biological molecules

• Benedict’s solution can be used to test for reducing sugars like glucose, fructose, and maltose, changing color from blue to brick red in their presence
• If there is no color change with Benedict’s solution, it could indicate the presence of a non-reducing sugar like sucrose, which can be confirmed by breaking glycosidic bonds through acid hydrolysis
• Steps for semi-quantitative Benedict’s test:

  1. Add dilute HCl to the test solution and heat in a water bath

  2. Neutralize with sodium hydrogencarbonate

  3. Heat with Benedict’s solution

  • Time for color change can estimate concentration
  • Color changes can be used for colorimetry to determine glucose concentration
• Chemical test for starch uses iodine/potassium iodide, turning blue/black if starch is present
• Emulsion test for lipids involves adding ethanol to the test substance, shaking, then mixing with water to observe a milky color for a positive lipid result
• Biuret test for proteins:

  • Add sodium hydroxide solution and copper (II) sulphate solution
  • Color change from blue to purple indicates the presence of proteins
• Carbohydrates consist of monosaccharides, disaccharides, and polysaccharides formed by glycosidic bonds in condensation reactions
• Monosaccharides:

  • Glyceraldehyde is a triose
  • Ribose is a pentose sugar
  • Glucose is a main substrate for respiration with alpha and beta isomers
• Disaccharides:

  • Maltose: two glucose molecules
  • Sucrose: glucose & fructose
  • Lactose: glucose & galactose
• Polysaccharides:

  • Glycogen and starch from alpha glucose
  • Cellulose from beta glucose
• Glycogen:

  • Main energy storage in animals
  • Formed from alpha glucose with 1, 4 and 1, 6 glycosidic bonds
  • Many side branches for quick energy release
• Starch:

  • Mixture of amylose and amylopectin
  • Amylose: unbranched chain of glucose molecules
  • Amylopectin: branched chain for rapid digestion
• Cellulose:

  • Component of plant cell walls
  • Composed of long, unbranched chains of beta glucose joined by glycosidic bonds
  • Provides structural support in plant cells
• Lipids are only soluble in organic solvents like alcohols and include saturated lipids found in animal fats and unsaturated lipids found in plants
• Saturated lipids don't contain any carbon-carbon double bonds and can increase cholesterol levels in blood, raising the risk of coronary heart disease
• Unsaturated lipids found in plants contain carbon-carbon double bonds and melt at lower temperatures than saturated fats, providing essential fatty acids
• Triglycerides are non-polar, hydrophobic molecules composed of glycerol and three fatty acids joined by ester bonds formed in condensation reactions
• Triglycerides serve as energy reserves in plant and animal cells
• Phospholipids have a phosphate-containing group substituting one fatty acid of a triglyceride, with hydrophilic phosphate heads and hydrophobic tails, forming micelles in water
• Proteins are made of amino acids joined by peptide bonds in condensation reactions
• The primary structure of a protein is the order and number of amino acids, while the secondary structure can be alpha helix or beta pleated sheet, determined by hydrogen bonding, ionic bonds, and disulphide bridges
• The tertiary structure of proteins is the 3D shape, either globular (soluble) or fibrous (insoluble), like collagen in bones and keratin in fibers
• Quaternary structure of proteins consists of 2 or more subunits closely packed together, like haemoglobin carrying oxygen in the blood
• Peptide bonds in proteins can be hydrolyzed with the addition of water in a hydrolysis reaction
• Water is a polar molecule, a metabolite in metabolic reactions, a solvent, has a high specific heat capacity, a relatively large latent heat of vaporization, strong cohesion between molecules, and high surface tension at the water-air boundary