Biological reactions
If you take IB Biology, you will learn about metabolism. This is the complex network of interdependent and interacting chemical reactions occurring in living organisms. This typically involves the interchange between basic unit molecules, called monomers, and large polymers, called macromolecules.
To form these, chemical reactions involved in metabolism are divided into two types:
- Catabolic reactions – these are reactions that break down macromolecules into monomers. All biological monomers will be formed via a hydrolysis reaction, which uses water to split the macromolecule.
- Anabolic reactions – these are reactions that combine monomers to form macromolecules. All biological macromolecules are formed via a condensation reaction, which produces water or methanol from the monomers.
In this topic, you are expected to focus on the formation of polymers via condensation reactions.
Condensation polymerization
Since the nature of condensation reactions is to release water or methanol, it means that the monomers involved must have functional groups with oxygen and hydrogen - such as a hydroxyl, amine, or carboxylic acid group. In order to form a polymers, these groups must be present on both sides of the molecule so that the monomer can lengthen in both directions.
However, we know that polymers typically have a repeating structure. You are expected to remember two examples: polyesters and polyamides.
Polyesters are formed when a dialcohol reacts with a dicarboxylic acid, forming a water molecule for every ester link.
A common commercial polyester is polyethylene terphthalate (PET), formed from the condensation reaction between ethylene glycol and terephthalic acid. This is often threaded to be used in clothes or used as a hard plastic in water bottles.
Polyamides are formed when a diamine reacts with a dicarboxylic acid, forming a water molecule for every amide link.
This creates the common commercial polyamide called Nylon 66. This is spun into fibers for textiles, carpets, and molded parts.
Polyamides can also be formed when an amino-carboxylic acid (amino acid) reacts with itself, also forming a water molecule for every amide link.
This is performed in organisms to synthesize protein chains that then combine with other chains or fold into the final functional protein.