Lipids Flashcards
characteristics of lipids
they contain carbon hydrogen and oxygen
the proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
they are insoluble in water
they are soluble in organic solvents such as alcohols and acetone
what are the main groups of lipids
triglycerides
phospholipids
explain the role of the lipids in the cell membrane
phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them
state all the roles of lipids
source of energy
water proofing
insulation
protection
cell membranes
explain how lipids can be used as a source of energy
when oxidised lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water
explain how lipids are used for waterproofing
Lipids are insoluble in water and therefore useful as water proofing
both plants and insects have waxy, Lipid cuticles that conserve water, while mammals produce an oily secretion from the sebaceous glands in the skin
explain how lipids are used for insulation
Fats are slow conductors of heat and when stored beneath the body surface help to retain body heat
they also act as electrical insulators in the myelin sheath around nerve cells
explain how lipids are used for protection
fat is often stored around delicate organs, such as the Kidney
Describe triglycerides
they have three fatty acids combined with glycerol
Each fatty acid forms an ester bond with glycerol in a condensation reaction
hydrolysis of a triglyceride therefore produces glycerol and three fatty acids
how many fatty acids are there
70 different fatty acids
what do all fatty acids have
carboxyl group with a hydrocarbon chain attached
when are the fatty acids described as saturated
if this chain has no carbon-carbon double bonds, the fatty acid is then described as saturated, because all the carbon atoms are linked to the maximum possible number of hydrogen atoms
when are the fatty acids described as mono-unsaturated
if the is a single double bond, it is mono-unsaturated
when are the fatty acids described as polyunsaturated
if more than one double bond is present, it is polyunsaturated.
these differences are illustrated
how are high ratio energy storing, carbon-hydrogen good for storing energy
triglycerides have a ratio of energy-storing carbon-hydrogen bonds to carbon atoms and are therefore an excellent source of energy
explain the benefits of triglycerides having a low mass-to-energy ratio
triglycerides have a low mass to storage ratio making them good storage molecules because much energy can be stored in a small volume
this is especially beneficial to animals as it reduces the mass they have to carry as they move around
explain the benefits of triglycerides being large
being large, non-polar molecules, triglycerides are insoluble in water.
As a result their storage does not affect osmosis in cells or the water potential of them
explain the benefits of triglycerides having a high ratio of hydrogen to oxygen atoms
triglycerides release water when oxidised and therefore provide an important source of water, especially for organisms living in dry deserts
how are phospholipids different to triglycerides
one of the fatty acid molecules is replaced by a phosphate molecule.
whereas, fatty acid molecules are hydrophobic, phosphate molecules are hydrophillic
what are phospholipids made up of
a hydrophilic ‘head’, which interacts with water but not with fat
A hydrophobic ‘tail’ which orients itself away from water but mixes readily with fat
what does it mean when molecules are described as polar
molecules that have two ends that behave differently in this way are said to be polar
explain what happens when these polar phospholipid molecules are placed in water
they position themselves so that the hydrophilic heads are close to the water as possible and the hydrophobic tails are as far away from the water as possible
why are polunsaturated triglycerides liquid at room temperature
the double bonds cause the molecule to bend.
they cannot therefore pack together closely making them liquid at room temp
explain the result of phospholipids being polar molecules
they have a hydrophilic phosphate head and a hydrophobic tail of two fatty acids
this means that in an aqueous environment, phospholipid molecules form a bilayer within cell-surface mambrances
as a result, a hydrophobic barrier is formed between the inside and outside of a cell
benefits of the hydrophilic phosphate heads
the hydrophilic phosphate heads of phospholipid molecules help to hold at the surface of the cell-surface membrane
what does the phospholipid structure allow them to do
allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane
these glycolipids are important in cell recognition
describe the test for lipids
take a completely dry and grease-free test tube
to 2cm3 of the sample being tested, add 5cm3 of ethanol
shake the tube thoroughly to dissolve any lipid in the sample
add 5 cm3 of water and shake gently
a milky white color indicates the presence of a lipid
as a control repeat the procedures using water instead of the sample; the final solution should remain clear
what is the test for lipids known as
the emulsion test
why is there a cloudy color during the test
the cloudy colour is due to any lipid 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
