Genes contain instructions for the making proteins. Genes are inherited from parents; each parent contributes one copy of each gene to a child. Deoxyribonucleic acid makes up genes, and genes make up chromosomes.
Cells make proteins all the time, but not all proteins are being made all the time. Some genes are turned off because their products are not needed at the time.
When a cell decides to make a certain protein, the segment of DNA containing the gene coding for the specific protein is transcribed into a form that can leave the cell's nucleus. This form is called messenger RNA. This strand of mRNA travels to a structure called a ribosome. Transporters called transfer RNA carry individual units called amino acids, the building blocks of proteins, to the ribosome. Each tRNA carries a different amino acid. The tRNA matches up with a section of the mRNA strand and leaves behind its amino acid load. The sequence of amino acids joined together forms the protein.