Chapter 8 Possible Essay Questions

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  1. 1)      How do enzymes use energy? 
    a.       In cellular respiration, the free energy contained in small molecules derived from food is converted first into the free energy of an ion gradient and then into a different currency—the free energy of ATP. Enzymes transform energy. They can convert light to sugar, sugar to ATP, and ATP to electrical gradients and mechanical movement. 
  2. 1)      What is the evidence of the ES complex? 
    a.       First, the fact that the rate of the reaction demonstrates no change after it gets saturated means that all of the active sites must be filled. Furthermore, X-ray crystallography shows that the substrate binds to the enzyme. Also, putting in enzymes and substrates demonstrates similar curves with different conversations. 
  3. 1)      Explain the structure of a general active site. 
    a.       It is a 3D cleft that is formed from residues of the amino acid sequence that come together and are held together by hydrogen bonds. Residues that are farther apart interact with one another. The active site takes up only a small portion of the active site. Even though the enzyme is large and globular, the rest of the amino acids serve as the scaffold. The catalytic groups, which are the enzymes in the active site, are the only ones that contribute to enzyme function. Active sites are unique microenvironments that can include or exclude only what is needed. Substrates are also bound to enzymes by multiple weak interactions. Covalent bonds can form, but they cause more permanent bonds. Finally, the specificity of binding depends on the precisely defined arrangement of atoms in an active site. The maximum binding energy can only come from perfect interaction with the substrate and enzyme. The way they fit together is the induced fit. 
  4. 1)      Why does penicillin function so well? 
    a.       Penicillin functions so well because it acts as a suicide inhibitor to glycopeptide transpeptidase. The function of penicillin is a thiazolidine ring with a beta-lactam ring and a variable R group. This will inhibit the cross –linking of glycopeptide transpeptidase, which forms the crosslinks between amino acid residues in bacteria. In bacteria, there are peptidoglycan walls, with NAM and NAG that are linked by tetrapeptides and peptaglycines. Glycopeptide does this by reacting with the penultimate D-Ala of the substrate, forming the acyl intermediate, which then goes on to react with an glycine in another peptide to form the cross-link. Because penicillin has the D-Ala-D-Ala moiety of the usual substrate, it will begin to form the acyl intermediate that glycopeptide transpeptidase normally forms. However, instead of binding the alanine, a serine in the active site attacks the carbonyl carbon of the beta-lactam ring, forming a covalent bond that prevents the enzyme from reacting any further. 
  5. How can Km and Vmax be determined? 
    • - one way is to measure them at a variety of substrate concentrations if an enzyme operates according to the simple scheme given by V0=Vmax ([S]/[S] + Km)
    • - another way is using the Lineweaker Burks plot
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Chapter 8 Possible Essay Questions
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