Activity 1: The Three Dimensional Structures of Proteins

1. Cut 55 inches of wire. Wrap it several turns around a pencil. Compare the results with right-to-left turns and with left-to-right turns, as viewed from the back end of the pencil. The left-to-right coiling simulates how proteins can form a coil that is called an alpha helix. Linus Pauling (our "Story Time" subject) discovered that proteins coil naturally in one direction only (clockwise, as viewed from the rear of the pencil) and the helix is stabilized by hydrogen bonds.

2. Straighten out the wire that you just coiled. Start at one end, leave 3 inches free and then begin wrapping the wire left-to-right around a pencil for 4 turns, stop wrapping for about a half inch, then wrap another section for 4 turns. Repeat until you have 7 sections of coils, each separated by a 0.5 inch gap. Leave about 3 inches free at the other end.

3. Fold the coils and cluster them so that you have the seven coils adjacent to each other. Looking down on it you should see that the coils surround an open space. The free, uncoiled ends protrude from each end.

4.  Use the Sharpie color marker to put a few "hot spots" on portions of each free end.

Explanation:

This simulates how receptor proteins are made. Receptors are very specific. For example, one kind binds one kind of hormone, another kind binds another hormone. Receptor proteins differ in the number of coils in the membrane, the number of "wraps" in each coil, and in the nature of the amino acids in the free ends outside and inside the cell.

The coils clump inside membranes because the amino acids in the coils have no electrical charge and they are attracted to lipid and repelled by water. Water is on the inside and outside of the membrane, but not in it. The free ends contain amino acids with electrical charge, and they are therefore attracted to water and repelled by lipid in the membrane.

The hot spots represent the amino acids that are electrically charged. They provide binding sites for drugs, hormones, neurotransmitters and other chemicals. When binding occurs, either on the outside face of the membrane or the inside face, it puts a new mechanical stress on the coils, which may alter the size of the hole in the center. This acts as a gate mechanism to open or close the pore, which in turn affects whether or not molecules can pass in or out through the cell membrane.