Insulin Review Article Questions

1. In what journal did this article appear? When?
Science, Vol. 208; 4 April 1980

2. What is the primary purpose of this paper?
Publications of findings in the nucleotide structure of preproinsulin mRNA

3. What is the structural difference between insulin and proinsulin?
ProInsulin is a precursor to insulin. Insulin has the variable C chain, while proinsulin does not.

4. What is complementary DNA (cDNA)?
A sequence of DNA nucleotides that chemically match the other strand of the double stranded structure.

5. What is meant by the "polyA tail" or "polyadenylation" of a gene?
It is the polypeptide attached to the end of chain A.

6. What is meant by the statement that "insulin A and B chains are highly conserved"?
The chains are protected from evolution (unchanging).

7. Which chain is most highly conserved?
A chain

8. What do the researchers believe is the purpose of the C chain?
To help form the 3-D shape of the proinsulin molecule

9. Why does it make sense that the C chain is more variable (less highly conserved) than the A chain and B chain?
The C chain just binds them together and doesn’t have such specific functions as chains A and B; also, the variability will not make the chain function differently.

10. What do the researchers believe is the purpose of the pre-peptide (D chain)?
To signal the transfer of the preproinsulin protein into the ER.

11. How does the human preproinsulin gene differ from rat preproinsulin (rat I and rat II)?
Different codons in the coding area.

12. What is the first codon in the coding region of the gene (at the start of the pre-peptide) and what is the first amino acid in the polypeptide?
AUG; methionine (Met)