Polymer

A polymer is a long, repeating chain of atoms, formed through the linkage of many molecules called monomers। The monomers can be identical, or they can have one or more substituted chemical groups. These differences between monomers can affect properties such as solubility, flexibility, or strength. In proteins, these differences can give the polymer the ability to preferentially adopt one conformation over another, as opposed to adopting a random coil . Although most polymers are organic (based on carbon chains), there are also many inorganic polymers.
The term polymer covers a large, diverse group of molecules, including substances from proteins to high-strength kevlar fibres. A key feature that distinguishes polymers from other large molecules is the repetition of units of atoms (monomers) in their chains. This occurs during polymerization, in which many monomer molecules link to each other. For example, the formation of polyethene involves thousands of ethene molecules bonding together to form a chain of repeating -CH2- units:

Polymers are often named in terms of their monomer units, for example polyethylene is represented by:

Because polymers are distinguished by their constituent monomers, polymer chains within a substance are often not of equal length. This is unlike other molecules in which every atom is acounted for, each molecule having a set molecular mass. Differing chain lengths occur because polymer chains terminate during polymerization after random intervals of chain lengthening (propagation).
Proteins are polymers of amino acids. From a dozen to some hundred of the (about) twenty different monomers form the chain, the sequence of monomers determining the shape and activity of the final protein. But there are active regions, surrounded by, as is believed now (Aug 2003), structural regions, whose sole role is to expose the active region(s) (there may be more than one on a given protein). So the absolute sequence of amino acids is not important, as long as the active regions are expressed (being accessible from the outside) properly. Also, whereas the formation of polyethylene occurs spontaneously given the right conditions, the manufacture of biopolymers such as proteins and nucleic acids requires the help of catalysts (substances that facilitate or accelerate reactions.) Since the 1950s, catalysts have also revolutionised the development of synthetic polymers. By allowing more careful control over polymerization reactions, polymers with new properties, such as the ability to emit coloured light, have been manufactured.