Proteins
- Amino acids are the monomer units used to make proteins.
- The 20 naturally occurring amino acids only differ in their R groups
- Dipeptides are formed when two amino acids are joined together by a condensation reaction, forming a peptide bond.
- A polypeptide is a polymer made of many amino acids joined together by peptide bonds.
- A protein may contain one or more polypeptide chains.
Level | Definition | Solubility in Water |
Primary | The specific sequence of amino acids in a polypeptide chain | Peptide Bonds |
Secondary | The curling or folding of the polypeptide chain into α-helices and β-pleated sheets due to the formation of hydrogen bonds | Hydrogen Bonds |
Tertiary | The overall specific 3-D shape of a protein, which is determined by interactions between R groups and the properties of R groups | Hydrogen bonds Ionic bonds Disulphide bridges |
Quaternary | The specific 3-D shape of a protein that is determined by the multiple polypeptide chains and/or prosthetic groups bonded together | Hydrogen bonds Ionic bonds Disulphide bridges |
Biochemical tests
Molecule | Reagent | Positive result |
Reducing sugars | Benedict’s reagent → Heat | Red/orange precipitate |
Non-reducing sugars | Hydrochloric acid → Heat Sodium hydrogencarbonate Benedict’s reagent → Heat | Red/orange precipitate |
Starch | Iodine in potassium iodide solution | Blue/black |
Proteins | Sodium hydroxide Copper (II) sulphate | Purple |
Lipids | Ethanol Water → Shake | Cloudy white |