Polymers are chains of molecular units, or monomers, linked together by covalent bonds. Carbon has the rare ability to form four covalent bonds, so most known polymers are carbon-based. Polymers can be naturally occurring or created in a lab, but both can be useful to humans and polymers like DNA and proteins are vital to life. Polymerization happens when energy is added to a group of monomers, causing them to bond with each other.
Deoxyribonucleic acid, or DNA, is both the blueprint for life and a polymer. The monomer in this case is the nucleotide, made up of a deoxyribose sugar, a phosphate group, and a nitrogen-containing base. There are four different types of nitrogen bases: adenine, cytosine, guanine and thymine. The DNA polymer is created when the sugar group of one nucleotide covalently bonds with the phosphate group of another nucleotide. The order of nucleotides is the genetic code, so the cell carefully oversees the polymerization process, ensuring that the DNA is accurately replicated.
The eel-like hagfish has a singular defense mechanism. Faced with a threat, the fish exudes profuse amounts of slime that clog predators’ gills and make it hard to grab. At the molecular level, the slime is made up of water and ultra-fine protein filaments. Proteins are naturally occurring polymers made up of 20 different nitrogen-containing amino-acid monomers. The polymer-forming peptide bond happens as the carbon from carboxylic acid on one side of an amino acid covalently bonds with the nitrogen from the amine group on another amino acid. The chains of amino acids then fold back on themselves to form a three-dimensional structure, such as slim strands in the case of the hagfish.
Polyethylene is pervasive in our modern lives. It makes up many of the plastics people use every day, such as plastic bags and milk jugs. The monomer for polyethylene is ethylene, a molecule with two carbon atoms joined with a double bond and four hydrogen atoms. The covalent bonds forms when the double bond is broken and reforms between the carbon atoms of individual monomers, leading to a chain of carbon with hydrogen atoms attached. Polyethylene polymers can also attach to each other, forming branched chains.
Polytetrafluoroethylene, or PFTE, is better known by the brand name Teflon. It can be embedded into cookware coating and other products to prevent stains and sticking. The monomer for PFTE is tetrafluoroethylene, or ethylene with fluorine atoms instead of hydrogen atoms. The covalent bonds are between carbon atoms, forming a long chain of carbon atoms with fluorine atoms on the outside. The fluorine is what gives PFTE its repellent properties. Fluorine bonds very strongly inside molecules, but repels other molecules that come close to it. If no molecules can come close, nothing can stick to a surface coated with PFTE.
- The Science of Polymer Molecules; Richard H. Boyd and Paul J. Phillips
- Molecular Biology of the Cell; Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts and Peter Walter
- Biomacromolecules: The Production of Fibers and Films from Solubilized Hagfish Slime Thread Proteins
- Polymer Science Learning Center: Polyethylene
- Polymer Science Learning Center: Polytetrafluoroethylene
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