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Lecture 9

BIO204 Lecture 9 (CH9)

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University of Toronto Mississauga
Sanja Hinic- Frlog

9 (CH9) October-14-13 4:31 PM Flow of energy in biological systems – Organisms transform energy and fuel metabolism Flow of energy in biological systems – Photosynthetic reaction is the reverse of cellular respiration 6 CO + 6 H O C H O + 6 O 2 2 6 12 6 2 (+ light energy) (+ ATP + release of heat) Other carbohydrates,fats, and proteins are also used as fuel for cellular respiration, but glucose is starting point for glycolysis Key Concepts - Respiration • Endergonic reactions (requiring energy) are needed for cellular metabolism • They are paired with exergonic reactions (releasing energy) involving ATP • Cellular respiration produces ATP from moleculeswith high potential energy – e.g. glucose • Glucose processing has four components: (1) Glycolysis (2) Pyruvateprocessing (3) Krebs cycle (Citric acid cycle or Tricarboxylic acid cycle) (4) Electron transport coupled with oxidative phosphorylation • Fermentation– alternativepathways ○ Glycolysiscontinues when lack of an electron acceptor shuts down electron transport chains • Respiration and fermentationare carefully regulated ATP is used in organisms to drive endergonic reactions, because it is high in potential! Hydrolysis of bond between two outermostphosphate groups − -> formation of ADP and Pi (H P2 ) 4n a highly exergonic reaction -> 7.3 kcal of energy released mole of ATP -> in cells this energy is not lost as heat! Instead: Transfer of released phosphate group to a protein -> Phosphorylation -> usually causes change in protein's shape Phosphorylation changes shape and activity of proteins How does ATP drive endergonic reactions? Coupling between phosphorylationand endergonic reactions! • Protein phosphorylation- exergonic phosphorylation reaction paired with endergonic reaction -> energetic coupling • In cells, endergonic reactions becomeexergonic when substrate or enzymes involved are phosphorylated -> exergonic phosphorylation reaction • Phosphorylation(adding negative charge) drives endergonic reactions • Adding a negatively charged phosphate group to a protein changes the protein’s structure -> Activation of enzymes or reactants Energetic coupling provides the energy to phosphorylate enzymes and reactants when ATP loses a Pi How is ATP generated through cellular respiration? Where does the energy come from, to generate ATP from ADP and Pi? -> Breakdown of glucose in series of redox reactions What Is a Redox Reaction? • Reduction–oxidationreactions (redox reactions) in cellular respiration ○ Chemical reactions involving loss or gain of an electron ○ Release of energy stored in organic molecules ○ Released energy is ultimatelyused to synthesize ATP • Oxidation - loss of electrons • Reduction – gain of electrons • Oxidation events are always coupled with a reduction ○ An electron donor always paired with an electron acceptor. • During a redox reaction, electrons can be transferred completelyfrom one atom to another, or they can shift their position in covalent bonds. Photosynthesis – an example for redox reactions and the gain & loss of electrons An Overview of Cellular Respiration • Glucose (animals) or sucrose (plants) are key intermediaryin cell metabolism • Cells use glucose to buil
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