Summary
Highlights
A mutation is defined as a change in the DNA base sequence. These changes occur spontaneously, especially during DNA duplication before cell division. Factors that increase the risk of mutations include carcinogens (harmful chemicals in things like cigarette smoke) and certain types of radiation (like x-rays or gamma rays). It's important to remember these factors only increase the risk, they don't guarantee a mutation.
DNA is made of sequences of bases, where every three bases (a triplet or codon) code for a specific amino acid. A chain of amino acids folds to form a protein. If a mutation changes even one base, it can alter the amino acid coded for, leading to a different sequence of amino acids and a different protein shape or function. For example, in an enzyme, this could change the active site, preventing it from binding to its substrate.
Most mutations don't have a significant effect. This is often because they only slightly alter a protein, allowing it to still function effectively. Additionally, many mutations occur in 'non-coding DNA,' which isn't part of a gene and therefore doesn't code for a protein. While much of this non-coding DNA's purpose is unknown, some of it regulates gene expression, determining whether genes are turned on or off.
There are three specific types of mutations: substitutions, insertions, and deletions. A substitution occurs when one base is changed to another. This can alter the codon and, consequently, the amino acid it codes for.
An insertion mutation involves an extra base being added into the DNA sequence. This is typically more impactful than a substitution because it shifts all subsequent bases along by one, altering all subsequent codons. This leads to a completely different amino acid chain from that point onward.
A deletion mutation is when a base is removed from the DNA sequence. Similar to an insertion, a deletion causes all subsequent bases to shift, altering all subsequent codons and leading to significant changes in the amino acid chain.