Chapter 10 โ Biomolecules
The molecules of life: carbohydrates for energy and structure, proteins and enzymes that build and run the cell, vitamins, the nucleic acids that carry heredity, and the hormones that send its messages.
Every chapter so far has studied molecules made in flasks and factories. This one studies the molecules that made you. A slice of chapati is mostly starch, a chain of thousands of glucose units. Your stomach and intestines break that chain down within hours; your cells oxidise the glucose to release energy; and the instructions for building the enzymes that do all this are written in the sequence of four bases in your DNA, copied from your parents and passed on to every new cell. Biomolecules are organic compounds, and they obey the same rules you have learnt for alcohols, carbonyl compounds, amines and acids.
Three big families of polymers do most of the work. Polysaccharides such as starch and cellulose are chains of sugars joined by glycosidic links; proteins are chains of amino acids joined by peptide bonds and folded into precise shapes; nucleic acids are chains of nucleotides joined by phosphodiester links. All three are built by condensation, one water molecule lost for every link, and taken apart by hydrolysis. Alongside them are the small molecules the body needs in tiny amounts: vitamins, which we must eat, and hormones, which our glands make to carry messages through the blood.
| Polymer | Monomer | Link (water lost) | Section |
|---|---|---|---|
| starch, cellulose, glycogen | glucose | glycosidic $\mathrm{C{-}O{-}C}$ | 10.1 |
| proteins | ฮฑ-amino acids | peptide $\mathrm{{-}CO{-}NH{-}}$ | 10.2 |
| DNA, RNA | nucleotides | phosphodiester (3โฒโ5โฒ) | 10.3 |
- classify carbohydrates (mono-, oligo-, polysaccharides; aldoses and ketoses; reducing and non-reducing sugars) and explain the chemical evidence for the open-chain and ring structures of glucose;
- draw Fischer and Haworth projections of glucose and fructose, identify ฮฑ and ฮฒ anomers and D/L configuration, and describe sucrose, maltose, lactose, starch, cellulose and glycogen and their glycosidic links;
- classify amino acids, explain the zwitterion and the isoelectric point, and work out peptide formulas, molar masses and sequence counts;
- describe the primary, secondary, tertiary and quaternary structures of proteins, denaturation, and the action of enzymes as biological catalysts;
- classify vitamins and name their deficiency diseases; describe the composition of nucleic acids, nucleosides and nucleotides, the DNA double helix and base pairing, the types of RNA and their functions, and give an elementary account of hormones.
Sections in this chapter
Carbohydrates
Classification, the open-chain and ring structures of glucose, anomers, fructose, disaccharides and polysaccharides, and why they matter.
Proteins and Enzymes
Amino acids and zwitterions, peptide bonds, the four levels of protein structure, denaturation and enzymes.
Vitamins, Nucleic Acids and Hormones
Fat- and water-soluble vitamins, nucleosides and nucleotides, the DNA double helix and base pairing, RNA, and an introduction to hormones.