Enzymes, hormones, structural parts are all made of proteins. Muscle tissue, hair, nails are also protein. Enzymes are organic catalysts are their importance lies in the fact they allow chemical reactions to occur at a rapid pace at body temperature. This allows may important chemical reactions in the body to proceed like digestion, respiration, the break down of hydrogen peroxide in cells, to name a few. Hormones, are chemical messengers that affect target organs in the body. For instance, growth hormone will cause increased cell division in bones during puberty. Histones are important proteins that DNA is coiled around in the nucleus. Eating a diet that includes proteins will provide amino acids which are used by living things to produce protein molecules that the body needs to function.
An important function of proteins is metabolic regulation: for instance, many hormones, like insulin, parathormone regulate metabolism. These proteins are called functional proteins.
The proteins could supply energy when glucose or fats are in low supply.
Myosin and actin are called contractile proteins because they help in contraction of muscles
Collagen provides rigidity and it is sustaining the tissues and organs.