Draw the reaction mechanisms that are catalyzed by the splic

Draw the reaction mechanisms that are catalyzed by the spliceosome. Cordycepin inhibits poly(A) synthesis at low concentrations and RNA synthesis at higher concentrations. a. What is the basis of inhibition by cordycepin? b. Why is poly(A) synthesis more sensitive to the presence of cordycepin? c. How does cordycepin need to be modified to exert its effect? Draw the structure for the peptide S-P-R-l-N-G at physiological pH. Identify the primary intermolecular force that each side chain would have with other species (water, another side chain, etc.) at this pH. Circle the peptide bonds.

Solution

Answer:

(a) cordycepin, which is an inhibitor of poly-A synthesis at the 3’ end of mRNA. At high concentrations it affects all RNA synthesis The molecule is rejected by DNA polymerase because of the 2’ OH group.Because cordycepin lacks a 3-OH group, it cannot participate in 3 5 bond formation.

(b) Cordycepin (3’-deoxyadenosine) after uptake into the cell, is phosphorylated to 3’-deoxyadenosine 5’-triphosphate (3’- dATP), which probably represents the active form of the inhibitor of poly(A) synthesis. Because the poly(A) tail is a long stretch of adenosine nucleotides, the likelihood that a molecule of cordycepin would become incorporated is higher than with most RNA.

(c) Cordycepin (3’-deoxyadenosine), after uptake into the cell, is phosphorylated to 3’-deoxyadenosine 5’-triphosphate (3’- dATP).