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2.2.12 · Biological Molecules

Biological Molecules- Key Terms — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 8 parts Lesson 7 of 25 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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2.2.1 Biological Molecules: Key Terms — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Define monomers, polymers and macromolecules, and describe carbohydrate classes and the isomers of glucose.Main groups — carbohydrates, proteins, lipids, nucleic acids and water.Or…

  • Organic compounds
  • Four bonds
  • Other atoms
  • Monosaccharide sizes
  • General formula
  • Polymerisation

Section 1 of 8Key biological molecules

Key biological molecules
Main groups
  • Main groups carbohydrates, proteins, lipids, nucleic acids and water.
Organic compounds
  • Organic compounds carbohydrates, proteins, lipids and nucleic acids all contain carbon and hydrogen.

Section 2 of 8Why carbon is central

Four bonds
  • Four bonds each carbon forms four strong covalent bonds, making compounds very stable.
Other atoms
  • Other atoms carbon bonds with oxygen, nitrogen and sulfur.
Shapes
  • Shapes carbon forms straight chains, branched chains and rings.

Section 3 of 8Monomers, polymers and macromolecules

Monomer
  • Monomer a small single subunit.
Polymer
  • Polymer many repeating monomers bonded together by polymerisation.
Macromolecule
  • Macromolecule a molecule of 1000 or more atoms with a high molecular mass.
  • Not all macromolecules are polymers, because polymer subunits must be repeating units.
Examples
  • Examples the monomer of nucleic acids is a nucleotide.

Section 4 of 8Glucose and its isomers

Formula
  • Formula glucose is C6H12O6 and is the most common monosaccharide.
Monosaccharide sizes
  • Monosaccharide sizes trioses, pentoses (5C, ribose) and hexoses (6C, glucose).
    • (3C, glyceraldehyde)
Isomers
  • Isomers alpha-glucose and beta-glucose have the same formula but different structures.
PolysaccharideAlpha-glucoseBeta-glucose
StarchYesNo
GlycogenYesNo
CelluloseNoYes

Section 5 of 8Types of carbohydrate

TypeDefinitionExamplesFunctions
MonosaccharideA single sugar, all reducingGlyceraldehyde, ribose, glucoseRespiration, building blocks
DisaccharideTwo monosaccharides joined by a glycosidic bondMaltose, sucrose, lactoseSeed sugar, milk sugar, transport sugar
PolysaccharideMany monosaccharides joined by glycosidic bondsStarch, glycogen, celluloseEnergy storage, cell walls
  • General formula
    • Cx(H2O)y, with H and O in the ratio 2:1.

Section 6 of 8More from the specification

Triglyceride Synthesis
  • Formed through condensation reactions between one glycerol molecule and three fatty acid chains, releasing three water molecules and creating three covalent ester bonds.
Phospholipid Bilayer Architecture
  • Phospholipids contain a hydrophilic phosphate head and two hydrophobic fatty acid tails, naturally forming the structural foundation of cell membranes.
Condensation and Hydrolysis Reactions
  • Biological macromolecules are assembled from simpler reducing sugars and monomers via condensation reactions involving shared electron pairs,
  • and degraded by hydrolysis.
Hydrophobic Interactions in Lipids
  • Non-polar hydrocarbon fatty acid tails aggregate away from surrounding water molecules, establishing an effective hydrophobic barrier across the membrane.
Triglyceride
  • A lipid made of glycerol and three fatty acids.
Phospholipid
  • Glycerol, two fatty acids and a phosphate group, which is amphipathic.
Hydrophobic
  • Water-hating; non-polar and unable to dissolve in water.
Condensation
  • A reaction that joins molecules and removes water.
Fatty acid
  • A hydrocarbon chain with a carboxyl group.
Non-reducing sugar
  • A sugar that cannot reduce Benedict's reagent until hydrolysed.
Condensation reaction
  • A reaction that joins two molecules by a covalent bond and releases water.

Section 7 of 8Key terms

TermMeaning
MonomerA small subunit that bonds with others to form a polymer.
PolymerA large molecule made of many repeating subunits.
MacromoleculeA very large molecule with 1000 or more atoms.
PolymerisationJoining monomers to form a polymer.
IsomerA molecule with the same formula but a different structure.
DisaccharideA sugar made of two monosaccharides.
PolysaccharideA polymer of many monosaccharides.

Section 8 of 8Exam technique

1
Saying every macromolecule is a polymer — lipids are macromolecules but not polymers.
2
Mixing up alpha and beta glucose polymers — alpha gives starch and glycogen, beta gives cellulose.
3
Saying monosaccharides are non-reducing — all monosaccharides are reducing sugars.
4
Naming monomers vaguely — give specific examples, e.g. nucleotide for nucleic acids.

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