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  1. Please Take out the Following • Pencil • Science Journal • Agendas • Macromolecules Worksheet (Pass it forward if you have not done so already). • Plan for the week

  2. Science Question of the Day • Explain why the chemical bonds in the body do not break down, spontaneously, releasing all of their energy.

  3. 5.3 Chemical Reactions • Chemical reactions begin with reactants(substrates) which are converted to products • Exergonic reactions • Products contain less energy than the reactants • Endergonic reactions • Products contain more energy than the reactants

  4. Fig. 5.4 • Energy of Activation • Extra energy required to destabilize chemical bonds and so initiate a chemical reaction

  5. Fig. 5.4 • Catalysts lower the activation energy of a reaction, and thus increase its rate • However, they cannot make an endergonic reaction exergonic

  6. 5.4 How Enzymes Work • Enzymes are proteins that serve as catalysts • They speed up chemical reactions within cells • Enzymes bind a specific molecule and stress bonds to make a particular reaction more likely • Active site • Site on enzyme surface where reactant fits • Binding site • Site on reactant where enzyme binds

  7. Fig. 5.5 Enzyme shapes determines its activity Lysozyme Changes upon binding of the substrate The substrate is now bound more intimately

  8. Fig. 5.6 How enzymes work

  9. Fig. 5.7 The catalytic cycle of an enzyme 1 2 3 4 The substrate, sucrose, consists of glucose and fructose bonded together. Glucose Fructose The substrate binds to the enzyme, forming an enzyme-substrate complex. Bond Products are released, and the enzyme is free to bind other substrates. H2O The binding of the substrate and enzyme places stress on the glucose-fructose bond, and the bond breaks. Active site Enzyme

  10. 5.5 Factors Affecting Enzyme Activity • Enzyme activity is affected by any change in condition that alters the enzyme’s 3-D shape • The structural bonds of enzymes are sensitive to changes in temperature and pH • Therefore, a temperature or pH beyond the optimal range will cause the enzyme to denature

  11. Enzyme Activity

  12. Fig. 5.8 Enzymes are sensitive to their environment Digests proteins in the stomach Digests proteins in the intestine

  13. 5.6 How Cells Regulate Enzymes • A cell can control the activity of an enzyme by altering its shape • Allosteric enzymes have shapes that can be altered by the binding of signal molecules • These molecules bind to the allosteric site • Repressors bind and repress enzyme activity • Activators bind and restore or increase enzyme activity

  14. Fig. 5.9 How cells control enzymes

  15. Fig. 5.10 Competitive inhibition - Inhibitor binds at the enzyme’s active site Noncompetitive inhibition - Inhibitor binds at the enzyme’s allosteric site • Enzyme inhibition occurs in two ways:

  16. Enzymes Reviewed