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Assembly of Stuctures

©2000 Timothy Paustian, University of Wisconsin-Madison

Often, once the polymers are formed they will correctly self assemble into the macromolecular structures. The information necessary for biopolymers to come together into the structures of the cells is encoded in their primary sequence. Here are a few examples

• When double stranded DNA is boiled in water it, it will dissociate into two separate strands. If the solution is slowly cooled, the complementary strands will find each other and zip back together in the proper sequence.

• Adding lipids to pure water will cause them to self assemble into a sphere composed of an inside and an outside with a lipid bilayer separating the two.

• During the synthesis of proteins the growing amino acid chain will start to assemble into its correct structure.

• The 52 proteins and 3 RNAs that make up the ribosome will self assemble into a functional ribosome in a test tube if they are added in the correct order.

The take home message is that many cell polymers know how to assemble into structures. From an evolutionary standpoint this makes sense. Primitive self replicating molecules probably organized themselves into structures using the simplest mechanism possible - self assembly. As more complex organisms evolved, this method continued to hold sway due to its elegance.

After saying all of this, I am now going to contradict myself. Recent work has shown there are proteins in high concentration that seem to assist many of these assembly processes, guiding the polymers down the correct path, destroying aberrant assemblies and increasing efficiency. As higher life forms (bacteria) evolved it became worthwhile to create proteins to increase the chances of getting successful macromolecules built. The term molecular chaperons has been coined to describe these molecules. It seems as if all living organisms contain proteins that carry out these guiding functions.

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