Human Nutrition 3(3+0)

Lesson 17 : Proteins

Functions

Protein provides 4 calories per gram and it is an important source of energy for the body, when carbohydrates and fats are not available. In addition, the body uses the amino acids in the protein to manufacture its own proteins. The proteins synthesized by the body perform a variety of important physiological functions:

 

• Production and maintenance of structural proteins: The body manufactures several structural proteins, such as myosin, actin, collagen, elastin and keratin that maintain the strength and integrity of muscles, connective tissues (ligaments and tendons), hair, skin, and nails.

• Production of enzymes and hormones: Enzymes are compounds that catalyze chemical reactions in the body, are made from proteins. In addition, the hormones involved in blood sugar regulation (insulin and glucagon) as well as the thyroid hormones are synthesized from proteins.

• Production of transport proteins and lipoproteins: Certain proteins are used by the body to carry various substances to body tissues. These transport proteins include hemoglobin (carries oxygen), transferrin (carries iron), ceruloplasmin (carries copper), retinol-binding protein (carries vitamin A), albumin and transthyretin (both carry other proteins). Lipoproteins participate in the transportation of fat and cholesterol.

• Maintenance of proper fluid balance: Proteins participate in the maintenance of osmotic pressure, which controls the amount of water that is found inside of cells.

 

Source: WARDLAW et al.

Figure: Blood proteins are important for maintaining the body’s fluid balance. Due to insufficient protein in the bloodstream, edema develops.

Production of antibodies: Antibodies made up of proteins, play an important role in the immune system by attaching to antigens (viruses, bacteria, or other foreign invaders), thereby inactivating the antigens and making them more visible to the immune cells (called macrophages) that destroy antigens.

• Maintenance of proper acid-base balance: Due to their ability to combine with both acidic and basic substances, proteins help to maintain the normal acid-base balance in the body.