Macromolecules

Introduction to Macromolecules and Polymerization

Macromolecules are large, complex molecules formed by the joining of thousands of smaller units called monomers. The primary chemical process by which these monomers link together is polymerization. In board exams, you must be able to distinguish between the two major types of polymerization: addition polymerization, which occurs when unsaturated monomers (usually containing double bonds like ethene) add to each other without losing any atoms or molecules, and condensation polymerization, which involves the stepwise joining of monomers with the simultaneous elimination of small molecules such as water ($H_2O$) or hydrogen chloride ($HCl$). Understanding the repeating structural units of polymers like polyethene, PVC, and polyesters is a frequent requirement in short-answer questions.

Carbohydrates and Proteins

Carbohydrates are polyhydroxy aldehydes or ketones, or substances that yield them upon hydrolysis. They are classified into monosaccharides (simple sugars like glucose and fructose), oligosaccharides (containing 2-10 monosaccharide units, such as sucrose), and polysaccharides (complex carbohydrates like starch, glycogen, and cellulose). Pay special attention to the glycosidic linkage that holds sugar units together. Proteins are high-molecular-weight polymers of $\alpha$-amino acids linked together by peptide bonds. In your exams, expect questions asking about the structural levels of proteins—primary, secondary ($\alpha$-helix and $\beta$-pleated sheet), tertiary, and quaternary structures—as well as the process of denaturation, which disrupts these structures through heat, pH changes, or heavy metals.

Lipids and Nucleic Acids

Lipids are a heterogeneous group of organic compounds related to fatty acids that are insoluble in water but soluble in non-polar organic solvents. This class includes true fats and oils (esters of glycerol and fatty acids, known as triglycerides), phospholipids (crucial components of cell membranes), and steroids (such as cholesterol). Board exams frequently test your knowledge on the difference between saturated and unsaturated fatty acids, the concept of saponification (alkaline hydrolysis of fats to make soap), and the iodine value as a measure of unsaturation. Finally, nucleic acids—DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)—are polynucleotides responsible for the storage and transfer of genetic information. You should memorize the basic nucleotide structure (pentose sugar, nitrogenous base, and phosphate group) and the specific base-pairing rules (Adenine pairs with Thymine/Uracil, Cytosine pairs with Guanine) governed by hydrogen bonding.