Protein Structure
Proteins are long chains of amino acids. Only twenty amino acids in various combinations form proteins, so for simplicity, each amino acid is often represented by a letter of the alphabet. Therefore, a protein can be written as a sequence such as MALWMRLLPL. These amino acids are the beginning of the protein insulin. Insulin is a small protein: here is it's complete list of amino acids:
MALWMRLLPL LALLALWGPD PAAAFVNQHL
CGSHLVEALY LVCGERGFFY TPKTRREAED
LQVGQVELGG GPGAGSLQPL ALEGSLQKRG
Many proteins are ten, twenty, or a hundred times bigger than insulin. But all proteins are chains of the same 20 amino acids. There are hundreds of thousands of proteins, each different in the sequence of its amino acids.
If you know a protein's sequence of amino acids, you can identify it. This is the basis of protein identification by mass spectrometry.
Within cells, proteins fold these one-dimensional chains into an amazing variety of three-dimensional structures. These 3D structures allow proteins to perform their wide range of functions. You can get an idea of the wide variety of protein structures by following the "Protein pictures" related links on the left.
Much of protein science is devoted to learning these 3D structures and how to predict a protein's function from its structure. A major computational biology problem is predicting the 3D structure from the 1D structure. . You can also participate in the computational biology of protein folding with the "folding@home" project.
Protein Functions
Proteins work together in pathways — sequences of chemical reactions — to perform a wide variety of functions:
- Metabolism — proteins mediate chemical reactions that use oxygen to burn food for energy. These pathways are complex but well studied. The related links show maps of thousands of proteins in the metabolic pathways.
- Signaling — hormones are proteins that signal between cells usually in the blood. Proteins also send signal from one nerve cell to another. Signaling pathways, however, are usually interactions among proteins within a cell.
- Regulation — proteins called enzymes control chemical reactions in cells. Proteins also form gateways in cellular membranes to control what passes into or out of a cell.
- Cellular structure — proteins define cell shape and form.
- Transportation — proteins move oxygen, sugar, nutrients and wastes into and around cells. They also move other proteins from where they are made to where they are used.
- Movement - proteins contract muscles and move cells.
- DNA Transcription — proteins turn genes on and off.
- Immune System Functions - special proteins identify germs and other foreign substances and mark them for destruction.
