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Protein Structure and Enzymatic Reactions: Role of Active Sites and Allosteric Regulation

This course explores the structure of proteins, focusing on the role of active sites in enzymatic reactions. It explains how enzyme-substrate complexes form, the impact of active sites on reaction progress, and the effects of inhibitors and activators on enzyme function. Additionally, the course covers the quaternary structure of proteins and important proteins involved in cellular processes.

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Protein Structure and Enzymatic Reactions: Role of Active Sites and Allosteric Regulation

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  1. AP Biology Living Metabolism Part 2

  2. Proteins

  3. 2’ structure

  4. Course of reaction without enzyme EA without enzyme EA with enzyme is lower . Reactants Free energy Course of reaction with enzyme DG is unaffected by enzyme Products Progress of the reaction

  5. Substrate . Active site Enzyme-substrate complex Enzyme

  6. Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. • Active site (and R groups of • its amino acids) can lower EA • and speed up a reaction by • acting as a template for • substrate orientation, • stressing the substrates • and stabilizing the • transition state, • providing a favorable • microenvironment, • participating directly in the • catalytic reaction. Substrates . Enzyme-substrate complex Active site is available for two new substrate molecules. Enzyme Products are released. Substrates are converted into products. Products

  7. R groups of Amino Acids

  8. Optimal Performance

  9. 2’ structure

  10. 3’ Structure

  11. Denaturation of a protein

  12. A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme Normal binding . A competitive inhibitor mimics the substrate, competing for the active site. Competitive inhibitor Competitive inhibition A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. Noncompetitive inhibitor Noncompetitive inhibition

  13. Reaction rates for each condition

  14. Allosteric activator stabilizes active form. Allosteric enzyme with four subunits Active site (one of four) . Regulatory site (one of four) Activator Active form Stabilized active form Oscillation Allosteric inhibitor stabilizes inactive form. Non- functional active site Inhibitor Stabilized inactive form Inactive form Allosteric activators and inhibitors

  15. Initial substrate (threonine) Active site available Threonine in active site Enzyme 1 (threonine deaminase) Isoleucine used up by cell Feedback Inhibition or Negative Feedback Intermediate A Feedback inhibition Enzyme 2 Active site of enzyme 1 can’t bind theonine pathway off Intermediate B Enzyme 3 Intermediate C Isoleucine binds to allosteric site Enzyme 4 Intermediate D Enzyme 5 End product (isoleucine)

  16. Binding of one substrate molecule to active site of one subunit locks all subunits in active conformation. Substrate . Inactive form Stabilized active form Cooperativity another type of allosteric activation

  17. Polypeptide chain b Chains Proteins involved in constructing a red blood cellQuaternaryStructure Iron Heme a Chains Hemoglobin Polypeptide chain Collagen

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