And so what must happen to these extra amino acids is they must be broken down. Now, the majority of the breakdown of amino acids occurs inside our liver. But other cells, such as muscle cells, can also break down amino acids. For example, inside our muscle cell, we basically break down branch chain amino acids such as leucine, isoleucine, and valine. So let's take a look at how we actually break down amino acids. Now, we have different ways by which we break down different amino acids, but let's begin by focusing on this two step process here.