Question

When the amino acid sequences of insulin isolated from different organisms were determined, some differences were noted. For example, alanine was substituted for threonine, serine was substituted for glycine, and valine was substituted for isoleucine at corresponding positions in the protein.

Which of the following single base changes would result in alanine being substituted for threonine?
A) A changed to C in the third position of the codon.
B) C changed to G in the second position of the codon.
C) A changed to G in the first position of the codon.

Answer 1

The correct single base change that would result in alanine being substituted for threonine at the corresponding positions in insulin is C changed to G in the second position of the codon.

Step-by-step explanation:

Which of the following single base changes would result in alanine being substituted for threonine? To answer this question, we must consider the genetic code and how amino acids are coded by mRNA codons. Threonine is coded by the codons ACU, ACC, ACA, and ACG. Alanine, on the other hand, is coded by the codons GCU, GCC, GCA, and GCG. Out of the options given, Option A (A changed to C in the third position of the codon) would not result in alanine because a change in the third position often does not affect the amino acid due to the 'wobble' effect and given threonine's codons do not translate to alanine with just a change at the third position. Option C (A changed to G in the first position of the codon) would also not result in alanine, as it would still encode for threonine or another amino acid but not alanine in the given context. However, Option B (C changed to G in the second position of the codon) could change a threonine codon (ACC) to an alanine codon (GCC).

Answer 2

C) A changed to G in the first position of the codon.

Step-by-step explanation:

In the translation of DNA, triplets or codons of mRNA (a group of three nucleotides) are read according to a genetic code, to build proteins.

Proteins are composed of amino acids. In the translation process, each codon codes for an particular amino acid according to the genetic code as illustrated in the DNA codon table (attached here).

In this table we can see that if the first position of any of the codons coding for Threonine ( ACT, ACC, ACA, ACG) is changed for G, Adenine is going to be encoded instead of threonine.