Biological Molecules - Lipids Flashcards
what are lipids and what do they contain
lipids are macromolecules. they contain large amounts of carbon and hydrogen atoms with fewer oxygen atoms.
what are lipids soluble and insoluble in
lipids are soluble in organic solvent (e.g alcohol)
and insoluble in water
what are the three important groups of lipids
triglycerides (fats and oils)
phospholipids
cholesterol
give an example of lipids functioning as energy storage
adipose tissue of vertebrates, oil in fruits and seeds
give an example of the structural function of lipids
phospholipid bilayer of cell membrane
give an example of the thermal insulation function of lipids
to reduce heat loss e.g penguins
give an example of the electrical insulation function of lipids
myelin sheath of neurone axons
give an example of the cushioning/protection function of lipids
to protect vital organs e.g heart and kidneys
give an example of the waterproofing function of lipids
birds feathers and plant leaves
give an example of the buoyancy function of lipids
aquatic animals like whales
give an example of lipids functioning in hormone production
testosterone, oestrogen, cortisol
describe the structure of triglycerides
one molecule of glycerol attached to three fatty acids by ester bonds
describe the structure of glycerol
alcohol with three carbons and 3 OH groups
describe the structure of fatty acids
carboxyl group: COOH
hydrocarbon tail: carbon and hydrogen, varies in length and structure (2-20 carbons long)
give a property of fatty acids
hydrophobic - making them insoluble in water
describe saturated fatty acids
all of the carbon atoms form the maximum number of bonds with hydrogen atoms. there are NO double bonds between carbon atoms
describe unsaturated fatty acids
there is at least one double bond between carbon atoms. this causes the chain to kink
describe monosaturated fatty acids
there is just one double bond
describe polysaturated fatty acids
there are two or more double bonds
why are polyunsaturated fats liquid at room temperature
the kinks caused by double bonds mean that the molecules cannot pack as closely together
how are triglycerides formed
a condensation reaction occurs between the COOH group of the fatty acid and the OH group of the glycerol.
the bond formed is an ester bond
what is the name for the reaction forming triglycerides
esterification
how can triglycerides be broken down
the ester bonds can be broken down by hydrolysis reactions
what is the main function of triglycerides
compact energy store
why are triglycerides a good compact energy store
they contain a high proportion of C-H bonds and therefore release about twice as much energy per gram as carbohydrates
why are triglycerides insoluble in water and why is this useful
they are non-polar. therefore, they do not affect osmosis in cells
why are lipids useful for desert animals
respiration of lipids releases water
what other functions do triglycerides have (5)
thermal insulation, buoyancy (less dense than water), electrical insulation, protection, storage of fat-soluble vitamins e.g A and D
describe the structure of phospholipids
similar to triglycerides but a phosphate group replaces one of the fatty acids ie one molecule of glycerol attached to a phosphate group and two fatty acids
describe the phosphate group in phospholipids
negatively charged polar head. hydrophilic
describe the fatty acid chains in phospholipids
uncharged, non-polar tails. hydrophobic
what are the three behaviours of phospholipids in water
- form a single layer on water with their heads in the water and their tails sticking up
- form micelles in water: tiny balls with the tails pointing in and the heads on the outside
- bilayer can form with two rows of phospholipids: tails pointing inwards and heads outwards
describe the main function of phospholipids
form a key role in cell membranes
why are phospholipids useful in cell membranes
flexibility and stability: the phospholipids can move within a layer but not out of the layer
selective permeability: the non-polar tails makes the membrane a barrier to the movement of large polar molecules, but small and non-polar molecules can diffuse through
why do organisms living in colder climates often have an increased number of unsaturated fatty acids in their phospholipid membranes
more kinked molecule; less uniformly packed together, ensures fluidity of membranes at lower temperatures
describe the structure of cholesterol
a sterol; a lipid not made from fatty acids and glycerol
cholesterol is a small hydrophobic molecule
what are the functions of cholesterol
found in cell membranes where it regulates fluidity
Vitamin D, steroid hormones e.g testosterone, and bile are manufactured from cholesterol
how can the substances manufactured from cholesterol pass through the cell surface membranes
simple diffusion
describe the method for the emulsion test for lipids
crush material and mix well with ethanol
decant or filter the suspension to remove any solid particles
carefully pour the ethanol solution onto some water in a clear test tube - don’t mix
what are the positive and negative results for the emulsion test
positive: a milky white emulsion forms on top of the water
negative: solution remains clear
why will the emulsion test not work for milk
milk will cause the solution to appear milky white regardless of whether or not there are lipids present
how does the emulsion test for lipids work
lipid is dissolved in ethanol and water is mixed with lipid and ethanol solution
water is more soluble than lipids in ethanol, so water displaces lipid from ethanol, forming the suspension as lipids are insoluble in water
