Biochem-Enzymes

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PicOlio
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117954
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Biochem-Enzymes
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2011-11-27 14:07:01
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Biochem enzymes
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Intro to Biochem Enzymes
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  1. Enzyme
    A biological catalyst that increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy.

    Enzymes are large molecules that increase the rates of chemical reactions without themselves undergoing any change.

    In short, enzymes lower the activation energy required to speed up the reaction.
  2. The vast majority of all known enzymes are _______ proteins.
    The vast majority of all known enzymes are globular protein-based enzymes.
  3. Ribozymes
    Ribozymes are enzymes made of ribonucleic acids. They catalyze the self-cleavage of certain proteins of their own molecules and have been implicated in the reaction that generates peptide bonds.

    Many biochemists believe that during evolution RNA catalysts emerged first, with protein enzymes arriving on the scene later.
  4. Substrate specificity
    The limitation of an enzyme to catalyze specific reactions with specific substrates.

    The specificity of enzymes also extends to stereospecificity. (An enzyme may catalyze a reaction on an L-isomer but not the D-isomer)
  5. The names of most enzymes ends in -___
    The names of most enzymes ends in -ase.
  6. Some enzymes have older (non -ase ending) names. Among these are ____, _____, and ____, all enzymes of the digestive tract.
    Pepsin, Trypsin, and Chymotrypsin
  7. Name the six major classification groups of enzymes.
    • 1. Oxidoreductases (catalyze oxidations and reductions)
    • 2. Transferases (catalyze the transfer of a group of atoms, such as from one molecule to another)
    • 3. Hydrolases (catalyze hydrolysis reactions)
    • 4. Lyases (catalyze the addition of two groups to a double bond or the removal of two groups from adjacent atoms to create a double bond.
    • 5. Isomerases (catalyze isomerization reactions)
    • 6. Ligases or Synthetases (catalyze the joining of two molecules.
  8. Cofactor
    The nonprotein part of an enzyme necessary for its catalytic function.
  9. Coenzyme
    A nonprotein organic molecule, frequently a B vitamin, that acts as a cofactor.
  10. Active Site
    A three-dimensional cavity of the enzyme with specific chemical properties that enable it to accommodate the substrate.
  11. Inhibitor
    A compound that binds to an enzyme and lowers its activity.
  12. Apoenzyme
    The protein (polypeptide) portion of the enzyme is called an apoenzyme.
  13. Substrate
    The compound on which the enzyme works, and whose reaction it speeds up, is called the substrate.
  14. Competitive Inhibitors
    Competitive inhibitors bind to the active site of the enzyme surface, thereby preventing the binding of substrate.
  15. Noncompetitive Inhibitors
    Noncompetitive inhibitors bind to some other portion of the enzyme surface (other than the active site) and sufficiently alter the tertiary structure of the enzyme so that its catalytic effectiveness is eliminated.
  16. Enzyme Activity
    Enzyme activity is a measure of how much reaction rates are increased.
  17. Lock-and-Key Model
    A model explaining the specificity of enzyme action by comparing the active site to a lock and the substrate to a key.
  18. Induced-fit Model
    A model explaining the specificity of enzyme action by comparing the active site to a glove and the substrate to a hand.
  19. What are the five most common amino acids found in the active sites of enzymes?
    • Histidine (His)
    • Cysteine (Cys)
    • Asparagine (Asp)
    • Arginine (Arg)
    • Glutamine (Glu)
  20. Nucleophilic Attack
    A chemical reaction where an electron-rich atom, such as oxygen or sulfur, bonds to an electron-deficient atom, such as carbonyl carbon.
  21. Feedback Control
    Feedback control is an enzyme regulation process in which formation of a product inhibits an earlier reaction in the sequence.

  22. Proenzyme (zymogen)
    A protein that becomes an active enzyme only after undergoing a chemical change.

    This is important in things like digestion where some enzymes are used to cleave proteins but should not do so to all proteins in the body!
  23. Allosteric enzyme
    An enzyme in which the binding of a regulator on one site on the enzyme modifies the enzyme's ability to bind the substrate in the active site.

    • Negative modulation inhibit enzyme action
    • Positive modulation stimulate enzyme action

    • R form more active relaxed form
    • T form less active taut form
  24. Isozymes (Isoenzymes)
    Enzymes that perform the same function but have different combinations of subunits and thus different quaternary structures.

    "Different forms of the same enzyme"
  25. What is the difference between a catalyst and an enzyme?
    A catalyst is any substance that speeds up the rate of a reaction and is not itself changed by the reaction.

    An enzyme is a biological catalyst, which is either a protein or an RNA molecule.
  26. Why does the body need so many different enzymes?
    Because enzymes are very specific and thousands of reactions must be catalyzed in an organism.
  27. Both lyases and hydrolases catalyze reactions involving water molecules. What is the difference in the types of reactions that these two enzymes catalyze?
    Lyases add water across a double bond or removes water from a molecule, thereby generating a double bond.

    Hydrolases use water to break an ester or amide bond, thereby generating two molecules.
  28. What is the difference between a coenzyme and a cofactor?
    Cofactor is more generic; it means a nonprotein part of an enzyme.

    A coenzyme is an organic cofactor.
  29. What is the difference between reversible and irreversible noncompetitive inhibition?
    In reversible inhibition, the inhibitor can bind and then be released.

    With noncompetitive inhibition, once the inhibitor is bound, no catalysis can occur. With irreversible inhibition, once the inhibitor is bound, the enzyme would be effectively dead, as the inhibitor could not be removed and no catalysis could occur.
  30. Which amino acids appear most frequently in the active sites of enzymes?
    The amino acid residues most often found at enzyme active sites are His, Cys, Asp, Arg, and Glu.
  31. What is the difference between a zymogen and a proenzyme?
    There is no difference. They are the same.

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