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METABOLISM
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Cell Metabolism Sum of all chemical reactions Catabolic pathways:
break down release energy cellular respiration Anabolic pathways: build consume energy photosynthesis
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ENERGY Capacity to do work Kinetic: energy of motion Potential: stored
Chemical: potential, stored in molecules Thermodynamics Energy cannot be created or destroyed Energy transformation ↑ entropy of universe
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Free energy – portion that can perform work when temp
Free energy – portion that can perform work when temp. uniform; available for work
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Exergonic and Endergonic Reactions
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Closed & Open Systems Glucose is broken down in a series of exergonic reactions that power the work of the cell. The product of each reaction becomes the reactant for the next
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ATP – adenosine triphosphate
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Energy coupling by phosphate transfer.
ATP hydrolysis provides the energy to convert glutamic acid to glutamine
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ATP CYCLE ATP + H20↔ ADP + Pi + energy
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ENZYMES Organic catalysts Lower activation energy Substrate specific
Active site Affected by environmental factors Not consumed in the reaction
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Hydrolysis of Sucrose
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REACTANTS AB: sucrose (glucose & fructose) CD: water (hydroxyl & hydrogen) PRODUCTS AC: glucose BD: fructose
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Enzymes lower activation energy
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Inhibition of Enzyme Activity
No inhibition – substrate can bind to active site Competitive inhibition – inhibitor mimics the substrate and competes for the active site. Noncompetitive inhibition – inhibitor binds to enzyme at site other than active site and alters the shape of the active site (no longer functional)
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Allosteric Interactions
Two or more polypeptides subunits, both with active sites. Allosteric sites – specific receptors for enzyme regulators, may be activators or inhibitors. Changes in response to concentration of regulators AMP (activator) & ATP (inhibitor) may fit same allosteric site
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Feedback Inhibition Ex. Inhibition of ATP generating pathway
Switching off of a pathway by its end product Promotes cell efficiency – cell does not waste resources making more product than necessary
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Cooperativity - amplifies the response to substrates -one substrate primes an enzyme to readily accept additional molecules
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Localization: Cell structures bring order
Multienzyme complex: assembles team of enzymes for entire metabolic pathway Fixed location within cell on membranes In solution within organelles
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