structure and photosynthetic pigments Photosynthesis Light dependent reactions Non cyclic electron transport and Cyclic electron transport ATP synthesis by chemiosmosis Carbon fixation Photosynthetic organism almost all plants are photosynthetic autotrophs as are some bacteria and protists Introduction Photosynthesis and the ecosys tem photosynthesis is the first step in the flow of energy through most of the living world primary produces primary consumer secondary consumer tertiary consumer climate change water availability for agriculture land use growth of human population Interdependence of photosynthesis and respi ration photosynthesis takes place in the chloroplasts Nature of light The Electromagnetic Spectrum electromagnetic energy wave wavelength particle photons a discrete packet of energy is inversely proportional to wave light energy length Interactions Between Light and Atoms or Mole cules e that are excited to a higher energy level may return to a ground state and the energy released fluorescence Chloroplast where photosynthesis happens cynobacteria all able to go through photosynthesis but have chloroplasts chlorophyll pigment in chloroplasts structure outer and inner membrane stroma thylakoid thylakoid membrane more surface for e transport complexes and ATP synthases in the folding of thylakoid membrane the cell will have more surface increase amount of membrane in the cell granum granna Endosymbiosis Theory explains the origin chloroplasts and mitochondria in eukaryotic prokaryotic bacteria was engulfed by a plasma membrane mitochondria and chloroplasts are explained through this theory chloroplasts have their own DNA Photosynthetic pigments pigments substances that absorb visible When light meets matter the light is a reflected b transmitted c absorbed wavelengths that are not absorbed are reflected or transmitted Chlorophyll in a chloroplast you have a thylakoid in the thylakoid membrane their is chlorophyll resembles lipid bi layer chemical structure chlorophyll molecule a a porphyrin ring that absorbs light energy b hydrocarbon side chain c magnesium d non polar part of chain is used to anchor hydrocarbon side chains chlorophyll a and chlorophyll b have a different absorption level Photosynthetic Pigment green chlorophyll a Ch a pigment that initiates light dependent reactions of photosynthesis Need a wide range of accessory pigments to capture different wavelengths of light chlorophyll b accessory pigment different absorption that Ch a yellowish and green have different functional group carotenoids a yellow and orange pigments b absorb different wavelengths of light than chlorophyll c expand the spectrum of light used in photosynthesis Comparison of action and absorption spectra absorption spectrum the spectrum of light waves absorbed by a particular pigment action spectrum rate of photosynthesis for each specific wavelength having more than one pigment will allow for a multiple of wavelengths chlorophyll a absorbs red and blue light and reflects green light Light Reactions happen in thylakoid reactions make ATP and NADPH H20 is split O2 is released Overview of photosynthesis 1 Calvin Cycle occurs in stroma uses ATP and NADPHy form light reactions produce carbohydrates from CO2 electron carrier in photosynthesis is NADPH Photosynthesis redox reactions Photosystem Structure Photosystem I PI and II PII include antenna complexes Ch a b and accessory pig ments PI absorption of 700 nm PII absorption of 680 nm the function is for light energy to be converted to chemical energy in the reaction center by e transfer Noncyclic Electron Transport One way flow of e The energy of the sun is going to impact the system and move one electron out in the orbital this electron is captured by elec tron carrier b c final acceptor in the electron transport chain is ferredoxin the electron lost in PI is used to make NADPH Photolysis of water releases oxygen light splits water indirectly by causing P680 oxida NAPH and ATP production of energy for every 2 electrons passed to the electron transport cain 2 ATP and 1 NADPH are pro tion duced in the Z scheme only uses one system Cyclic Electron transport The Calvin Cycle production of carbohydrates takes place in the stroma a divided into three phases co2 uptake carbon dioxide reacts with 5 carbon compound ribulose bisphosphate RuBP forming phosphoglycerate PGA catalyzed by rubisco carbon reduction PGA is phosphorylated G3P using ATP and NADPH from light dependent reactions RuBP regeneration G3P molecules regenerate RuBP which is used to restart the cycle