Please See Attachment Document Preview 1: At Least 2 Questio

Please See Attachementdocument Preview1 At Least 2 Questions From Thi

Please see attachment Document Preview: 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....

Paper For Above instruction

The regulation of ferritin expression in mammalian cells exemplifies a sophisticated mechanism that ensures iron homeostasis and prevents toxicity. Central to this regulation is the role of Iron Regulatory Proteins (IRPs), which interact with specific sequences in ferritin mRNA, primarily within its untranslated regions, to modulate translation depending on intracellular iron levels.

Ferritin, a crucial iron-storage protein, maintains cellular iron balance by sequestering excess iron. Interestingly, studies reveal that when mammalian cells are exposed to increased iron levels, ferritin protein levels rise without a corresponding increase in ferritin mRNA. This indicates post-transcriptional regulation, whereby the mRNA remains stable but translation efficiency is modulated.

One of the key elements in this regulation involves sequences located in the 5' untranslated region (UTR) of ferritin mRNA. Experimental data demonstrate that deletion of the entire regulatory region or mutations upstream of the core sequence lead to high, iron-independent ferritin expression. Conversely, maintaining the native sequence or substituting it with a sequence with minimal structural change preserves iron-dependent regulation.

These observations suggest that both the nucleotide sequence and secondary structure of the 5’ UTR are critical for the regulation of ferritin translation. Specifically, the presence of IRP binding sites within this region allows the protein to sense iron levels and accordingly inhibit or permit translation. When iron levels are low, IRPs bind to these sites, blocking translation initiation. When iron is abundant, IRPs dissociate, allowing translation to proceed. Mutations disrupting this interaction lead to loss of iron sensitivity, resulting in constitutive ferritin expression regardless of iron status.

Furthermore, the relocation of the regulatory sequence from the 5’ to the 3’ UTR alters the regulation, making ferritin translation independent of iron levels. This shift indicates that the mechanism by which IRPs modulate translation relies on their ability to bind to sequences accessible in the 5’ UTR, thereby affecting translation initiation rather than other steps like elongation or termination.

IRPs, therefore, serve as molecular sensors for cellular iron levels, binding to Iron-Responsive Elements (IREs) in the 5’ UTR of ferritin mRNA under low iron conditions, and dissociating when iron is plentiful. This dynamic interaction exemplifies a finely tuned post-transcriptional regulation system that balances iron storage with cellular needs, protecting cells from iron-mediated oxidative damage while ensuring sufficient iron availability.

References

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