lesson 5 lipids
Post on 16-Apr-2017
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LipidsLearning objectives…
• Show the formation of a triglyceride•Compare the structure of phospholipids and triglycerides
• Relate structure to function
Glycerol and Fatty Acids• Found in all storage fats and oils, including membranes• The glycerol molecule is always the same, but the fatty
acid differs• Most fatty acids can be made, except for ones called
essential fatty acids which must be eaten
Fatty Acids• All fatty acids have an acid group (part) at one
end, the rest of the molecule is a hydrocarbon chain (a chain made of carbons and hydrogens)
• The hydrocarbon chain can be 2 to 20 carbons long, but most have around 18
Acid Group Hydrocarbon chain
Phospholipids• Almost the same as a triglyceride, but the third fatty acid is
not added, instead a phosphate joins to the 3rd OH by a condensation reaction
• The phosphate head is hydrophilic, and the fatty acids are hydrophobic.
• As the majority of the molecule is insoluble, but the phosphate head is hydrophilic it is able to form membranes
Phospholipids in membranes• Phospholipids may still be
saturated or unsaturated.• Organisms can control the
fluidity of their membranes using this feature
• Organisms living in colder climates have more unsaturated fatty acids in their phospholipid molecules ensuring their membranes remain fluid in low temperatures
(p) compare, with the aid of diagrams, the structure of a triglyceride and a phospholipid;
TriglycerideGlycerol plus three fatty acidsjoined by 3 ester bonds between the fatty acids and
the glycerolIn plants the fatty acids are unsaturated (many double
bonds) and the triglycerides are oilsIn animals the fatty acids are saturated (few or no
double bonds) and the triglycerides are more solidPhospholipidGlycerol plus two fatty acids and a phosphate group
joined by 2 ester bonds
(q) explain how the structures of triglyceride and phospholipid molecules relate to their functions
in living organisms;Triglyceride• Compact energy store, low mass to energy ratio (means mammals have to carry
less mass)• Insoluble in water (large non-polar molecules)• Does not affect cell water potential• Stored as fat providing insulation and protection• Provides buoyancy• Provides waterproofing (on feathers, leaves)• Source of water (from respiration – camel’s humps) • Provides electrical insulation around neurones • Helps in the absorption of fat soluble / A / D / E / K, vitaminsPhospholipid• Part hydrophilic (head), part hydrophobic (tail), so ideal basis for cell surface
membranes• Phosphate may have carbohydrate attached forming glycolipids involved in cell
signalling
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