Organic Chemistry: Concepts and Applications - Headley Allan D. 2020

Synthetic Polymers and Biopolymers
20.7 Biopolymers

In the previous section, we examined polymers that are made from simple alkenes and other simple molecules to make larger molecules, polymers. In this section, we will examine polymers that are found naturally. These compounds are described as biopolymers and they include peptides, proteins, and carbohydrates. Proteins and peptides are natural polymers, compared to synthetic polymers that were discussed in the previous chapter. Peptides contain repeating units of α-amino acids, and the bond that links the amino acids together is called the peptide bond, or amide bond. Proteins and peptides play very important roles in the structure and function of cells. Carbohydrates are another type of polymer that are found naturally. They are found predominantly in the plant world. They make up more than 50% of the dry weight of the earth's biomass. Chemical energy is stored in the form of carbohydrates. The monomers of carbohydrates have the empirical formula (CH2O)n, where n represents an integer. The formula for glucose, which is one of the repeating units of carbohydrates, is (CH2O)6 or C6H12O6. As a result, carbohydrates are also referred to as hydrates of carbon. A large number of naturally occurring compounds, including cholesterol, fall under a category of compounds called lipids. Lipids are typically not considered to be polymers, but they are fairly large organic molecules that are insoluble in water, but soluble in most organic solvents, such as diethyl ether. Lipids can be divided into three types: (i) triglycerides and waxes; (ii) phospholipids; and (iii) steroids, prostaglandins, and terpenes. Triglycerides, waxes, and phospholipids can be hydrolyzed under acidic or basic conditions to produce smaller molecules, typically carboxylic acids and alcohols. In this chapter, the emphasis will be on a study of the structure, properties, and reactions of the monomers of biopolymers.