All steroids consist of four interlocking rings. Differ only in nature of side groups. Overhead is cholesterol. Proteins Proteins are the most fundamental units of the cell. Many different proteins exist but all are composed of the same building units.
All proteins contain carbon, hydrogen, nitrogen and oxygen and some contain sulfur.
Proteins are built out of amino acids. Although the number of possible amino acids is unlimited, only 20 acids commonly constitute proteins. In Tryptophan R is very complex. To form a protein, amino acids bond together to form polymers. These can be very complex structures such as bovine insulin.