Question

A. Choose anly one correcet answer for each of the following questions (4 pts cach). AL Some and KM values are shown below for enzyme-substrate pairs. Which of the following enzymes is most efficient in converting the substrate into the product? b) kes.-4x10s s", KM-0.026 M d)k,,-5.7 x1o's", K-2x10s M c)人at-900 s", KM-2.5 × 10.5 M A2. Which of the following enzyme reaction mechanisms has multiple substrates? a) induced-fit e) Michaclis-Menton b) random sequential d) reversible covalent modification e) None of the above A3. In this type of inhibition, the inhibitor can bind to the enzyme regardless of whether the substrate has already bound to the enzyme or not. e) None of the above d) All of the above a) competitive b) noncompetitive c) uncompetitive A4. Which of the following statements concerning enzyme inhibition is correct? a) In uncompetitive inhibition, the substrate and the inhibitor bind to the same site. b) In competitive inhibition, Km increases. c) In noncompetitive inhibition, Vmas increases. d) Uncompetitive inhibition is an example of irreversible enzyme inhibition e) An irreversible inhibitor binds to the enzyme by hydrogen bonding. A5. Which of the following is NOT a common catalytic strategy used by many enzymes? a) catalysis by reduction b)metal ion catalysis e) general acid-base catalysis c) catalysis by approximation d) covalent catalysis A6. The specificity of chymotrypsin is accounted for by a) covalent binding of a His residue to the substrate b) binding of the N-terminus amino acid at the active site c) interaction of the active site amino acids with the substrate d) binding of the proper amino acid into a deep pocket on the enzyme e) conformational change upon binding of substrate A7. A region of the active site that stabilizes the tetrahedral reaction intermediate is a) catalytic triad b) oxyanion hole c)Sipocket d) active site e) regulatory site

Answer 1

Keat- K M 02 6 ax 3 2 Cr 2-S 지。

2. Multiple substrate enzyme reaction mechanism is random sequential.

3. Non-conmpetitive inhibition is a type of enzyme inhibition where the inhibitor reduces the activity of the enzyme and binds equally well to the enzyme whether or not it has already bound the substrate.

4. When a non-competitive inhibitor is added the Vmax is changed, while the Km remains unchanged. V_max is reduced during the addition of a non-competitive inhibitor. The uncompetitive inhibitor adds on to enzyme-substrate complex and substrate binds to enzyme only, and the reaction is reversible.In competitive inhibition, the maximum velocity V_max of the reaction is unchanged and When a competitive inhibitor is bound to an enzyme the K_m increases. Irreversible inhibition corresponds to strong covalent bonding, reversible inhibitors form hydrogen bonds.

So the correct option is (b).

5. In covalent catalysis, the active site contains a reactive group, usually a powerful nucleophile that becomes temporarily covalently modified in the course of catalysis. In general acid-base catalysis, a molecule other than water plays the role of a proton donor or acceptor. Metal ions can function catalytically in several ways. For instance, a metal ion may serve as an electrophilic catalyst, stabilizing a negative charge on a reaction intermediate. Alternatively, the metal ion may generate a nucleophile by increasing the acidity of a nearby molecule. In catalysis by approximation, the reaction rate may be considerably enhanced by bringing the two substrates together along a single binding surface on an enzyme.

So the uncommon catalytic strategy is (a) catalysis by reduction.

6. Chymotrypsin's inherent specificity allows it to act only on the carboxy-terminal of aromatic residues, showing specificity for aromatic amino acids because of its hydrophobic pocket. So answer is (d).