The DNA sequence of a gene determines the amino acid sequence of the protein that it encodes. This is because the DNA sequence is transcribed into an RNA molecule, which is then translated into a protein. The genetic code is a set of rules that specifies which amino acid is encoded by each codon, which is a sequence of three nucleotides.

The amino acid sequence of a protein determines its structure and function. The structure of a protein is determined by the interactions between its amino acids. These interactions can cause the protein to fold into a specific shape, which is essential for its function. The function of a protein is determined by its shape and its chemical properties. For example, some proteins are enzymes, which catalyze chemical reactions, while others are structural proteins, which provide support and strength to cells.

Therefore, the DNA sequence of a gene ultimately determines the function of the protein that it encodes. This is a fundamental principle of molecular biology.