Lipids - Biological Molecules Flashcards
Describe the emulsion test for lipids
- dry and grease free test tube
- add ethanol to sample
- shake tube to dissolve
- add water and shake
- cloudy white colour indicates the presence of a lipid
- a negative test shown by a clear solution
(if testing a sold crush/grind before dissolving)
What elements do lipids contain?
Carbon, hydrogen and oxygen
But lower ratio of O to C and H than carbs
Are lipids soluble?
Non-polar molecules
So insoluble in water
But soluble in alcohols and acetone (organic solvent)
What are other properties of lipids?
Generally hydrophobic
Don’t form polymers
What are the types of lipids?
Triglycerides - fats and oils
Phospholipids - found in cell-surface membrane
How is triglyceride an energy + water source?
- energy and metabolic water source
- when oxidise provide more that twice the energy than the same mass of carbs and release valuable water
How are triglycerides buoyancy aids?
- called blubber in aquatic animals and used a buoyancy aid
- less dense than muscle or bone
How are triglycerides insulation?
- heat: slow conductors of heat
- electrical: myelin sheath around nerve cells helps speed up transmission of impulse
How are triglycerides waterproof?
- insoluble in water and useful in providing waterproof protection
- mammals produce waterproof layer from skin
How are triglycerides used as protection?
- fat stored around delicate organs e.g. kidney
- cuticle of lead
What do triglycerides consist of?
3 fatty acids and glycerol (see notes for diagram)
How is glycerol shown?
(See notes)
Sometimes written as
CH2OH
I
CH2OH
I
CH2OH
What do fatty acids consist of?
Carboxyl group (COOH)
Hydrocarbon chain
What do variations in properties come from?
As glycerol is always the same, variations in properties in different fats and oils come from variations in the fatty acids.
What are fatty acids?
There are over 70 different fatty acids
All have an acidic COOH group and hydrocarbon chain attached (R group)
What are saturated fatty acids?
Hydrocarbon chain has only single bonds (between carbon atoms)
What are unsaturated fatty acids?
Hydrocarbon chain has at least one double bond (between carbon atoms)
What are the properties of saturated fatty acids?
-long straight chains
- most animal fats
- solid at room temp
What are the properties of unsaturated fatty acids?
-plant and fish fats
- vegetable oils
- liquid at room temp
- kinks made by double bonded C prevent molecules from packing tightly together
What reaction takes place between fatty acids and glycerol?
A condensation reaction occurs between glycerol and fatty acids to form an ESTER BOND
Where must water molecules come from in the condensation reaction?
H from OH group on glycerol
OH from carboxyl group on fatty acids
Must be from exact positions
Explain emulsion test for lipids
Lipid will dissolve in ethanol
But will not in water -forming cloudy white emulsion
How is structure related to function for triglycerides?
Pt 1
High proportion of C-H bonds for number of C atoms (bonds store energy)
- excellent source of energy
High proportion of H to O atoms
- release water when oxidised, so useful source of water (especially for animals living in dry climates)
Large non polar molecules making them insoluble
- storage doesn’t affect the water potential of the cell and so no effect on osmosis
How is structure related to function of triglycerides?
Low mass to energy ratio
- good storage molecule because a great deal of energy can be stored in a small volume
Draw condensation reaction between triglyceride and phosphoric acid to make a phospholipid
See notes
What is the structural difference between a triglyceride and a phospholipid?
One of the fatty acids is replaced by a phosphate group
Shown as P
What are the properties of phospholipids?
- phosphate is -vely charged and attracts water HYDROPHILIC
- fatty acid molecules are HYDROPHOBIC and repel water
- a phospholipid has a
HYDROPHILIC HEAD
HYDROPHOBIC TAIL
What is the structure of a phospholipid?
Polar head
Attracts water
Hydrophilic
Fatty acid tails
Repels water
Hydrophobic
What are the adaptations to function (phospholipid)? Bilayer
- polar molecule with hydrophilic head and hydrophobic tail with 2 fatty acids
- in aqueous environment molecules form a bilayer within cell-surface membrane
- forms a hydrophobic barrier between inside and outside of cell
What are the adaptations to function (phospholipid)? Micelles
- can self-assemble into micelles
- useful in the absorption of molecules that aren’t easily soluble
What are the adaptations to function (phospholipid)? Glycolipids
- structure allows them to combine with carbohydrates within cell-surface membrane to form glycolipids
- important in cell recognition
