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\begin{tabular}{|c|c|c|c|}
\hline & Normal Range & Lucy & \\
\hline Gene Length & \begin{tabular}{l}
1,500 \\
base pairs
\end{tabular} & \begin{tabular}{l}
1,500 \\
base pairs
\end{tabular} & Normal \\
\hline mRNA Length & \begin{tabular}{l}
1,500 \\
nucleic acids
\end{tabular} & \begin{tabular}{l}
1,500 \\
nucleic acids
\end{tabular} & Normal \\
\hline Amino Acid Sequence & \begin{tabular}{l}
500 \\
amino acids
\end{tabular} & \begin{tabular}{l}
283 \\
amino acids
\end{tabular} & Low \\
\hline
\end{tabular}

Choose the mutation that you think is causing Lucy's ADA enzyme not to work:

A. Active Site Mutation
B. Stop Codon Mutation
C. tRNA Error

Form a hypothesis and explain your answer. You can revise your hypothesis as you perform more experiments.

Type your answer here: ______________________

Sagot :

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.