Topic 2: Biological Molecules Flashcards
In a food lab, describe the test and result for:
(a) Reducing sugars [1 Mark]
(b) Starch [1 Mark]
(c) Lipids [1 Mark]
(d) Proteins [1 Mark]
(a) Benedict’s, heat, brick-red ppt. (1 mark)
(b) Iodine, blue-black. (1 mark)
(c) Ethanol, water, white emulsion. (1 mark)
(d) Biuret, lilac. (1 mark)
In a juice sample, outline how to test for:
(a) Non-reducing sugars [1 Mark]
(b) Semi-quantitative Benedict’s for glucose [1 Mark]
(a) Hydrolyse with HCl, neutralise with NaHCO₃, Benedict’s, red ppt. (1 mark)
(b) Heat with Benedict’s, time colour change, compare standard. (1 mark)
Definitions II:
(a) Monosaccharide
(b) Disaccharide
(c) Polysaccharide
Definitions II:
(a) Monosaccharide: Single sugar unit, e.g., glucose.
(b) Disaccharide: Two monosaccharides joined by a glycosidic bond, e.g., sucrose.
(c) Polysaccharide: Many monosaccharides linked together, e.g., starch.
Definitions I:
(a) Monomer
(b) Polymer
(c) Macromolecule
Definitions I:
(a) Monomer: Small molecule that can join to form a polymer.
(b) Polymer: Large molecule made of repeating monomers.
(c) Macromolecule: Very large molecule, e.g., proteins or DNA.
Definitions III:
(a) Covalent bond
(b) Glycosidic bond
(c) Ester bond
Definitions III:
(a) Covalent bond: Bond formed when atoms share electrons.
(b) Glycosidic bond: Bond between two monosaccharides.
(c) Ester bond: Bond between hydroxyl group and carboxyl group, found in lipids.
Draw the structures of:
(a) α-glucose [1 Mark]
(b) β-glucose [1 Mark]
(c) Sucrose [1 Mark]
(a) α-glucose: 6-C ring, -OH below C1. (1 mark)
(b) β-glucose: 6-C ring, -OH above C1. (1 mark)
(c) Sucrose: Glucose + fructose, 1-2 bond. (1 mark)
Explain glycosidic bond formation and breakage in maltose from digestion. [2 Marks]
Formation: Glucose + glucose, 1-4 bond, H₂O out (1 mark); Hydrolysis: H₂O breaks bond, monosaccharides (1 mark). (2 marks)
Describe the molecular structure and function of cellulose in plant stems. [2 Marks]
β-glucose, 1-4 links, H-bonded fibres (1 mark); Rigid support for plant stems (1 mark). (2 marks)
Compare the structure of amylose and amylopectin in a potato tuber. [3 Marks]
Amylose: α-1,4, helical, compact (1 mark); Amylopectin: α-1,4 and 1-6, branched (1 mark); Energy storage in tuber (1 mark). (3 marks)
Outline the structure and role of triglycerides in human fat cells. [2 Marks]
Glycerol + 3 fatty acids, ester bonds (1 mark); Energy storage in fat cells (1 mark). (2 marks)
Describe the structure of phospholipids in a nerve cell membrane. [3 Marks]
Polar head, non-polar tails, bilayer (1 mark); Fluid barrier in nerve cells (1 mark); Selective transport (1 mark). (3 marks)
In tendon tissue, describe collagen’s structure and its fibrous role. [4 Marks]
Triple helix, Gly-X-Y sequence (1 mark); Cross-linked fibres (1 mark); Fibrous, tensile strength (1 mark); Supports tendons (1 mark). (4 marks)
Explain how haemoglobin’s structure aids oxygen transport in blood. [4 Marks]
4 subunits, haem groups, iron binds O₂ (1 mark); Globular, soluble (1 mark); Cooperative binding (1 mark); Efficient transport in blood (1 mark). (4 marks)
Define the protein structure levels:
(a) Primary [1 Mark]
(b) Secondary [1 Mark]
(c) Tertiary [1 Mark]
(d) Quaternary [1 Mark]
(a) Primary: Amino acid sequence, peptide bonds (1 mark)
(b) Secondary: α-helix/β-sheet, H-bonds (1 mark)
(c) Tertiary: 3D fold, multiple bonds (1 mark)
(d) Quaternary: Subunit assembly, e.g., haemoglobin (1 mark)
Explain two water properties and their roles in a fish’s aquatic environment. [2 Marks]
Solvent: Dissolves nutrients for fish (1 mark); Heat capacity: Stabilises pond temperature (1 mark). (2 marks)
Compare glycosidic bond formation in glycogen with ester bonds in lipids. [3 Marks]
Glycosidic: Sugars, 1-4/1-6, H₂O out (1 mark); Ester: Glycerol + fatty acids, H₂O out (1 mark); Glycogen stores energy, lipids insulate (1 mark). (3 marks)
