Question

Explain why a nonsynonymous mutation in an exon is likely to have a greater potential impact on evolution than a synonymous mutation in an exon.

Short answer

Nonsynonymous mutations in an exon lead to changes in the amino acid sequence of proteins, potentially affecting their structure and function significantly, thereby impacting an organism's fitness and survival. Conversely, synonymous mutations do not result in a change in the amino acid sequence, hence are less likely to influence the evolution of a species. Thus, a nonsynonymous mutation is likely to have a greater potential impact on evolution than a synonymous mutation.

Step-by-step solution

Understanding Mutations

Firstly, it is important to grasp what both nonsynonymous and synonymous mutations are. Nonsynonymous mutations in an exon result in a change in the amino acid sequence of a protein, this is due to the fact that the nucleotide alteration leads to a different codon which codes for a different amino acid. Conversely, synonymous mutations are those in which the nucleotide change does not result in a different amino acid being incorporated into the protein, hence the name 'silent' mutations.

Effect of Nonsynonymous Mutations on Protein Function

The reason nonsynonymous mutations have a greater potential impact on evolution is due to their ability to change the amino acid sequence of proteins. Proteins, being the functional units in cells, determine the phenotype of an organism. Therefore, a change in the amino acid sequence might change the protein's structure and/or function, which can significantly impact an organism's fitness and survival.

Effect of Synonymous Mutations on Protein Function

On the other hand, since synonymous mutations do not result in a change in the amino acid sequence of a protein, they are less likely to alter protein function and therefore less likely to influence the evolution of a species. However, it should be noted that this is not always the case as synonymous mutations can also affect gene expression and protein folding.

Comparing the Evolutionary Impact

In general, nonsynonymous mutations are more likely to have a greater potential impact on evolution than synonymous mutations because they directly change the protein's amino acid sequence and thus its structure and function. While synonymous mutations can sometimes impact gene expression and protein function, these effects tend to be more subtle and less common.

Key concepts

Genetic Mutations

Imagine the genetic code as an instruction manual for building living creatures. Genetic mutations are essentially typos in this manual. Sometimes these typos are harmless; other times, they're more like accidentally replacing 'screw' with 'glue' in assembly instructions for a chair—you'll end up with something quite different than intended.

Nonsynonymous mutations are the 'game changers' in this scenario as they alter the protein 'blueprint' in a way that could potentially change the final 'product'—the protein's structure and function. They change the amino acid that is to be included in a protein by altering the DNA sequence of the genes, thus changing the message in the instruction manual. Synonymous mutations, on the other hand, are 'silent' because they don't change the amino acid sequence despite a change in the genetic code. They're like changing the font in the manual but not the instructions themselves.

Protein Function

Proteins are the 'doers' in the body—think of them as workers on a construction site. Each protein has a specific job, from building cellular structures to defending the body against pathogens.

A protein's function is determined by its shape, which is, in turn, determined by the sequence of amino acids it contains. If a nonsynonymous mutation alters an amino acid, it could be like giving a construction worker a hammer instead of a wrench—it changes how they can do their job. This could lead to significant physical alterations in an organism, potentially even influencing survival and reproduction.

Evolutionary Impact

Evolution is like a long, slow talent show, where traits that are beneficial might help an organism 'win' by having more offspring. Nonsynonymous mutations can introduce new traits by altering protein functions. If those new traits are useful, they may be passed on and become more common in a population over time.

Changes resulting from such mutations can thus drive evolutionary changes. However, not all alterations are beneficial; some might be harmful or neutral. The evolutionary impact of a mutation is influenced by how it affects an organism's ability to survive and reproduce in its environment.

Exon Functions

Exons can be thought of as the highlighted, important parts of the genetic instruction manual—the parts that actually get 'read out loud' to make proteins. The rest of the DNA, called introns, is like the pages that get skipped over.

When a nonsynonymous mutation occurs in an exon, it changes the section being read, which directly affects the protein produced. It's as if you change a crucial step in the instructions for assembling a toy. This change in the final product might make the toy more entertaining or cause it to fall apart—akin to the range of possible impacts on a protein's function.

Amino Acid Sequence

Amino acids are the building blocks of proteins—think of them like different shaped Lego pieces. The order in which they are put together in a protein dictates the final shape of the protein.

If a nonsynonymous mutation swaps one amino acid for another, it can be compared to switching a square Lego piece for a round one in a model. This can either be inconsequential or result in a completely different structure. The protein's ability to perform its job is directly tied to the sequence of these molecular 'Legos,' and any change to the sequence can have wide-ranging effects on the organism as a whole.