Your body is made up of billions of tiny cells, working all the time to stay alive by fulfilling different jobs. Each job is done by several small molecules, called proteins. All of the proteins that the cell needs are “coded” by DNA, a long molecule found in the center of each cell.
DNA is made up four different bases, or letters, A, T, C, and G, repeated in a random order. A strand of DNA consists of 3.3 billion bases. To put it in perspective, that many letters would take up 3 gigabytes of storage space in a computer. Through a complex process, some small sequences of letters can be converted into a functional protein. These portions of DNA are called genes. Humans have approximately 20,000 genes scattered throughout the genome.
The DNA in each of your cells have the exact same sequence of bases. The DNA sequence of any two humans is 99.9% identical, meaning that some bases are changed. For example, where one person may have the base ‘A’ at a certain part of the sequence, another may have the base ‘T’ or ‘C’ or ‘G’ in the same spot. This 0.1% difference accounts for 3 million bases, and the small differences are called variants.
Variation in a single base is called a Single Nucleotide Polymorphism, better known as a SNP (pronounced “snip”). Depending on the base at that position, the resulting protein may have a slightly different structure which changes how well it does its job.
The role of proteins