Biological Polymers

A polymer is a particular category of macromolecule that is built by connecting many smaller subunits called monomers (poly- means many). Of the four biological macromolecules that you have been studying, only three are polymers. Lipids are not polymers, but the others are.

• Polysaccharides are macromolecular carbohydrates. Be careful with the words polysaccharide and carbohydrate. They are sometimes used interchangeably but should not be. Carbohydrates include both small molecules and large molecules (macromolecules). Polysaccharides are a type of carbohydrate, but not all carbohydrates are polysaccharides. As the name implies, polysaccharides are polymers made up of multiple monosaccharides. Monosaccharides are monomers, and they can be connected in a linear or branched arrangement.
  
  
• Proteins are polymers that are made up of monomers called amino acids. Unlike polysaccharides, which may be branched, a protein must be a linear (or end-to-end) arrangement of amino acids. Organisms use 20 different kinds of amino acids (in an unlimited number of combinations and orders) to construct their proteins.
  
  
• We can also call a nucleic acid a polynucleotide. That alternative name indicates it is a polymer made up of many nucleotides. In the case of DNA, the monomers are nucleotides containing the pentose (five-carbon sugar) called deoxyribose. For RNA, the nucleotides contain ribose instead of deoxyribose. Although there are only four commonly used DNA nucleotides (and four commonly used RNA nucleotides), a typical DNA molecule contains millions of nucleotides, so there is an unlimited number of sequences of such nucleotides.

Be sure you can match each type of monomer to the type of polymer that can be made from such monomers. You should also know how polymers are constructed using dehydration reactions and deconstructed using hydrolysis reactions.

Watch this lecture to review biological macromolecules and their role in biological organisms. Identify their building blocks and how they form polymers. Also, understand the structures and how they relate to the function of each macromolecule's role in organisms. After watching, you should be able to list the four major classes of macromolecules, distinguish between monomers and polymers, and define the terms dehydration synthesis and hydrolysis.