Produce a nucleotide sequence with a single base-pair substitution mutation that still produces the same amino acid sequence. Indicate the site of the mutation and explain why the amino acid sequence is not affected.

To produce a nucleotide sequence with a single base-pair substitution mutation that still results in the same amino acid sequence, we need to understand the genetic code and how it is read by the cell. The genetic code is a set of rules that determines how a sequence of nucleotides is translated into a sequence of amino acids during protein synthesis.

Here's how you can go about finding a nucleotide sequence with a substitution mutation that doesn't affect the resulting amino acid sequence:

1. Start with the original sequence: Let's say we have the original DNA sequence: ATG GCA GCT TAA. This sequence codes for a specific amino acid sequence.

2. Determine the site of the mutation: Choose a specific base within the sequence and substitute it with a different base. For example, let's say we choose the 3rd base (G) and replace it with an A, resulting in ATG ACA GCT TAA.

3. Translate the nucleotide sequence into amino acids: Use the genetic code to translate the mutated DNA sequence into the corresponding amino acid sequence. For this, you need to refer to the codon table, which shows which codons (sequences of three nucleotides) code for which amino acids. In our case, both 'GCT' and 'ACT' code for the amino acid alanine.

4. Compare the original and mutated amino acid sequences: In this case, despite the base-pair substitution mutation, both the original and mutated sequences code for the same amino acid sequence. Therefore, the amino acid sequence is unchanged, and the mutation does not affect the resulting protein.

The reason why the amino acid sequence is not affected is because of the degeneracy of the genetic code. The code is redundant, meaning that multiple codons can code for the same amino acid. For example, the amino acid alanine can be encoded by the codons GCT, GCC, GCA, or GCG. This redundancy in the genetic code provides some tolerance to mutations, as long as they occur within the codon degeneracy.

In our example, the base substitution affects the codon GCT, but it still codes for the same amino acid (alanine) because the codon GCA or GCC can also code for alanine. Therefore, even with the mutated nucleotide sequence, the same sequence of amino acids is produced, and the protein's function remains unaffected.

To produce a nucleotide sequence with a single base-pair substitution mutation that still produces the same amino acid sequence, we need to understand the relationship between nucleotides and amino acids.

The relationship between nucleotides and amino acids is governed by the genetic code, which is based on triplets of nucleotides called codons. Each codon corresponds to a specific amino acid or a stop signal.

Let's consider an example with the codon "GAC," which normally codes for the amino acid aspartic acid. The three bases (nucleotides) in this codon are G, A, and C. If we were to mutate one of these bases, we could potentially change the coding amino acid. However, not all base-pair substitutions result in a change in the encoded amino acid.

To find a nucleotide sequence with a single base-pair substitution mutation but the same amino acid sequence, we need to identify a codon where changing one of the nucleotides still codes for the same amino acid.

In this example, let's consider the codon "GAC" that codes for aspartic acid. The second nucleotide, A, can be changed to either T or G without affecting the encoded amino acid. Therefore, we could have the following nucleotide sequences:

1. Original sequence: GAC
2. Substituted sequence 1: GTC
3. Substituted sequence 2: GGC

In both substituted sequences, the codon still codes for aspartic acid. This is because the genetic code is degenerate, meaning that multiple codons can code for the same amino acid. In this case, both GAC and GTC, as well as GAC and GGC, code for aspartic acid. The substitution of one nucleotide does not change the amino acid being specified, allowing the amino acid sequence to remain unaffected.

In summary, we can produce a nucleotide sequence with a single base-pair substitution mutation that still produces the same amino acid sequence by altering a nucleotide within a codon that is degenerate, meaning multiple codons can code for the same amino acid.