What Is Main Purpose of Protein in Living Things?

Protein is a nutrient your body needs to grow, as well as to support and maintain your life. After water, protein is the most plentiful substance in your body. You might know that your muscles are composed of protein, but the substance, in its various forms, serves in other crucial roles. For example, proteins help cells develop and communicate, act as enzymes and hormones, conduct the transport of nutrients throughout your bloodstream and repair damaged tissue. In other words, you can't live without protein.

Protein's not just about muscle tissue. (Image: chesterf/iStock/Getty Images)

Muscle Mass

The building blocks of proteins are amino acids. Twenty known amino acids link together to form various kinds of protein. Proteins called actin and myosin compose much of your muscle fibers. They slide past each other, forming cross-bridges that allow the muscles to contract. They enable virtually all forms of movement, from blinking your eyes to running, jumping and dancing. Your heart, liver, lungs and most of the organs in your body are made of proteins.

Cell Formation

Every cell in your body has some protein in it. Huge clusters of proteins come together to construct cells, performing such tasks as copying genes during cell division and developing new proteins. Protein receptors on the outside of cells communicate with "partner" proteins within the cell. A "carrier" protein is used to make hemoglobin, the part of your red blood cells that shuttles oxygen throughout your body. Protein is also an important part of your immune system, as it is an essential ingredient in the antibodies your body makes to protect you from infections.

Tissue Maintenance and Repair

You need protein to help your body repair cells and create new ones. Your hair, skin and nails are composed of a type of protein, which also is needed to maintain their integrity, as well as repair and replace tissues. For example, if you fall down and bruise yourself, protein is highly involved in healing your wounds. Proteins also support your body. For example, collagen is a fibrous type of protein in your cartilage and tendons that supports your bones and maintains your skin.

Enzymes and Hormones

Enzymes are proteins that control chemical reactions in your body. Many hormones are essentially "messenger" proteins that tell your cells how to behave. Enzymes in your saliva, stomach and intestines are proteins that aid in digestion. Insulin is an example of a protein that acts as a hormone. Its job is to help move blood sugar into your cells to provide fuel.

Energy Source

As a macronutrient, or a nutrient you need in fairly large quantities, protein can be used by your body as a source of energy. In healthy, well-nourished people, your body will attempt to spare your protein stores before dipping into them. They have important work to do, after all. However, if you don't have enough carbohydrates or fats stored, protein can be used. On the other hand, if you consume more protein than your body needs, it can be stored as fat.