Molecular Biology – 6 hours

1 At least 2 questions from this section will be on the final exam SAMPLE QUESTIONS FOR THE FINAL EXAM Question 1. Ferritin is a protein involved in the storage of iron inside cells. To prevent toxic accumulation of too much iron inside cells, the intracellular level of ferritin is tightly regulated. To study the regulation of ferritin synthesis, mammalian cells are grown with or without iron in the culture medium. Note that iron in the culture medium is rapidly transported inside cells. a) Upon addition of iron to the culture medium, the intracellular concentration of ferritin mRNA is unchanged but the concentration of ferritin protein increases. How do you think ferritin expression is regulated? Briefly explain. The regulatory sequence given below is found in the ferritin mRNA between the cap structure and the start codon. 5’-GGGUUUCCGUUCAACAGUGCUUGGACGGAAACCC-3’ Mutations within in this sequence are used to study the regulation of ferritin expression. The following observation are made: • ferritin expression is high, independent of the iron concentration, when (i) the entire region is deleted, or (ii) the region located upstream of the underlined sequence is deleted or (iii) the underlined sequence is replaced with a random sequence. • ferritin expression remains iron-dependent when this region is replaced by the following sequence: 5’-GGGCUCAGGUUCAACAGUGCUUGGACCUGAGCCC-3’. Note that the sequence differences are indicated in bold. b) Explain why these observations suggest that both sequence and structure of the 5’ end of ferritin mRNA are important for the regulation of ferritin expression. c) Ferritin translation becomes iron-independent when the regulatory sequence is moved from the 5’ side (upstream of the open reading frame) to the 3’ side (downstream of the open reading frame) of ferritin mRNA. Which step of ferritin translation do you think is affected by the intracellular level of iron? d) IRP is a protein involved in the regulation of ferritin expression….