Amino acids, proteins and DNA (A-level only)

This topic explores the chemistry of amino acids, the building blocks of proteins, and the structure of DNA. You will learn how amino acids link via peptide bonds to form polypeptides, which fold into functional proteins. The specific sequence of amino acids determines a protein's shape and function, from enzymes to structural components. Understanding this is crucial for grasping how biological molecules drive life processes.

Proteins are polymers of amino acids, each with a central carbon bonded to an amino group, carboxyl group, hydrogen, and a variable R group. The R group gives each amino acid unique properties (e.g., acidic, basic, polar, non-polar). In aqueous solutions, amino acids exist as zwitterions, which affect their solubility and isoelectric points. You'll also study the four levels of protein structure: primary (sequence), secondary (α-helix, β-pleated sheet), tertiary (3D folding), and quaternary (multiple subunits).

DNA, the molecule of heredity, is a polymer of nucleotides. Each nucleotide contains a phosphate, deoxyribose sugar, and a nitrogenous base (A, T, C, G). The double helix is held together by hydrogen bonds between complementary base pairs (A-T, C-G). This topic also covers how DNA replicates semi-conservatively and how the genetic code is transcribed into mRNA and translated into proteins. These concepts are fundamental to molecular biology and underpin modern biotechnology.