Session 2 -- Page 1
July 5, 2000

Polymers

The first principle of molecular biology is this:

The most important substances in living things are polymers.

In other words,
what distinguishes living from non-living things are polymers.

Put another way,
"Polymers 'R Us".

The reason that polymers are central to life is that they are required for all the activities that living things do. For example:

• Polymers are responsible for directing the chemical reactions that go on inside living cells. The manufacture of all of the substances within cells, the breakdown of all cellular materials, and the transformation of substances from one form into another are processes that are choreographed by polymers.
• Polymers keep unwanted chemicals from entering cells, bring required materials in, and throw out poisons. In other words, polymers act as molecular gatekeepers, guarding cells from threatening substances. They also behave like garbage haulers and cleanup crews, making sure that we are not harmed by our own wastes.
• Polymers allow cells to recognize and react to substances that are around them. Polymers therefore form the "sense organs" of cells - their "eyes" and "ears" - allowing living things to be aware of their environment.
• Polymers are the driving force behind cell movement. They form molecular motors that permit the cell and its internal contents to move about.
• Polymers make up the bulk of the structural elements -- the bricks and mortar -- of all cells. Those structures that are not directly made out of polymers, are constructed by polymers.
• Polymers carry the instructions that organisms use to make other polymers, as well as for the manufacture of additional copies of themselves. Those polymers that are capable of replication permit the instructions of life to be passed on from one generation to another.

Definition of a Polymer
Since polymers are vital to life, it's important to understand them as fully as possible. An essential question is: Exactly what are polymers?

The word means "many parts", and most polymers -- including all those of biological origin -- are large molecules made out of many little molecules ("monomers") joined end to end in long chains.

You can being to understand something about the properties of polymers by playing with a set of plastic beads. A cross section through a typical bead in the set is shown in the illustration at the right. It is a small plastic sphere with a hole at one end and a little knob at the other. Each bead represents one monomer.

This bead can be joined to any of the others by inserting its knob into the hole of another. Once the connection has been made, the parts hold together fairly securely. You can create a longer chain by connecting several of the units together. It is this chain that is a model of a polymer.

Take a close look at the illustration at the right. Better yet, get a set of beads like these and join them together. Several properties of the chains that you make will become apparent.