Polymers

Polymers Organic compounds are capable of reaching monumental sizes. Proteins and nucleic acids have thousands of atoms. These molecules are composed of simple, repeating units. A polymer is a large molecule composed of covalently bonded smaller molecules.

(n)Monomers  Polymer The repeating units of a polymer are called monomers. We can write the process symbolically:   n monomer  (monomer)n Amino acids and nucleotides are examples of monomers, proteins, DNA and RNA are examples of polymers The biotechnology industry is based on the controlled hydrolysis of monomers from nucleic acid polymers (DNA and RNA) Glycogen and starch are examples of polysaccharides, long chain polymers of sugar monomers. The plastics industry is responsible for many other synthetic polymers.

Making Polymers There are two basic ways to create a polymer from monomers: addition polymerization – unsaturated hydrocarbons react with each other to form polymers condensation polymerization – water is removed from two monomers (dehydration synthesis)

Addition Polymerization: Polyethylene In addition polymerization, the double bond in CH2=CH2 can be broken, forming a ethylene monomer with two unpaired electrons: •CH2 – CH2• When several units of ethylene monomers combine, the result is  •CH2 – CH2• + •CH2 – CH2•  •CH2 – CH2 - CH2 -CH2•

Polyethylene Polymers This process can continue for a long time, creating very large molecules – polyethylene (polyethene) polymers. 

Other Important Industrial Polymers Nylon PVC (polyvinyl chloride)

Sodium Polyacrylate Kevlar Teflon

Condensation Polymerization In condensation polymerization, polysaccharide production offers a prime example. The production of sucrose, a disaccharide, approaches 10 billion metric tons yearly.

More on Polysaccharides Of course, humans do not actually perform the synthesis of sucrose. Plants like sugar cane contain enzymes called synthases that do the job for us. These dimers are often the first step in the production of longer chained polysaccharides such as cellulose and starch:

Other Biopolymers Nucleic acids (DNA and RNA) are composed of nucleotide monomers. Nucleotides have three components: an unsaturated, mono- or bicyclic “base,” a sugar (deoxyribose in DNA, ribose in RNA) a phosphate group

Biopolymers: Proteins The generalized structure for an amino acid is The differences in the R groups account for the different properties that amino acids can have. Of the 20 amino acids found in our bodies, there are polar and non-polar, acidic and basic, and aromatic and aliphatic varieties. The diversity of the R groups allow for flexibility in protein structure and function.

The Chemistry of Ribosomes Proteins are produced from amino acids via condensation – a molecule of water is removed and the carboxyl group of one amino acid is bonded to the amino group of another amino acid:

Peptide Bonds The amino acids are joined to form peptides. The peptide “joint” is called an amide group. The connection between the amino group and the carbonyl group is also called a peptide bond:

Lipids Lipids are also considered polymers. They are composed of three esters of fatty acids bonded to a glycerol molecule: Note that the R groups in this case are saturated and/or unsaturated hydrocarbons with between 14 and 20 carbons.

Saponification This reaction is easily reversed by adding base. NaOH hydrolyses triglycerides into glycerol and the corresponding fatty acids: