Most of a cell’s functions are carried out by proteins. Proteins embedded in the cell membrane transport molecules into and out of the cell. Proteins catalyze and regulate chemical reactions in the metabolic network. Proteins even build other proteins. In many ways, a cell’s capabilities are determined by the proteins it can build.
Templates for all of the proteins that a cell can build are stored in genes in the cell’s genome. Each gene acts as a template for building a single protein. Since human cells contain ~20,000 genes, a human cell can build ~20,000 different types of proteins.
Genes consist of long strands of nucleotides in the form of a DNA or RNA molecule. Each sequence of three nucleotides in the strand form a codon that selectively binds with one specific amino acid. This is how a strand of nucleotides can encode the strand of amino acids making up a protein molecule.
Players design a cell’s genome by selecting which genes to include. Adding more genes to the genome will give the cell more capabilities; however, increasing the size of the genome will also make it more costly to duplicate the genome when it is time for the cell to reproduce.