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DNA polymer formed from nucleic acid monomers. Protein polymer formed from amino acid monomers.

Image credit: U.S. Department of Energy Genome Programs


Polymers are large molecules composed of many similar smaller molecules linked together. The individual smaller molecules are called monomers. When small organic molecules are joined together, giant molecules are produced. These giant molecules are known as macromolecules.

Generally speaking, all macromolecules are produced from a small set of about 50 monomers. Different macromolecules vary because of the arrangement of these monomers. By varying the sequence, an incredibly large variety of macromolecules can be produced. While polymers are responsible for the molecular "uniqueness" of an organism, the common monomers mentioned above are nearly universal.

The variation in the form of macromolecules is largely responsible for molecular diversity. Much of the variation that occurs both within an organism and among organisms can ultimately be traced to differences in macromolecules. Macromolecules can vary from cell to cell in the same organism, as well as from one species to the next.

Polymers: Biological Macromolecules

There are four basic kinds of biological macromolecules. They are carbohydrates, lipids, proteins and nucleic acids. These polymers are composed of different monomers and serve different functions.
  • Carbohydrates - composed of sugar monomers and necessary for energy storage.

  • Lipids - include fats, phospholipids and steroids. Lipids help to store energy, cushion and protect organs, insulate the body and form cell membranes.

  • Proteins - composed of amino acid monomers and have a wide variety of functions including molecular transport and muscle movement.

  • Nucleic Acids - include DNA and RNA. Nucleic acids contain instructions for protein synthesis and allow organisms to transfer genetic information from one generation to the next.

Assembling and Disassembling Polymers

While there is variation among the types of polymers found in different organisms, the chemical mechanisms for assembling and disassembling them are largely the same across organisms. Monomers are generally linked together through a process called dehydration synthesis, while polymers are disassembled through a process called hydrolysis. Both of these chemical reactions involve water. In dehydration synthesis, bonds are formed linking monomers together while losing water molecules. In hydrolysis, water interacts with a polymer causing bonds that link monomers to each other to be broken.
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