Chem Ch. 20

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Chem Ch. 20
2010-03-30 19:18:07
Enzymes and Vitamins

Enzymes and Vitamins
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  1. Why are enzymes needed in biological reactions?
    Uncatalyzied reactions want take place fast enough for survival
  2. Why does an enzyme catalyze a reaction of only certain substrates?
    This combination of an enzyme and a substrate provides an alternative pathway for the reaction witha lower activation energy
  3. Why does the enzyme catalyzed hydrolysis of sucrose go faster than the hydrolysis of sucrose in the chemistry lab?
    When a molecule of sucrose binds to the active site of sucrase, its glycosidic bond is in a position favorable for reaction
  4. How does the induced-fit model differ from the lock-and-key model?
    In the lock-and-key model, a substrate fits the shape of the active site and forms and enzyme-substate complex. In the induced-fit model, a flexible active site and substrate adjust shape to provide the best fit for the reaction.
  5. Why is 37oC the optimum temperature for many enzymes?
    This is body temp
  6. Why does the digestive enzyme pepsin have an optimum pH of 2?
    Its most active when stomach acid is most active; i.e. after eating/ during digestion
  7. What happens to the rate of reaction when substrate saturates that enzyme?
    Increasing the substrate concentration increases the rate of reaction until the enzyme molecules are saturated with substrate
  8. Does an increase in substrate concentration reverse the inhibition by a competitive inhibitor?
    Yes, adding more substrate displaces the competitive inhibitor, which increases the rate of the reaction.
  9. Does an increase in the substrate concentration reverse the inhibition by a noncompetitive inhibitor?
    Because a noncompetitive inhibitor isn't competing for the active site, the addtion of more substrate doesn't reverse this type of inhibition.
  10. Do the intermediate enzymes in a reaction sequence have regulatory sites?
  11. When would the Zn2+ be utilized as a cofactor by other enzymes?
    With the substrate in the active site, the Zn2+ helps to stablize the negative charge on the oxygen atom of the carbonyl group and promotes the hydrolysis of the peptide bond
  12. What is the function of water-soluble vitamins in enzymes?
    they are required by many enzymes as cofactors to carry out certain aspects of catalytic action
  13. What happens to any excess vitamin C that is consumed over the course of a day?
    its eliminated in the urine each day
  14. Why is vitamin A called a fat-soluble vitamin?
    it can be stored in the body
  15. Define: Active site
    A pocket in a part of the teritary enzyme structure that binds substrate and catalyzes a reaction
  16. What is the rate at which an enzyme catalyzes the reaction that converts substrate to product called?
  17. Define: Allosteric enzyme
    an enzyme that regulates the rate of a reaction when a regulator molecule attaches to a site other than the active site
  18. What are substances that are usually produced by bacteria, mold, or yeast that inhibit the growth of bacteria?
  19. Define: Coenzyme
    An organic molecule, usually a vitamin, required as a cofactor in enzyme action
  20. What is a metal ino or an organic molecule that is necessary for a biologically fuctional enzyme?
  21. Define: Competitive inhibitor
    a molecule with a structure similiar to the substrate that inhibits enzyme action by competing for the active site
  22. Define: Enzymes
    Globular proteins, sometimes with cofactors, that catalyze biological reactions
  23. What is an intermediate consisting of an enzyme that binds to a substrate in an enzyme-catalyzed reaction?
    Enzyme-substrate (ES) complex
  24. Define: Fat-soluble vitamins
    vitamins that are not soluble in water and can be stored in the liver and body
  25. What is a type of inhibition in which an end product inhibits the first enzyme in a sequence of enzyme-catalyzed reaction?
    Feedback control
  26. Define: Induced-Fit Model
    A model of enzyme action in which the shape of a substrate and the active site of the enzyme adjust to give an optimal fit
  27. What are substances that make an enzyme inactive by interfering with its ability to react with a substrate?
  28. Define: Irreversible inhibition
    The loss of enzymatic activity that can't be reversed
  29. What is a model of enzyme action in which the substrate is like a key that fits the specific shape of the active site (the lock)?
    Lock-and-key model
  30. Define: Noncompetitive inhibitor
    A type of inhibitor that alters the shape of an enzyme as well as the active site so that the substrate can't bind properly
  31. What is the pH at which an enzyme is most active called?
    Optimum pH
  32. Define: Optimum Temperature
    the temp at which an enzyme is most active
  33. What is the loss of enzymatic activity by an inhibitor whose effect can be reversed called?
    Reversible inhibition
  34. Define: Simple Enzyme
    An enzyme that is active as a polypeptide only
  35. What is the molecule that reacts in the active site in an enzyme-catalyzed reaction called?
  36. Define: Vitamins
    Organic molecules that are essential for normal health and growth and are obtained in small amounts from the diet
  37. What are vitamins thar are soluble in water; they can't be stored in the body, are easily destroyed by heat, ultraviolet light, and oxyge, and function as conenzymes?
    Water-soluble vitamins
  38. Define: Zymogen
    An inactive form of an enzyme that is activated by the removal of a peptide portion from one end of the protein.