3.1.3 lipids Flashcards
describe the test for lipids = emulsion test
- take a completely dry and grease free test tube
- 2cm3 of the sample being tested, add 5cm3 of ethanol
- shake the test tube througly to disolve any lipid in the sample
- add 5cm3 of water and shake gently
- a cloudly-white colour indicates the prescense of a lipid
- as a control, repeat the procedures using water instead of the sample, the final solution should remain clear
what are the structure of phospholipids + properties?
polar molecules = hydrophillic head phosphate molecule and hydrophobic tail of two fatty acids
form a phosopholipid bilayer within cell surface membranes
hydrophillic phosphate heads help to hold the surface of the cell surface membrane
phosopholipid structure allows them to form glycolipids by combining with carbohydrates within the cell surface membrane
glycolipids are important in cell recognition
what are the substances fats produce?
essential fatty acids = that the body needs but cannot make (synthesized)
for soluable vitamins (A, D, E and K) can only enter our diet dissolved in fats
describe the structure of phospholipids
similiar to lipids expect one of the fatty acids molecules is replaced by a negatively charged phosphate molecule
phosphate molecules are hydrophillic = attract water
phospholipids have 2 parts:
1. hydrophillic head = interacts with water but not with fat
2. hydrophobic tail = orients itself away from water but interacts with fat
in cell membranes
what are the functions of cholesterol?
short lipid molecule
cell membranes
sex hormones
made in liver from saturated fats
too high cholesterol can cause CVD’s
what bond does unsaturated fats have?
mono saturated fats = double bond
poly unsaturated fats = larger number of double bonds
double bond = kink
kink prevents close packing so weaker intermolecular forces and liquid at room temperature
summary for saturated fats
if the fatty acid chains in a lipid contains the maximum number of hydrogen atoms
in a saturated fat the hydrocarbon chain is long and straight
no carbon to carbon double bonds
no more hydrocarbon can be added
animal fats and dairy products
straight saturated chains pack closely, strong intermolecular bonds between tryglicerides result in fats becoming solid at room temperature
what is the fatty acid structure?
r ———- c ————- oh
|
o
r group is a hydrocarbon chain
carboxyl group (COOH) forms the acid
describe the structure of triglycerides + properties
triglycerides have a high ratio of energy storing carbon-hydrogen bonds to carbon atoms and therefore an excellent source of energy
have low mass to energy ratio, making them good storage molecules because a lot of energy can be stored in small volumes
large non-polar molecules so insoluable in water.
storage is not affected by osmosis in cells or the water potential in them
high ratio of hydrogen to carbon atoms = triglycerides release water when oxisidised and therefore provide an important source of water eg animals living in deserts
what are fatty acids?
70 different fatty acids
all have a carboxyl group with a hydrocarbon chain attached
saturated fatty acids = no carbon-carbon double bonds (carbon atoms are linked to the maximum number of hydrogen atoms)
mono-unsaturated = single double bond
polyunsaturated = one double bond
what are triglycerides?
most common lipid
3 fatty acids and one glycerol molecule
bond between each fatty acid + glycerol = ester bond
linked by condensation reaction
describe lipids
enhance palability of food
twice the gram of energy per food than carbohydrates
large amount of energy can be stored in a small mass
organic molecule
insoluable in water and soluable in organic solvents
what are the role of lipids?
source of energy = lipids provide more than twice the energy as the same mass of carbohydrates
waterproofing = lipids are insoluble in water eg waxy lipid cuticles on plants
insulation = fats are slow conductors of heat and stored below body surface to retain heat
protection = stored around delicate organs eg kidney
