1. Which of the following statements regarding the action of the enzyme, RNAase

Question

1. Which of the following statements regarding the action of the enzyme, RNAase A, is most FALSE?

a) His119 acts as an Bronsted acid and base during the course of a reaction.

b) The phosphorus atom in the bridging phosphodiester bond of the RNA substrate acts as an electrophile.

c) In a resting enzyme, not bound to substrate, His12 is in its deprotonated form.

d) His-12 removes a proton from the alcohol at the 2' position of the ribose, which makes the alcohol into a good leaving group.

2. Which of the following statements is most FALSE regarding the activity of His12 in RNase A?

a) His12 does not bind directly to the substrate to form an enzyme-substrate covalent intermediate

b) The protonation state of His12 is restored by donating a proton to the RNA leaving group

c) His12 initially acts as a general base, removing a proton from the 2'-OH group of the ribose sugar

d) His12 removes a proton from water, generating a nucleophilic hydroxide group

3. Sequence-specific, DNA-binding proteins, such as transcription factors, are most likely to interact with which part of B-form DNA?

a) the 5' end

b) The 3' end

c) the major groove

d) the minor groove

e) the phosphate backbone

4. Which statement is most false regarding nucleic acids?

a) RNA is generally less stable than DNA due to the presence of presence of RNase enzymes in the environment

b) Deoxyribose and ribose have -OH groups at their 3' position.

c) The 5' end of a DNA polymer possesses an unreacted -OH group on it's 3' carbon

d) A double-stranded DNA polymer composed of guanine and cytosines would possess more hydrogen bonds than a molecule composed of adenine and thymines.

Explanation / Answer

1.d) His-12 removes a proton from the alcohol at the 2' position of the ribose, which makes the alcohol into a good leaving group.

2.d) His12 removes a proton from water, generating a nucleophilic hydroxide group

3. c) the major groove

4. c) The 5' end of a DNA polymer possesses an unreacted -OH group on it's 3' carbon

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