A point mutation that changes a single nucleotide in a gene but does not alter the amino acid sequence of the protein is called a:

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Silent mutation. A silent mutation (also called a synonymous mutation) is a point mutation that changes a nucleotide in the DNA sequence but does not change the amino acid specified by the codon. This is possible because the genetic code is degenerate (redundant) - most amino acids are encoded by more than one codon. For example, both GCU and GCC code for alanine, so a mutation that changes the third position of the codon from U to C would not affect the protein. Silent mutations are considered neutral with respect to natural selection because they do not alter protein function.

A missense mutation changes a nucleotide in a way that results in a different amino acid being incorporated into the protein. Depending on the location and the nature of the amino acid change, missense mutations can be harmless, harmful, or even beneficial. Sickle cell disease, for example, is caused by a single missense mutation in the hemoglobin gene. A nonsense mutation changes a codon that normally specifies an amino acid into a premature stop codon, resulting in a truncated and usually nonfunctional protein. A frameshift mutation involves the insertion or deletion of nucleotides (not in multiples of three), which shifts the reading frame and alters every amino acid downstream of the mutation.

Understanding the different types of mutations and their potential effects on protein structure and function is essential for the CLEP Biology exam. The impact of a mutation depends on several factors: where it occurs in the gene, whether it changes the amino acid sequence, how it affects protein folding and function, and whether it occurs in a critical region of the protein. This knowledge connects to broader topics including evolution (mutations as the ultimate source of genetic variation), genetics (inherited disorders), and molecular biology (gene expression and regulation).

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