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LIPIDS (complex lipids: PHOSPHOLIPIDS (STRUCTURE (made of 1 glycerol…
LIPIDS
complex lipids: PHOSPHOLIPIDS
STRUCTURE
made of 1 glycerol bonded to 2 fatty acid molecules (joined by ester linkages) and 1 phosphate group (joined by phosphoester bond)
fatty acid and glycerol is insoluble in water (hydrophobic)
phosphate is negatively charged : hydrophilic
phosphate group can have small molecules attached to it
structure - function: hydrophilic head (phosphate) and hydrophobic hydrocarbon tail (glycerol, fatty acid) causes it to be
amphipathic
FUNCTION
major component of cell surface membrane and membrane of organelles
spontaneously forms a bilayer: hydrophilic heads face water, hydrophobic tails forms the core of cell membrane (ref. cell membrane)
allows for compartmentalisation (separation between external and internal cell environments)
simple lipids: TRIGLYCERIDES
STRUCTURE: made of glycerol and fatty acids
glycerol: by itself, soluble in water due to the presence of OH groups
fatty acids: contains a hydrocarbon chain (insoluble) a carboxylic acid group. One end is soluble, the other is not
Saturated: Each carbon has 4 hydrogens attached
unsaturated: has C=C double bond
creates a 'kink' in the hydrocarbon tail, preventing molecules from packing closely together
weakest intermolecular attractions and lowers melting point
greater number of kinks, lower melting point
greater length of hydrocarbon chain, more extensive hydrophobic interactions (IMF), greater melting point
Fatty acids join to glycerol through condensation reaction, forming
ester linkages
lipid is now insoluble in water as OH groups are removed
1 glycerol combines with 3 fatty cads (3 ester linkages)
OH group in glycerol reacts with -COOH group of fatty acid, removing one water molecule
ester linkage (-COO-) formed
lipid is now insoluble in water as OH groups are removed
FUNCTION
storage form of energy
insoluble in water (large and uncharged)
Doesn't affect water potential of cells (won't diffuse out of cells & can be stored)
more C-H bonds
provides more energy per unit mass
good long term energy store
source of metabolic water (water produced from oxidising food)
more hydrogen, which yields water on oxidation
good thermal insulator
buoyancy to aquatic mammals
fat is less dense than water
protective layer for internal organs
steroids & sterols
carbon skeleton containing 4 fused rings
steroid nucleus with OH (hydroxyl group) = sterol