When the amino acid sequences of insulin isolated from different organisms were determined, differences were noted. For example, alanine was substituted for threonine, serine for glycine, and valine for isoleucine at corresponding positions in the protein. List the single-base changes that could occur in codons of the genetic code to produce these amino acid changes.

Verified step by step guidance

1. Identify the original and substituted amino acids: alanine (Ala) for threonine (Thr), serine (Ser) for glycine (Gly), and valine (Val) for isoleucine (Ile).
2. Determine the codons for each of the original amino acids: Thr (ACU, ACC, ACA, ACG), Gly (GGU, GGC, GGA, GGG), Ile (AUU, AUC, AUA).
3. Determine the codons for each of the substituted amino acids: Ala (GCU, GCC, GCA, GCG), Ser (UCU, UCC, UCA, UCG, AGU, AGC), Val (GUU, GUC, GUA, GUG).
4. Identify possible single-base changes in the codons that could result in the amino acid substitutions. For example, a change from ACU (Thr) to GCU (Ala) involves a single base change from A to G.
5. Repeat the process for each amino acid substitution, considering all possible codon changes that involve a single nucleotide alteration.

Key Concepts

Genetic Code

The genetic code is a set of rules that defines how the sequence of nucleotides in DNA or RNA translates into the sequence of amino acids in proteins. It consists of codons, which are triplets of nucleotides, each corresponding to a specific amino acid or a stop signal. Understanding the genetic code is essential for determining how mutations can lead to changes in amino acid sequences.

Point Mutations

Point mutations are changes in a single nucleotide base pair in the DNA sequence. These mutations can lead to different amino acids being incorporated into proteins, depending on the nature of the change. For example, a transition mutation (purine to purine or pyrimidine to pyrimidine) or a transversion mutation (purine to pyrimidine or vice versa) can result in the substitutions noted in the insulin sequences.

Amino Acid Substitution

Amino acid substitution occurs when one amino acid in a protein is replaced by another due to changes in the corresponding codons. This can affect the protein's structure and function, depending on the properties of the substituted amino acids. Identifying the specific codon changes that lead to these substitutions is crucial for understanding the genetic basis of protein variation across different organisms.