Effect of Mutation on Coding by the DNA Segment

The given DNA segment is: ATGACC AGG ACC CCA ACA. Let's analyze the effect of a mutation on the first base of this DNA segment.

No Change in the Sequence
If the first base of the DNA segment is mutated, resulting in a change in the DNA sequence, it is important to consider the genetic code and its degeneracy. The genetic code is a set of rules that specifies how the sequence of nucleotides in DNA is translated into the sequence of amino acids in a protein.

Genetic Code and Amino Acid Translation
The genetic code is read in groups of three nucleotides called codons. Each codon corresponds to a specific amino acid or a stop signal. For example, the codon "ATG" is the start codon, which initiates protein synthesis, and "ACC" corresponds to the amino acid threonine.

Effect of Mutation
If the first base of the DNA segment is mutated, it would result in a change in the first codon. As a result, the first amino acid in the protein sequence would be different.

Explanation of Options
Let's evaluate the given options based on the effect of the mutation:

A) Complete change in the type as well as sequence of amino acids: This option suggests that the mutation would result in a complete change in both the type and sequence of amino acids. However, since only the first base is mutated, it would lead to a change in the first amino acid but not necessarily all subsequent amino acids. Therefore, this option is incorrect.

B) Change in the first amino acid only: This option correctly reflects the effect of the mutation. Changing the first base would alter the first codon, leading to a change in the first amino acid of the protein sequence.

C) No change in the sequence: This option suggests that the mutation would have no effect on the protein sequence. However, since the first base is mutated, it would result in a change in the codon and subsequently the amino acid. Therefore, this option is incorrect.

D) One amino acid less in the protein: This option suggests that the mutation would result in a deletion of one amino acid from the protein sequence. However, a single base mutation is unlikely to cause a deletion of an entire amino acid. Therefore, this option is incorrect.

E) No coding: This option suggests that the mutation would render the DNA segment non-coding. However, a single base mutation is unlikely to completely disrupt the coding potential of the DNA segment. Therefore, this option is incorrect.

Conclusion
Based on the analysis, the correct answer is B) Change in the first amino acid only. The mutation in the first base of the DNA segment would lead to a change in the first codon and subsequently the first amino acid in the protein sequence.