The word protein comes from the Greek “proteos”, which means “primary” or “first place”. This gives you an idea of how important proteins are. They are complex molecules made of smaller units called amino acids and play several fundamental roles: structure, function, and regulation of the body’s tissues and organs.
Proteins can be classified based on their shape, whether or not they dissolve in water, by what they do, or in lots of other ways. One of the easiest ways is by function, on what they do:
Antibodies: fight foreign particles protecting your body. Immunoglobulin is a large, Y-shaped protein used by the immune system to identify and neutralize pathogenic bacteria and viruses.
Enzymes: carry out almost all of the chemical reactions that take place in cells, and assist with the creation of new molecules. They are like little machines. Some of them build bigger molecules from smaller blocks, others break bigger molecules down into smaller parts. Whether building or breaking, most enzymes can do this 50 to 5k times per second. Your body makes many different kinds of enzymes to digest the food you eat into molecules that your cells can use. Amylase is a good example. It´s an enzyme made by your saliva glands to help break starch down into sugar. Try this experiment: put a cracker on your tongue and wait. At first, the cracker tastes salty but as your mouth waters, the amylase will start to turn the starch in the cracker into sugar, making it taste sweet.
Messengers: such as some types of hormones, transmit signals to coordinate processes between cells, tissues, and organs. Adrenaline is a hormone that regulates visceral functions (e.g, respiration). It plays an important role in the famous fight-or-flight response, increases blood flow to muscles, the output of the heart, pupil dilation response, and blood sugar level.
Structural components: provide structure and support to your cells. On a larger scale, they allow the body to move. Collagen is a perfect example. It holds different parts of your body together connecting and supporting your muscles, bones, tendons, ligaments, cartilage and even holds your skin together. You can find a great article about collagen at Mind Body Fit
Transport/storage: bind and carry small molecules and atoms within cells and throughout the body. Hemoglobin carries oxygen from your lungs to every single cell in your body.