How does a change in one nucleotide in one triplet code can change the nature of a protein and therefore the form of the trait ?
I believe this has something to do with mutations. I know that mutation may result from errors in DNA replication or recombination, or physical or chemical agents called mutagens.
I'm asked to use hemoglobin molecule as an example, however I'm not sure how this relates.
You are correct that mutations play a key role in causing changes in proteins and traits. In order to understand how a change in one nucleotide can affect a protein and the associated trait, let's take the example of the hemoglobin molecule.
Hemoglobin is a protein that carries oxygen in red blood cells. Its structure is made up of four protein chains, each containing a large number of amino acids. The instructions for building these protein chains are coded in the DNA of our cells. The DNA sequence is divided into sets of three nucleotides called triplets or codons, and each triplet codes for a specific amino acid in the protein chain.
Now, let's consider a specific mutation involving a change in a single nucleotide in one triplet code in the DNA sequence. This change can result in three different scenarios:
1. Silent Mutation: Sometimes, a change in one nucleotide does not affect the protein at all. This occurs when the altered codon still codes for the same amino acid as before. In this case, there would be no change in the protein's structure or function, and the trait associated with it would remain the same.
2. Missense Mutation: Another possibility is that the mutation changes the codon so that it codes for a different amino acid. This type of mutation is called a missense mutation. The altered amino acid in the protein can affect its structure and function. Depending on the specific location and nature of the amino acid change, the protein may become less efficient or even dysfunctional. This can lead to changes in the trait associated with the protein. For example, in the case of hemoglobin, a missense mutation can cause abnormal folding of the protein, resulting in a condition called sickle cell anemia.
3. Nonsense Mutation: The third scenario occurs when the mutation creates a premature stop codon. This type of mutation is called a nonsense mutation. When a premature stop codon is encountered during protein synthesis, the protein may be truncated, resulting in a shortened or non-functional protein. This can also lead to changes in the associated trait.
Overall, a change in one nucleotide in one triplet code can have various effects on the final protein structure and function, ultimately resulting in changes to the trait associated with that protein.