What genes specifically do is provide instructions for building proteins. Most of the useful things in the body are proteins. Some speed up chemical changes and are known as enzymes. Others convey chemical messages and are known as hormones. Still others attack pathogens and are called antibodies. The largest of all our proteins is called titin, which helps to control muscle elasticity. Its chemical name is 189,819 letters long, which would make it the longest word in the English language except that dictionaries don’t recognize chemical names.
