Some of the phopholipids are better known as lecithins. Lecithins are found in cell membranes and also help in the emulsification of fats. Steroids are arranged as interlocking rings of carbon. They often serve as hormones such as estradiol, progesterone, testosterone, cortisol , etc. Cholesterol is also a steroid made in our body and forms part of the cell membrane .
Cholesterol has several uses, one is for the manufacture of vitamin D .
Proteins Proteins are polymers made up of amino acids . An amino acid is a short carbon skeleton that contains an amino group and a carboxylic acid group. When two amino acids form a bond by removal of water a peptide bond is formed that unites these amino acids into a dipeptide. A polypeptide chains refers to several peptide bonds thus to many amino acids linked together. A specific polypeptide is composed of a specific sequence of amino acids bonded end to end.