2 Lipids (DIY)

• Glycerol (STRUCTURE)

  • Polar molecule
  • 3-carbon alcohol, each carbon bearing a polar hydroxyl group
• Glycerol (PROPERTIES)

  • Soluble in water (polar hydroxyl groups allowing it to form hydrogen bonds with water molecules)
  • Hydrophilic and viscous (able to form hydrogen bonds)
  • Higher density than water
• Fatty Acids (STRUCTURE)

  • Non-polar molecule
  • Long-chained carboxylic acids containing an even number of carbon atoms (usually 14-22)
  • Consists of a long non-polar  hydrogen chain + functional group (carbonyl group -COOH)
• Fatty Acids (PROPERTIES)

  • Insoluble in water (non-polar C-H bonds does not allow it to form hydrogen bonds with water molecules)
  • Hydrophobic (unable to form hydrogen bonds)
  • Soluble in organic solvents
• Fatty Acids (TYPES - Saturated)

  • SATURATED: NO C=C double bonds in the hydrocarbon tail
  • When number of C-atoms in a fatty acids increases, the higher its melting point
  • Increased hydrophobic interactions between hydrocarbon tails of the fatty acid, causes more energy to be required to weaken and break hydrophobic interactions between hydrocarbon chains
• Fatty Acids (TYPES - Unsaturated)

  • UNSATURATED: possesses one or more C=C double bonds in the hydrocarbon tail
  • C=C double bond creates a ‘kink’ (rigid bend) in the hydrocarbon tail —> reduces hydrophobic interactions. There is no close packing to one another
  • When number of kinks increases, the close packing of fatty acids molecules are prevented more, distance between fatty acid molecules increases
  • Decreased hydrophobic interactions between hydrocarbon tails of the fatty acid, causing less energy being required to weaken and break hydrophobic interactions between the hydrocarbon chains
• Ester Bond

  • FORMATION:
  • Each hydroxyl group (-OH) reacts with the carbonyl group (-COOH) of a fatty acid and through a condensation reaction each
  • one water molecule is removed to form an ester bond
  • BREAKAGE:
  • An ester bond breaks via a hydrolysis reaction each, with the gaining of one water molecule per reaction
• Triglycerides (STRUCTURE)

  • 3 fatty acids and 1 glycerol molecule joined via ester bonds
  • Releases 3 water molecules per triglyceride formed
• Triglycerides (PROPERTIES - 1)

  • Large + Non-polar hydrocarbon chains (fatty acids)
  • Insoluble in water (hydrophobic hydrocarbon chains unable to form hydrogen bonds with water)
  • Does not affect water potential of storage cells (will not interfere with cellular processes of cell)
• Triglycerides (PROPERTIES - 2)

  • 3 hydrocarbon chains per triglyceride
  • Compact energy storage molecule (each long hydrocarbon chain upon oxidation would release x2 ATP of the same mass of carbohydrates)
• Triglycerides (PROPERTIES - 3)

  • Ester bond between each hydrocarbon chain and glycerol backbone
  • Easily hydrolysed in lipases to release fatty acids from the glycerol backbone (during lipid metabolism to produce ATP molecules from the oxidation of fatty acids)
  • Acts as a long-term energy store in cells
• Triglycerides (FUNCTIONS - 1)

  • Storage energy molecule (main function)
  • Energy is stored in large amounts without affecting the water potential of cells, not able to diffuse out of cells
  • High proportion of C-H bonds releases more ATP upon oxidation
  • Allows mobile animals to carry compact energy stores in their adipose cells for use
• Triglycerides (FUNCTIONS - 2)

  • Source of metabolic water
  • Metabolic water: yielded from the hydrogen part of the triglyceride only (important to desert animals)
  • Better source of metabolic water than carbohydrates due to the number of hydrogen atoms they possess (twice the amount)
• Triglycerides (FUNCTIONS - 3-5)

  • Good thermal insulator
  • Prevents excessive heat loss
  • Protection against mechanical damage
  • Cushions against mechanical damage as a protective layer for delicate internal organs 
  • Provides buoyancy
  • Lipids are less dense than water (important for aquatic mammals)
• Phospholipids (STRUCTURE)

  • Consists of a lipid and a non-lipid component
  • 1 phosphoric acid + 2 fatty acids combined with 1 glycerol
  • Fatty acids are joined via an ester bond
  • Phosphoric acid is joined via a phosphorites bond
• Phospholipids (PROPERTIES)

  • Consists of 1 charged phosphate head + 2 non-polar hydrocarbon chains
  • Amphipathic in nature
  • Arranges itself through self-assembly to form a bilateral structure (charged outwards, non-polar inside to form hydrophobic core)
  • Charged, hydrophilic phosphate head interacts with the aqueous medium
  • Non-polar, hydrophobic hydrocarbon chains of fatty acid interact with each other, away from water, forming a hydrophobic core
  • Hydrophobic core only allows passage of small, non-polar molecules and are partially permeable
• Phospholipids (FUNCTION)

  • Major component of the cell surface membrane and membrane of organelles
  • Separates the cell content from the aqueous external cell environment and compartmentalisation within the cell for specialised biochemical reactions
• Suggest why triglycerides release twice as much energy on oxidation compared with an equivalent mass of carbohydrates

  1. Triglycerides contain proportionally more C-H bonds and lesser oxygen atoms as compared to an equivalent mass of carbohydrates

  • Makes triglycerides more reduced compared to carbohydrates

  1. With a higher proportion of C-H bonds, more oxidation reactions will take place, resulting in more ATP synthesised than that of the oxidation of the carbohydrates

  • Triglycerides are a more compact energy store
•  Suggest why plant cells mainly store carbohydrates and animal cells mainly store lipids

  1. Plants are not mobile while animals are mobile, hence requiring more energy
  2. Lipids are a more compact energy store as oxidation of lipids yield about twice the amount of metabolic energy per unit mass as compared to carbohydrates
  3. For a fixed amount of energy stored, lipids are lighter compared to carbohydrates (better for movement).
  4. Lipids are found beneath the layer of skin - poor conductors of heat --> able to provide thermal insulation to mammals especially those in cooler climates