Proteins have numerous functions within living things, including the following:
They help form many of the structural features of the body including hair, nails and muscles. Proteins are a major structural component of cells and cell membranes.
They aid in transporting materials across cellular membranes. An example would be the uptake of glucose into cells from the bloodstream. We will return to this important ability when we discuss the resistance of cancer cells to chemotherapy agents.
They act as biological catalysts. A large group of proteins, known as enzymes, are able to speed up chemical reactions that are necessary for cells to work properly. For example, there are numerous enzymes that are involved in breaking down the food we eat and making the nutrients available.
Interactions between cells are very important in maintaining the organization and function of cells and organs. Proteins are often responsible for maintaining contact between adjacent cells and between cells and their local environment. A good example would be the cell:cell interactions that keep the cells in our skin held closely together. These interactions are dependent on proteins from neighboring cells binding tightly to each other. As we will see, alterations in these interactions are required for the development of metastatic cancer.
Proteins work to control the activity of cells, including decisions regarding cell division. Cancer cells invariably have defects in these types of proteins. We will return to these proteins in detail when we talk about the regulation of cell division.
Many hormones, signals that travel through the body to change the behavior of cells and organs, are composed of protein. Shown below is insulin, a small protein hormone that regulates the uptake of glucose from the bloodstream.
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