Biomolecules
Biomolecules tests carbohydrates, proteins, enzymes, vitamins and nucleic acids. Expect structure-function links and simple classification.
Carbohydrates and proteins
Monosaccharides cannot be hydrolysed; glucose is an aldohexose and fructose a ketohexose. Sucrose is a non-reducing disaccharide because its glycosidic bond links the anomeric carbons of glucose and fructose. Starch is a storage polysaccharide; cellulose is structural. Amino acids exist as zwitterions near neutral pH and join by peptide bonds. Denaturation destroys secondary and tertiary structure without breaking peptide bonds.
Nucleic acids and vitamins
DNA contains deoxyribose and thymine; RNA contains ribose and uracil. DNA is a double helix with A-T and G-C base pairs; RNA is usually single-stranded. Vitamins A, D, E and K are fat-soluble; B and C are water-soluble.
Worked example
Sucrose does not reduce Tollens' reagent or Fehling's solution. Hydrolysis with dilute acid gives glucose and fructose, and the resulting mixture does reduce the reagents. The reasoning is that the glycosidic bond ties up both anomeric carbons, so no free aldehyde or ketone is available until hydrolysis.
Traps
Assuming all carbohydrates are reducing sugars, confusing DNA and RNA bases, and saying denaturation hydrolyses peptide bonds are common mistakes.