Let's analyze the data provided to determine which mutation is likely causing Lucy's ADA enzyme not to work effectively. Here are the facts based on the table:
- The gene length for both the normal range and Lucy is 1,500 base pairs, indicating there's no difference in the gene length.
- The mRNA length for both the normal range and Lucy is 1,500 nucleic acids, indicating the transcription process (from DNA to mRNA) is likely normal.
- The crucial difference is in the amino acid sequence: the normal range shows 500 amino acids, while Lucy's sequence shows only 283 amino acids, which is significantly shorter and categorized as low.
### Hypotheses for the Mutation
1. Active Site Mutation:
- An active site mutation typically affects the function of the enzyme without changing its length significantly. It alters the specific part of the enzyme where the substrate binds, resulting in a nonfunctional enzyme.
- However, Lucy's amino acid sequence is significantly shorter (283 vs. 500), suggesting that the entire protein length is affected, not just a change in its activity site.
2. Stop Codon Mutation:
- A stop codon mutation can introduce a premature stop codon in the mRNA sequence. This would result in the truncated translation of mRNA, producing a shorter and likely nonfunctional protein.
- Given that Lucy's protein is 283 amino acids instead of the normal 500, it seems highly plausible that a premature stop codon is causing early termination of translation, leading to a shorter protein sequence.
3. tRNA Error:
- Errors in tRNA can cause issues with protein synthesis, such as misincorporation of amino acids, but these errors are generally less likely to result in a consistently truncated protein length directly.
- tRNA errors are more likely to cause point mutations or misfolding rather than truncating the entire protein sequence.
### Conclusion and Hypothesis
Based on the data provided:
- The gene and mRNA lengths are normal, so the initial steps of gene expression (transcription) are likely unaffected.
- The significant reduction in amino acids from 500 to 283 strongly indicates a truncation during translation.
Hypothesis: The cause of Lucy's shorter amino acid sequence and potentially nonfunctional ADA enzyme is likely due to a Stop Codon Mutation. This mutation introduces a premature stop codon in the mRNA, causing early termination of the protein synthesis.
Rationale: The normal gene and mRNA lengths paired with a truncated protein sequence align well with the scenario where a premature stop codon is introduced, halting translation prematurely and resulting in a shorter protein product. This would lead to the observed low amino acid count and a nonfunctional ADA enzyme.
Further experiments, such as sequencing Lucy's gene and mRNA, could be conducted to confirm the presence of such a stop codon mutation.
I hope this detailed analysis helps you understand the reasoning behind identifying the premature stop codon as a likely cause of Lucy's ADA enzyme malfunction.
