For example, some proteins act as biological catalysts, speeding up different types of biochemical reactions that are used that are carried out by our cells. For example, the production of ATP involves many different types of enzymes, many different types of biological catalysts. Now, proteins also function in transport. For example, we know that hemoglobin is a type of protein that transports oxygen from the lungs and to the tissues and cells of our body. And oxygen is necessary to basically produce ATP. Now, proteins can also be embedded inside cell membranes.