Think about how molecules recognize each other. Proteins that fit well with other molecules, like a hand in a glove, or a key in a lock, can participate in reactions with those molecules. Whether or not a good fit occurs depends on the structure of the protein and of the molecules with which it encounters either inside the cell or on the cell surface.

Remember the illustration of the crumpled sheet of paper?

A protein's function is established by its structure.

In membranes, protein structure affects function in two ways:

1. non-charged parts coil in the membrane,
   acting like an anchor

2. portions of the protein that are attracted to water, stick out both sides of the membrane, available to interact with other molecules

Proteins are so precisely built that a change in only a few amino acids can radically change the structure of proteins and cause major changes in the function. Many of the genetic diseases are caused by miscoding of the sequence of only a few amino acids. Structure of proteins, particularly those in the cell membrane that have signaling functions, can be changed by interaction with molecules in the environment, and their functions become temporarily altered. This may affect how they bind with hormones or drugs or with other molecules.

For more on neat views of 3-D protein structure, click here. When you arrive at the Web page, pick a protein of interest, hit "View Structure", and then Hit "Quick PDB". Use "Help" to see all the cool viewing tricks.