3.1.3 Lipids Flashcards
What are lipids made of?
Carbon, hydrogen and oxygen
Proportion of oxygen to carbon and hydrogen is…
Smaller than in carbs
Solubility in water and why
Insoluble-lipids are non-polar molecules while water is polar molecule, so there is no way for water to attach to a lipid molecule. Instead, the non-polar lipids will bind to themselves, which is why oils and fats form droplets on the surface of water
Solubility in organic solvents e.g alcohols, acetone
Soluble
What are the two main groups-draw them (if paper not available draw in air)?
Triglycerides (fats and oils)
Structure- Glycerol attached to fatty acid chains
Phospholipids (make up cell (plasma) membranes
Structure- Phosphate head, glycercol attached to fatty acid chains
What do phospholipids contribute to?
The flexibility of membranes and the
transfer of lipid-soluble substances across them
Roles of lipids
source of energy- when oxidised, lipids provide more than TWICE energy as the same mass of carbs + release valuable water.
waterproofing- lipids are insoluble in water, plants+insects have waxy, lipid cuticles- conserve water, while mammals produce an oily secretion from the sebaceous glands in the skin.
insulation- fats are slow conductors of heat and when stored beneath the body surface help to retain body heat. Also act as electrical insulators in the myelin sheath around nerve cells.
protection- often around delicate organs e.g kidneys
Triglycerides have…
Three fatty acid groups
One glycerol group
What bonds do the fatty acids form with the glycerol?
An ester bond in a condensation reaction
What does hydrolysis of triglyceride produce?
Glycerol and fatty acids
Where do the different properties come from?
The variations in fatty acids- glycerol molecules are always the same
How many fatty acids are there?
Over 70
All triglycerides have
Carboxyl (-COOH) group with hydrocarbon chain attached and vary in lengths and bonds
What does saturated mean?
The hydrocarbon chain contains no double carbon-carbon bonds?
What does mono-unsaturated mean?
The hydrocarbon chain has one double carbon-carbon bond
What does poly-unsaturated mean?
The hydrocarbon chain has more than one double carbon-carbon bond
What do the double bonds cause?
the molecule to bend. They cannot therefore pack
together so closely making them liquid
at room temperature. i.e. they are oils
Structure of triglycerides related to their properties
High ratio of energy storing carbon-hydrogen bonds to carbon atoms so an excellent source
of energy.
Low mass to energy ratio- so good storage molecules as much energy can be stored in a small volume
Large, non-polar molecules- insoluble in water, doesn’t affect osmosis or water potential in cells
High ratio of hydrogen to oxygen atoms- release water when oxidised
Why are triglycerides properties beneficial to animals?
HROESingCHBCA- excellent energy source
LNPM-their storage doesn’t affect osmosis in cells or
the water potential of them
LMER- Reduces mass that needs to be carried
HRHOA- an important source of water, especially for organisms living in dry deserts.
Compare and contrast saturated/unsaturated fatty acids
Saturated- only single c-c bonds, straight chain molecules w/more contact points, higher m.p=solid at room temp, in animals
Unsaturated- double c-c bonds, kinked molecules w/fewer contact points, found in plant oils
Describe the structure of the phospholipid bilayer
A phosphate hydrophilic head, glycerol molecule, two fatty acids (hydrocarbons) so hydrophobic
Structure of phospholipids related to properties
Polar molecule (philic head, phobic tail)- aqueous environment, form a bilayer within cell-surface membranes- hydrophobic barrier
formed between the inside and outside of a cell.
Hydrophilic phosphate ‘heads’ -
to hold at the surface of the cell-surface membrane
Phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane
Emulsion 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 liquid in the sample
Add 5cm3 of water and shake gently
A milky-white emulsion indicates the presence of a lipid
(Simple- Sample+ethanol-shake-add water-shake-milky white emulsion)
Function of the phospholipid bilyaer
Allows lipid soluble substances to
enter and leave cells
Prevents water soluble
substances entering and leaving
cells
Makes the membrane flexible
Compare phospholipids and triglycerides.
● Both have glycerol backbone. ● Both may be attached to a mixture of saturated, monounsaturated & polyunsaturated fatty acids. ● Both contain the elements C, H, O. ● Both formed by condensation reactions.
Contrast phospholipids and triglycerides.
phospholipids: ● 2 fatty acids & 1 phosphate group attached ● Hydrophilic head & hydrophobic tail ● Used primarily in membrane formation
triglycerides: ● 3 fatty acids attached ● Entire molecule is hydrophobic ● Used primarily as a storage molecule (oxidation releases energy)
Are phospholipids and triglycerides
polymers?
No- they aren’t made from a small repeating unity- they’re macromolecules
