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Lecture 6

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Western University
Biology 1002B
Denis Maxwell

Lecture 6: Energy Transformation I 1. What defines a catabolic versus an anabolic pathway - give some examples of each.  Catabolic pathway of cellular respiration o Energy is released by the breakdown of complex molecules to simpler compounds  Anabolic pathway or biosynthetic pathways of photosynthesis and synthesis of macromolecules o Consume energy (overall sum, +∆G) to build complicated molecules from simpler ones 2. How is the structure of ATP linked to the fact that its hydrolysis is strongly exergonic?  ATP + H 2  ADP + P i  Both products carry a negative charge - repulsion between ionic products favours hydrolysis  Release of phosphate allows greater opportunity for hydration (solvation) - energetically favoured state  Orthophosphate group can exist in a wide variety of resonance forms - release of this increases disorder 3. Photosynthesis  50% photosynthesis is aquatic at most at the poles (cold) o Highest amounts of chlorophyll not due to temperature o Water in the poles are nutrient rich  Anabolic endergonic process of converting light to energy  Light dependent reduction of CO 2  Reducing CO t2 sugar and oxidizing H 2 to O 2redox coupling) o + linear relationship of free energy vs progress of reaction o No free energy in CO but lots in sugar due to CH bonds not wanting H 2  Not only a eukaryotic process o Bacteria just doesn’t have a chloroplast o Outer membrane is like the plasma membrane of a photosynthetic bacteria o Thylakoid just sits in the cytosol 4. Structure of chloroplast  Outer and inner membrane  Stroma - Aqueous environment with lots of enzymes  Thylakoid membrane - photochemistry, light reactions  Thylakoid lumen - Compartment of thylakoid 5. Source of electrons and products of electron transport  NADPH gives source of electrons  Products: NADPH, ATP 6. Structure of photosynthetic electron transport  Photosystem II - Chlorophyll P680 o PQ needs to be neutral to stay in membrane  Picks up e and becomes ‘–’ charged but pick up H from stroma and dump it into lumen  Electrochemical gradient used to do work (chemiosmosis: diffuse ions across membrane)  pH of lumen becomes very low compared to the stroma o too fluid – PQ fall apart and leave o too rigid – PQ have problems moving rapidly  Photosystem II to cytochrome then to plastocyanin then to photosystem I  Photosystem I o Electron from P680 goes to reduce chlorophyll P700  P680 gets electron from splitting water to make oxygen on lumen side + - o Electron excited eventually go to reduce NADP + 2e  NADPH  lumen is
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