1.5 lipids Flashcards
What are lipids (4 properties)
Substances that share the following:
. Contain carbon, hydrogen, oxygen
. proportion of oxygen to C and H is smaller than in carbohydrates
. They are insoluble in water
. soluble in organic compounds such as alcohols and acetone.
role of phospholipids in cell membranes
. Phospholipids contribute to the flexibility of membranes and the transfer of lipid soluble substances across them
How are lipids a good source of energy compared to carbohydrates
. When oxidised, they provide double the energy as the same mass of carbohydrate, and also release water
Why are lipids used for waterproofing
Give examples of where they’re used
. Insoluble in water
. Plants and insects have waxy lipid cuticles that conserve water
. Mammals produce an oily secretion from sebaceous glands in skin
Why are lipids used in insulation
Give 2 examples of in the body
. Fats are slow conductors of heat, and when stored beneath the body surface, they help retain body heat
. Also act as electrical insulators in the myelin sheath around nerve cells
How are lipids used for protection
. Fat is stored around delicate organs eg kidneys
What are triglycerides made from
What are the bonds holding it together
. Three fatty acids and a glycerol molecule
. Each fatty acid forms an ester bond with glycerol in a condensation reaction
This means hydrolysis of a triglyceride produces 3 fatty acids and 1 glycerol
Structure of triglyceride
CH2OH HOOC—FA1
CHOH + HOOC—FA2
CH2OH HOOC—FA3
Glycerol + 3 fatty acids
—> CH2OOC—FA1
CHOOC—-FA2 +3H2O
CH2OOC–FA3
Why are there different properties of different triglycerides
. In every triglyceride the glycerol molecule is the same
. Different fats and oils come from variations in the fatty acids (there are over 70 types of fatty acids)
Properties of fatty acids
What are saturated ones?
What are unsaturated ones?
-All have a carboxyl group (COOH) with a hydrocarbon chain attached
saturated ones have no carbon double bonds, so all carbon atoms are linked to the max possible number of hydrogen atoms.
Unsaturated ones have one carbon double bond (mono-unsaturated) or more than one (poly-unsaturated)
Why are triglycerides a good source of energy
. Excellent source of energy: High ratio of energy storing carbon-hydrogen bonds to carbon atoms
Why are triglycerides good storage molecules in terms of mass
. Low mass to energy ratio so lots of energy can be stored in a small volume
Beneficial to animals as it reduces the mass they have to carry around
Why are triglycerides insoluble in water
. Large, non polar molecules so their storage doesn’t affect osmosis in cells or the water potential of them
Why do triglycerides release water when oxidised
High ratio oxygen to hydrogen atoms
They provide an important source of water, especially for organisms in desert
What are phospholipids
Same as triglycerides but one of the fatty acids
is replaced by a phosphate molecule
So still contain a glycerol molecule
What two parts of phospholipids are there
Head and tail
Head is hydrophilic whereas tail is hydrophobic
The head is a phosphate whilst the tail is the fatty acids
What part of the phospholipid is hydrophilic
The phosphate molecules are hydrophillic and attract water.
This forms a hydrophilic head which interacts with water
What part of phospholipids are hydrophobic
The tail orients itself away from water, but mixes with fat
How do phospholipids position themselves in water
They are polar so have two ends that behave differently.
When in water, they position themselves so that the hydrophilic heads are as close to water as possible, and hydrophobic tails are as far from water as possible
How do phospholipids form a bilayer
. Phospholipids are polar molecules, with a hydrophilic phosphate head and hydrophobic tail of two fatty acids.
This means that in an aqueous environment, phospholipid molecules form a bilayer within cell-surface membrane
As a result, a hydrophobic barrier is formed between the inside and outside of a cell.
How are glycolipids formed
A phospholipid can combine with carbohydrates within cell surface membrane.
These glycolipids are important in cell recognition
How do you test for lipids
. Take a completely dry and grease free test tube
. To 2cm of sample being tested, add 5cm ethanol
. Shake tube thoroughly
. Add 5cm water
. Shake again
. A cloudy white colour indicates the presence of a lipid
. As a control,
Why do you shake the test tube in a lipid test
To make sure all liquid dissolves in the sample
What can you do as a control when testing for lipids
. As a control, repeat the procedures using water instead of sample: final solution should remain clear
Why is a cloudy sample formed from lipid test
. Due to any liquid in the sample being finely dispersed in the water to form an emulsion.
. Light passing through this emulsion is refracted as it passes from oil droplets to water droplets making it appear cloudy
