Genes code for the instructions that tell a cell how to make a specific protein. The genetic code is a set of rules that defines how the four-letter code of DNA is translated into the 20-letter code of amino acids, which are the building blocks of proteins. Each genes code uses the four nucleotide bases of DNA: adenine (A), cytosine (C), guanine (G), and thymine (T) in various ways to spell out three-letter “codons” that specify which amino acid is needed at each position within a protein. During the process of transcription, the information stored in a genes DNA is passed to a similar molecule called RNA (ribonucleic acid) in the cell nucleus. The type of RNA that contains the information for making a protein is called messenger RNA (mRNA) because it carries the information, or message, from the DNA out of the nucleus into the cytoplasm. Translation, the second step in getting from a gene to a protein, takes place in the cytoplasm. The mRNA interacts with a specialized complex called a ribosome, which "reads" the sequence of mRNA nucleotides. Each sequence of three nucleotides, called a codon, usually codes for one particular amino acid. A type of RNA called transfer RNA (tRNA) assembles the protein, one amino acid at a time.

In summary, genes code for the instructions that tell a cell how to make a specific protein. The genetic code is a set of rules that defines how the four-letter code of DNA is translated into the 20-letter code of amino acids, which are the building blocks of proteins. Each genes code uses the four nucleotide bases of DNA in various ways to spell out three-letter “codons” that specify which amino acid is needed at each position within a protein. During the process of transcription, the information stored in a genes DNA is passed to a similar molecule called RNA in the cell nucleus. Translation, the second step in getting from a gene to a protein, takes place in the cytoplasm. The mRNA interacts with a specialized complex called a ribosome, which "reads" the sequence of mRNA nucleotides. Each sequence of three nucleotides, called a codon, usually codes for one particular amino acid. A type of RNA called transfer RNA (tRNA) assembles the protein, one amino acid at a time.