Proteins are very large molecules that make up more than half of the dry matter of cells. They are some 2 to 20 times bigger than other molecules in cells. Proteins often determine the shape and structure of cells and they also have two very important functions:

• Recognizing and interacting with other molecules

• Promoting reactions between other chemicals

What are proteins made of?

Much like a string of pearls, a protein is built up from repeating units - in this case smaller molecules called "amino acids." There are 20 such amino acids in the body. Nine of these amino acids cannot be made in the human body. These nine have to be acquired through eating certain foods, such as meat and certain vegetables. 

Proteins differ in the number and sequence of amino acids that they contain. That's where the information code is.

Why is the number of amino acids in a protein important?

Differences in the number and order of amino acids present create different proteins. How many different proteins could you make if you used 4 amino acids per protein? There are 20 amino acids, and each could be positioned any place in the chain. This would create 204 (that's 20 x 20 x 20 x 20) number of patterns. But because proteins have many more amino acids than just four, on the order of 300 amino acids or so, the total possibilities are huge (20300)(that's 20 times itself 300 times). Thus, if you want molecules that contain a lot of "information," proteins are ideal molecules. All cells, of all plant and animal species, depend on proteins to carry information and to do the many kinds of jobs that cells have to do.

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