lipids Flashcards
what are the two groups of lipids?
● triglycerides
● phospholipids
describe the structure of a triglyceride
● one molecule of glycerol
● three fatty acid molecules
what reaction are triglycerides formed by?
condensation
what bond forms between glycerol and a fatty acid in a condensation reaction?
ester bond
what is the basic structure of a fatty acid?
RCOOH
what group is represented by COOH in RCOOH?
carboxyl group
what is R in RCOOH?
variable ‘R’ group hydrocarbon tail
what are the two types of fatty acid R-groups?
● unsaturated
● saturated
describe unsaturated fatty acids (4)
● has C=C double bonds
● ‘kinked’ molecules - fewer contact points
● lower melting point - liquid at room temp
● found in plant oils
describe saturated fatty acids (4)
● has no C=C double bonds - only single bonds
● straight chain molecule - many contact points
● high melting point - solid at room temp
● found in animal fats
what does monounsaturated mean?
1 double bond
what does polyunsaturated mean?
multiple double bonds
how does the structure of triglycerides relate to their functions? (3)
● insoluble hydrocarbon chains - no affect on water potential of cells and used for waterproofing
● high energy : mass ratio - good energy storage molecules
● slow conductor of heat - thermal insulation
describe the structure of phospholipids
● glycerol backbone
● one phosphate head
● two fatty acid tails
what reaction are phospholipids formed by?
condensation
how does the structure of phospholipids relate to their function? (3)
● forms phospholipid bilayer (hydrophilic phosphate head and hydrophobic fatty acid tail) - cell membrane
● tails can splay outwards - waterproofing
● centre of bilayer is hydrophobic so water soluble substances can’t easily pass through it - membrane acts as barrier
compare phospholipids and triglycerides (4)
● both have glycerol backbone
● both may be attached to mixture of saturated, monounsaturated and polyunsaturated fatty acids
● both contain elements C, H, O
● both formed by condensation reactions
contrast phospholipids and triglycerides (3)
● triglycerides have 3 fatty acids attached whereas phospholipids have 2 fatty acids and 1 phosphate group attached
● triglycerides entirely hydrophobic whereas phospholipids have hydrophilic head and hydrophobic tail
● triglycerides used as energy storage molecules whereas phospholipids are used in membrane formation
are phospholipids and triglycerides polymers? (2)
● no
● they are macromolecules
describe the emulsion test for lipids (5)
● crush sample
● add ethanol
● pour into water and shake
● positive result: milky white emulsion forms
● more lipid there is the more noticeable milky colour will be
