Testosterone is the male sex hormone. Functions vary due primarily to different attached functional groups. Amino acids are the monomers that condense to form proteins, which are very large molecules with structural and metabolic functions. Structural proteins include keratin, which makes up hair and nails, and collagen fibers, which support many organs. Myosin and actin proteins make up the bulk of muscle.
Enzymes are proteins that act as organic catalysts to speed chemical reactions within cells.
Insulin protein is a hormone that regulates glucose content of blood. Hemoglobin transports oxygen in blood. Proteins embedded in the plasma membrane have varied enzymatic and transport functions. Polarity of the peptide bond permits hydrogen bonding between parts of a polypeptide. Amino acids differ in nature of R group, ranging from single hydrogen to complicated ring compounds.