biological molecules

• The primary structure of a protein refers to the linear sequence of amino acids in the polypeptide chain.
• Key molecules required to build structures for organisms to function:

  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic Acids
  • Water
• Polymers are molecules made from a large number of monomers joined together in a chain
• Monomers are smaller units from which larger molecules are made
• Carbohydrates, proteins, lipids, and nucleic acids contain carbon (C) and hydrogen (H) making them organic compounds
• Carbon atoms are key to organic compounds because:

  • Each carbon atom can form four covalent bonds, making the compounds very stable
  • Carbon atoms can form covalent bonds with oxygen, nitrogen, and sulfur
  • Carbon atoms can bond to form straight chains, branched chains, or rings
  • Carbon compounds can form small single subunits (monomers) that bond with many repeating subunits to form large molecules (polymers) through polymerisation
• Macromolecules are very large molecules containing 1000 or more atoms, therefore having a high molecular mass
• Polymers can be macromolecules, but not all macromolecules are polymers as the subunits of polymers have to be the same repeating units
• Three types of carbohydrates:

  • Monosaccharides
  • Disaccharides
  • Polysaccharides
• A covalent bond is the sharing of two or more electrons between two atoms
• Covalent bonds can be nonpolar (equal sharing) or polar (unequal sharing)
• Covalent bonds are very stable and require high energies to break
• Multiple pairs of electrons can form double bonds (e.g. unsaturated fats C=C) or triple bonds
• Condensation (dehydration synthesis) reaction:

  • Monomers combine by covalent bonds to form polymers or macromolecules, and water is removed
• Hydrolysis:

  • Involves breaking covalent bonds in polymers when water is added
• Reducing sugars can donate electrons, making them the reducing agent
• Reducing sugars can be detected using Benedict’s test as they reduce soluble copper sulphate to insoluble brick-red copper oxide
• Examples of reducing sugars include: glucose, fructose, and galactose
• Fructose and galactose have the same molecular formula as glucose but a different structural formula
• Non-reducing sugars cannot donate electrons and therefore cannot be oxidised
• Non-reducing sugars must be hydrolysed into monosaccharides before a Benedict’s test can be carried out
• Example of a non-reducing sugar: sucrose
• Glucose is the most common monosaccharide with the molecular formula C6H12O6
• Glucose exists in two structurally different forms: alpha (α) glucose and beta (β) glucose, known as isomers
• Different types of monosaccharides are formed from molecules with varying numbers of carbon atoms, such as trioses (3C), pentoses (5C), and hexoses (6C)
• Monosaccharides are bonded together to form disaccharides and polysaccharides for transport, storage, and to have less influence on a cell’s osmolarity
• Disaccharides and polysaccharides are formed when two hydroxyl (-OH) groups interact to form a glycosidic bond
• Each glycosidic bond results in the removal of one water molecule through condensation
• Different types of glycosidic bonds form depending on the interacting OH groups, catalysed by specific enzymes (e.g., maltose has an α-1,4 glycosidic bond, and sucrose has an α-1,2 glycosidic bond)
• The glycosidic bond is broken when water is added in a hydrolysis reaction
• Disaccharides and polysaccharides are broken down in hydrolysis reactions
• Hydrolytic reactions are catalyzed by enzymes, different from those present in condensation reactions
• Examples of hydrolytic reactions include:

  • Digestion of food in the alimentary tract
  • Breakdown of stored carbohydrates in muscle and liver cells for use in cellular respiration
• Sucrose is a non-reducing sugar that gives a negative result in a Benedict’s test
• When sucrose is heated with hydrochloric acid, it provides the water that hydrolyses the glycosidic bond, resulting in two monosaccharides that will produce a positive Benedict's test