Introduction to Biochemistry and Biomolecules
Introduction to Biochemistry and Biomolecules asks you to connect carbon chemistry, water behaviour and functional groups to the molecules of life. The exam tests definitions, polymer formation, pH and buffer calculations, and recognition of the four major biomolecule classes.
Core rules
- Living matter is built mainly from C, H, N, O, P and S; carbon forms four stable covalent bonds and can make chains and rings.
- Micromolecules include glucose, amino acids, fatty acids and nucleotides; macromolecules include polysaccharides, proteins and nucleic acids.
- Polymers form by condensation, which joins monomers and releases water; hydrolysis reverses this.
- Water is polar, forms hydrogen bonds, has high specific heat and is a good solvent for ions and polar molecules.
- pH = −log[H+]; buffers resist pH change when small amounts of acid or base are added.
- Covalent bonds include peptide, glycosidic and phosphodiester links; non-covalent forces include hydrogen bonds, ionic bonds, hydrophobic interactions and van der Waals forces.
Worked example
Find the pH of 0.01 M HCl. HCl is a strong acid, so [H+] = 0.01 = 10−2 M. pH = −log(10−2) = 2. For 0.01 M NaOH, [OH−] = 10−2 M, pOH = 2, and pH = 14 − 2 = 12 at 25 °C. This shows why a tenfold concentration change alters pH by one unit.
Traps that cost marks
Do not call every biomolecule a macromolecule; glucose and ATP are biomolecules but not macromolecules. Do not say a buffer fixes pH-it only resists change. Remember that condensation releases water while hydrolysis consumes it. In pH problems, check whether the question gives [H+] or [OH−].