 The sequence of nucleotides in a gene is read and translated by a cell to produce a chain of amino acids which in turn folds into a protein . The order of amino acids in a protein corresponds to the order of nucleotides in the gene . This relationship between nucleotide sequence and amino acid sequence is known as the genetic code . The amino acids in a protein determine how it folds into its unique three @-@ dimensional shape , a structure that is ultimately responsible for the protein 's function . Proteins carry out many of the functions needed for cells to live . A change to the DNA in a gene can alter a protein 's amino acid sequence , thereby changing its shape and function and rendering the protein ineffective or even malignant ( e.g. sickle cell anemia ) . Changes to genes are called mutations . 
