The best known steroid is cholesterol. Too much cholesterol causes clogging of the arteries, but in the right amount it is very useful. The proteins in our bodies are made of 20 different amino acids strung together like beads on a string. The differences in amino acids are in the 20 different types of R groups. Basic Amino Acid Structure Formation of a Peptide Bond Two amino acids can combine, with the carboxyl of one attaching to the amino group of the other.
Water is removed.
The hydrophobic amino acids are likely to be imbedded in other hydrophobic structures, such as the interiors of membranes or the hydrophobic side groups of another part of the same protein. To cross a membrane a protein must have a stretch of 20 to 25 amino acids which are mostly hydrophobic. The following tables show the 2 groups of amino acids found in proteins. The R groups are shown on the left side. The common structures are encircled with a box.