Question
Cystic fibrosis is caused by a mutation in a gene involved in plasma membranes. The image shows the amino acid sequences coded by a normal and a mutated gene.
Normal Sequence: VALINE-HISTIDINE-LEUCINE-THREONINE-PROLINE-GLUTAMIC ACID-GLUTAMIC ACID
Mutated Sequence: VALINE-HISTIDINE-LEUCINE-THREONINE--ALANINE-TRYPTOPHAN
Analyze the sequences and select the option which best describes the change in the DNA sequence of the gene coding for the mutated protein.
A base pair is added in the DNA sequence.
A base pair is translocated in the DNA sequence.
A base pair is deleted in the DNA sequence.
A base pair is replaced in the DNA sequence.
Normal Sequence: VALINE-HISTIDINE-LEUCINE-THREONINE-PROLINE-GLUTAMIC ACID-GLUTAMIC ACID
Mutated Sequence: VALINE-HISTIDINE-LEUCINE-THREONINE--ALANINE-TRYPTOPHAN
Analyze the sequences and select the option which best describes the change in the DNA sequence of the gene coding for the mutated protein.
A base pair is added in the DNA sequence.
A base pair is translocated in the DNA sequence.
A base pair is deleted in the DNA sequence.
A base pair is replaced in the DNA sequence.
Answers
GPT-4o mini
To determine the type of mutation that has occurred in the gene coding for the mutated protein, we need to analyze the sequences provided.
The normal amino acid sequence is:
- VALINE-HISTIDINE-LEUCINE-THREONINE-PROLINE-GLUTAMIC ACID-GLUTAMIC ACID
The mutated amino acid sequence is:
- VALINE-HISTIDINE-LEUCINE-THREONINE-ALANINE-TRYPTOPHAN
Comparing the two sequences, we observe the following:
1. The first four amino acids (VALINE-HISTIDINE-LEUCINE-THREONINE) are the same in both sequences.
2. In the normal sequence, the fifth amino acid is PROLINE, while in the mutated sequence it is ALANINE.
3. The sixth amino acid in the normal sequence is GLUTAMIC ACID, but in the mutated sequence, it is TRYPTOPHAN.
Since two amino acids are missing from the mutated sequence and the sequences are shorter, it indicates that there is either a deletion or replacement of base pairs in the DNA sequence. To have ALANINE and TRYTPTOPHAN in the place of PROLINE and GLUTAMIC ACID suggests that there have been changes in the coding sequence.
Given the options:
- **A base pair is added in the DNA sequence.** (This does not apply as we see a shortening of the sequence.)
- **A base pair is translocated in the DNA sequence.** (Not applicable based on the comparison of sequences.)
- **A base pair is deleted in the DNA sequence.** (This could explain the absence of the last two amino acids.)
- **A base pair is replaced in the DNA sequence.** (There are amino acids that have been completely changed from what they should be, rather than just a single replacement.)
The most fitting explanation for the differences in the sequences is that **a base pair is deleted in the DNA sequence**, as there are two amino acids (PROLINE and GLUTAMIC ACID) missing in the mutated sequence, indicating a loss of coding information.
Therefore, the correct answer is:
**A base pair is deleted in the DNA sequence.**
The normal amino acid sequence is:
- VALINE-HISTIDINE-LEUCINE-THREONINE-PROLINE-GLUTAMIC ACID-GLUTAMIC ACID
The mutated amino acid sequence is:
- VALINE-HISTIDINE-LEUCINE-THREONINE-ALANINE-TRYPTOPHAN
Comparing the two sequences, we observe the following:
1. The first four amino acids (VALINE-HISTIDINE-LEUCINE-THREONINE) are the same in both sequences.
2. In the normal sequence, the fifth amino acid is PROLINE, while in the mutated sequence it is ALANINE.
3. The sixth amino acid in the normal sequence is GLUTAMIC ACID, but in the mutated sequence, it is TRYPTOPHAN.
Since two amino acids are missing from the mutated sequence and the sequences are shorter, it indicates that there is either a deletion or replacement of base pairs in the DNA sequence. To have ALANINE and TRYTPTOPHAN in the place of PROLINE and GLUTAMIC ACID suggests that there have been changes in the coding sequence.
Given the options:
- **A base pair is added in the DNA sequence.** (This does not apply as we see a shortening of the sequence.)
- **A base pair is translocated in the DNA sequence.** (Not applicable based on the comparison of sequences.)
- **A base pair is deleted in the DNA sequence.** (This could explain the absence of the last two amino acids.)
- **A base pair is replaced in the DNA sequence.** (There are amino acids that have been completely changed from what they should be, rather than just a single replacement.)
The most fitting explanation for the differences in the sequences is that **a base pair is deleted in the DNA sequence**, as there are two amino acids (PROLINE and GLUTAMIC ACID) missing in the mutated sequence, indicating a loss of coding information.
Therefore, the correct answer is:
**A base pair is deleted in the DNA sequence.**