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Thought Question 2 Due Fri. 9/15/00 (in class)The information needed for this question comes from
your lecture notes, the question, the text and your own head. Please
follow length limitations given. Preference
is for the assignment to be typed. For many years, enzymatic activity was thought to be
exclusively attributable to proteins.
However, it was discovered that some RNAs, called ribozymes, can
also direct enzymatic reactions, without the intervention of proteins.
In recent years, many examples of ribozymes have been identified,
and it is now commonly accepted that while most enzymes are proteins,
there are a significant number of ribozymes in the biological world. I.
[6 pts] Think about the sorts of secondary structures and tertiary
interactions that allow proteins to fold into specific three dimensional
structures and enable them to function as enzymes. Using similar
structural considerations and proper terminology for nucleic acid
structure, explain why RNA makes a good catalytic molecule and conversely
why DNA does not (Refer to Karp Fig. 2.48 and Fig. 11.43 for examples of
RNA structure, and 10.10ac for DNA).
Limit your answer to 3 sentences. II.
[4 pts] The majority
of ribozymes act on nucleic acids, often cleaving phosphodiester linkages
at specific sequences in RNA or possibly even DNA (i.e.
ribonucleases or deoxyribonucleases).
Why is it not surprising, again in structural terms, that an enzyme
composed of RNA would evolve to recognize and cleave itself or other RNA
or DNA? (Hint:: Enzymes bind to
their substrates by recognizing unique chemical or structural features of
that substrate). Limit
your answer to 2 sentences. |