chapter 21 enzymes and vitamins n.
Skip this Video
Loading SlideShow in 5 Seconds..
Chapter 21 Enzymes and Vitamins PowerPoint Presentation
Download Presentation
Chapter 21 Enzymes and Vitamins

Chapter 21 Enzymes and Vitamins

413 Vues Download Presentation
Télécharger la présentation

Chapter 21 Enzymes and Vitamins

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Chapter 21 Enzymes and Vitamins 21.5 Enzyme Inhibition 21.6 Regulation of Enzyme Activity 21.7 Enzyme Cofactors

  2. Enzyme Inhibition Inhibitors: • Are molecules that cause a loss of catalytic activity. • Prevent substrates from fitting into the active sites. E + S ES E + P E + I EI no P

  3. Reversible Competitive Inhibition A competitive inhibitor: • Has a structure like the substrate. • Competes with the substrate for the active site. • Has its effect reversed by increasing substrate concentration.

  4. Noncompetitive Inhibition A noncompetitive inhibitor: • Has a structure different than the substrate. • Distorts the shape of the enzyme, which alters the shape of the active site. • Prevents the binding of the substrate. • Cannot have its effect reversed by adding more substrate.

  5. Malonate and Succinate Dehydrogenase Malonate: • Is a competitive inhibitor of succinate dehydrogenase. • Has a structure that is similar to succinate. • Inhibition is reversed by adding succinate.

  6. Irreversible Inhibition • Loss of all enzymatic activity • Toxic substance (irreversible inhibitor) forms a covalent bond with an amino acid in the active center. • Prevents the substrate from entering the active site. • Prevents the catalytic activity. • Examples: insecticides and nerve gases inhibit the enzyme acetylcholinesterase (needed for nerve conduction).

  7. Irreversible inhibitor DFP (diisopropyl fluorophosphate) • DFP forms a covalent bond with the OH group of the amino acid serine in the active site of the enzyme acetylcholinesterase. • Acetylcholinesterase is inhibited. • The transmission of nerve impulses is blocked. • Paralysis occurs.

  8. Irreversible Inhibition • In irreversible inhibition, a substance destroys enzyme activity by bonding with R groups at the active site.

  9. Zymogens Zymogens (proenzymes): • Are inactive forms of enzymes. • Are activated when one or more peptides are removed. • Such as proinsulin is converted to insulin by removing a small peptide chain.

  10. Digestive Enzymes Digestive enzymes are: • Produced as zymogens in one organ and transported to another such as the pancreas when needed. • Activated by removing small peptide sections.

  11. Allosteric Enzymes • An allosteric enzyme is an enzyme in a reaction sequence that binds a regulator substance. • A positive regulator enhances the binding of substrate and accelerates the rate of reaction. • A negative regulator prevents the binding of the substrate to the active site and slows down the rate of reaction.

  12. Feedback Control In feedback control: • A product acts as a negative regulator. • An end product binds with the first enzyme (E1) in a sequence, when sufficient product is present.

  13. Enzyme Cofactors • A simple enzyme is an active enzyme that consists only of protein. • Many enzymes are active only when they combine with cofactors such as metal ions or small molecules. • A coenzyme is a cofactor that is a small organic molecule such as a vitamin.

  14. Enzyme Cofactors

  15. Metal Ions as Cofactors • Many active enzymes require a metal ion. • Zn2+, a cofactor for carboxypeptidase, stabilizes the carbonyl oxygen during the hydrolysis of a peptide bond.

  16. Some Enzymes and Their Cofactors