1.  Like Jordan and Pippen. Match each term with its description. ✓ 4

2.  Nice hat. Describe the 5′ cap.

3.  Tales of the end. What are the steps required for the formation of a poly(A) tail on an mRNA molecule?

4.  Maturing. What are the three most common modifications by which primary transcripts are converted into mature mRNA?

5.  A coupling device. What structural component of RNA polymerase II that is lacking in RNA polymerases I and III allows modification of the newly synthesized RNA?

6.  Polymerase inhibition. 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) Does cordycepin need to be modified to exert its effect?

7.  Teamwork. What is a spliceosome, and of what is it composed?

8.  Recruiting the right team. What is the role of the carboxyl-terminal domain of RNA polymerase II in coupling RNA synthesis and splicing?

9.  From a few, many. Explain why alternative splicing effectively enlarges the size of the genome.

10.  Alternative splicing. A gene contains eight sites where alternative splicing is possible. With the assumption that the splicing pattern at each site is independent of those at all other sites, how many splicing products are possible? ✓ 4

11.  A good idea at the time. George Beadle and Edward Tatum were awarded the Nobel Prize for their research on the relation of genes to enzymes. In a paper published in 1941, they proposed the “one gene, one enzyme hypothesis,” which postulated that each gene encodes a single enzyme or, more generally, a single protein. Although this hypothesis was very influential, we now know that it is an oversimplification. Explain why.

12.  Searching for similarities. Compare self-splicing with spliceosome-catalyzed splicing.

13.  Proteome complexity. What process considered in this chapter makes the proteome more complex than the genome? What processes might further enhance this complexity? ✓ 4

14.  Separation technique. Suggest a means by which you could separate mRNA from the other types of RNA in a eukaryotic cell.

15.  A cell-cycle matter. Histone genes differ from most genes in eukaryotes in several ways. The genes are arranged in repeated arrays, with each array containing a gene for each of the five histones. Moreover, the histone genes do not contain introns. Finally, messenger RNAs encoded by histone genes do not have poly(A) tails attached after transcription. Propose an explanation for these remarkable characteristics in regard to histone function.

16.  An extra piece. In one type of mutation leading to a form of thalassemia, the mutation of a single base (G → A) generates a new 3′ splice site (blue in the adjoining illustration) like the normal one (yellow) but farther upstream.



What is the amino acid sequence of the extra segment of protein synthesized in a thalassemic patient having a mutation leading to aberrant splicing? The reading frame after the splice site begins with TCT.

17.  A long-tailed messenger. Another thalassemic patient had a mutation leading to the production of an mRNA for the β chain of hemoglobin that was 900 nucleotides longer than the normal one. The poly(A) tail of this mutant mRNA was located a few nucleotides after the only AAUAAA sequence in the additional sequence. Propose a mutation that would lead to the production of this altered mRNA.