How useful are proteins?

Just as carbohydrates and lipids can release energy, proteins are just as beneficial.

Broken down into their component amino acids, these also liberate energy during respiration. The list below shows important uses of proteins:

• cell-membrane proteins transport substances across the membrane for processes such as facilitated diffusion and active transport
• enzymes catalyse biochemical reactions, e.g. pepsin breaks down protein into polypeptides
• hormones are passed through the blood and trigger reactions in other parts of the body, e.g. insulin regulates blood sugar
• immuno-proteins, e.g. antibodies are made by lymphocytes and act against antigenic sites on microbes
• structural proteins give strength to organs, e.g. collagen makes tendons tough
• transport proteins, e.g. haemoglobin transports oxygen in the blood
• contractile proteins, e.g. actin and myosin help muscles shorten during contraction
• storage proteins, e.g. aleurone in seeds helps germination, and casein in milk helps supply valuable protein to babies
• buffer proteins, e.g. blood proteins, due to their charge, help maintain the pH of plasma.