 Genes generally express their functional effect through the production of proteins , which are complex molecules responsible for most functions in the cell . Proteins are made up of one or more polypeptide chains , each of which is composed of a sequence of amino acids , and the DNA sequence of a gene ( through an RNA intermediate ) is used to produce a specific amino acid sequence . This process begins with the production of an RNA molecule with a sequence matching the gene 's DNA sequence , a process called transcription . 
