Biological Polymers - Biomolecules

Sugar Polymer
Disaccharide molecular model of sugar as glucose and fructose. Sugar or sucrose is a biological polymer composed of glucose and fructose monomers. David Freund/Stockbyte/Getty Images

Biological polymers are large molecules composed of many similar smaller molecules linked together in a chain-like fashion. The individual smaller molecules are called monomers. When small organic molecules are joined together, they can form giant molecules or polymers. These giant molecules are also called macromolecules. Natural polymers are used to build tissue and other components in living organisms.

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. 

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Biomolecules

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 - molecules composed of sugar monomers. They are necessary for energy storage. Carbohydrates are also called saccharides and their monomers are called monosaccharides. Glucose is an important monosaccharide that is broken down during cellular respiration to be used as an energy source. Starch is an example of a polysaccharide (many saccharides linked together) and is a form of stored glucose in plants.
  • Lipids - water insoluble molecules that can be classified as fatsphospholipids, waxes, and steroids. Fatty acids are lipid monomers that consist of a hydrocarbon chain with a carboxyl group attached at the end. Fatty acids form complex polymers such as triglycerides, phospholipids, and waxes. Steroids are not considered true lipid polymers because their molecules do not form a fatty acid chain. Instead, steroids are composed of four fused carbon ring-like structures. Lipids help to store energy, cushion and protect organs, insulate the body, and form cell membranes.
  • Proteins - biomolecules capable of forming complex structures. Proteins are composed of amino acid monomers and have a wide variety of functions including transportation of molecules and muscle movement. Collagen, hemoglobin, antibodies, and enzymes are examples of proteins.
  • Nucleic Acids - molecules consisting of nucleotide monomers linked together to form polynucleotide chains. DNA and RNA are examples of nucleic acids. These molecules contain instructions for protein synthesis and allow organisms to transfer genetic information from one generation to the next.

 

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Assembling and Disassembling Polymers

While there is variation among the types of biological 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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Synthetic Polymers

Unlike natural polymers, which are found in nature, synthetic polymers are man-made. They are derived from petroleum oil and include products such as nylon, synthetic rubbers, polyester, Teflon, polyethylene, and epoxy. Synthetic polymers have a number of uses and are widely used in household products. These products include bottles, pipes, plastic containers, insulated wires, clothing, toys, and non-stick pans.