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Chapter 20 Enzymes and Vitamins

Chapter 20 Enzymes and Vitamins. 20.2 Enzyme Action. Active Site. The active site is a region within an enzyme that fits the shape of the reacting molecule, called a substrate contains amino acid R groups that bind the substrate releases products when the reaction is complete.

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Chapter 20 Enzymes and Vitamins

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  1. Chapter 20 Enzymes and Vitamins 20.2Enzyme Action

  2. Active Site The active site • is a region within an enzyme that fits the shape of the reacting molecule, called a substrate • contains amino acid R groups that bind the substrate • releases products when the reaction is complete

  3. Enzyme-Catalyzed Reaction • The proper fit of a substrate (S) in an active site on an enzyme (E) forms an enzyme–substrate (ES) complex. E + S ES • Within the ES complex, the reaction occurs to convert substrate to product (P). ES E + P • The products, which are no longer attracted to the active site, are released. • Overall, substrate is converted to product. E + S ES E + P

  4. Enzyme-Catalyzed Reaction (continued) In an enzyme-catalyzed reaction, • a substrate attaches to the active site • an enzyme–substrate (ES) complex forms • reaction occurs and products are released • an enzyme (E) is used over and over E + S ES E + P

  5. Enzyme Specificity Enzymes may recognize and catalyze • a single substrate • a group of similar substrates • a particular type of bond

  6. Lock-and-Key Model In the lock-and-key model of enzyme action, • the active site has a rigid shape • only substrates with the matching shape can fit • the substrate is the key that fits that lock

  7. Induced-Fit Model In the induced-fit model of enzyme action, • enzyme structure is flexible, not rigid • shapes of enzyme and substrate adjust for best fit at the active site to improve catalysis of reaction • substrate specificity increases

  8. Example of an Enzyme-Catalyzed Reaction

  9. Learning Check A. The active site is 1) the entire enzyme 2) a section of the enzyme 3) the substrate B. In the induced-fit model, the shape of the enzyme when substrate binds 1) stays the same 2) adapts to the shape of the substrate

  10. Solution A. The active site is 2) a section of the enzyme B. In the induced-fit model, the shape of the enzyme when substrate binds 2) adapts to the shape of the substrate

  11. Isoenzymes Isoenzymes • catalyze the same reaction in different tissues in the body • such as lactate dehydrogenase (LDH), which converts lactate to pyruvate, consist of five isoenzymes • can be used to identify the organ or tissue involved in damage or disease • such as LDH have one form more prevalent in heart muscle and another form in skeletal muscle and liver tissue

  12. Isoenzymes (continued)

  13. Diagnostic Enzymes Diagnostic enzymes • determine the amount of damage in tissues • that are elevated may indicate damage or disease in a particular organ

  14. Diagnostic Enzymes (continued) Levels of the enzyme creatine kinase (CK), lactic dehydrogenase (LDH), and aspartate transaminase (AST) • are elevated following a heart attack • are used to determine the severity of the attack

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