Lipids

Question 1

Lipids

Answer 1

C,H,O
insoluble in water
main groups are triglycerides

Question 2

roles of lipids

Answer 2

Bilayer in cell surface membrane
Source of energy- When oxidised, lipids provide twice the energy as carbohydrates and release water
Waterproofing- Lipids are insluble in water. so a layer could water proof it
Insulation- Fats are slow conductors of heat so they store heat under the skin.
electrical insulators in mylein sheath of neurones
Protection- Fats are stored around organs
Fats are solid at R.T
oils are liquid at R.T

Question 3

Triglycerides

Answer 3

Have three fatty acids and one glycerol
each fatty acid forms an ester bond with the glycerol
variations between triglycerides come from different fatty acids
more than 70 fatty acids
all have a carboxyl group(COOH)
If the hydrocarbon chains have a C-C double bonds they are unsaturated(oils, liquid at R.T)
If they do not, they are saturated
mono-unsaturated
poly-unsaturated

Question 4

The structure of triglycerides related to their properties

Answer 4

High ratio of energy storing C-H bonds(EXCELLENT source of energy)
low mass to energy ratio making them good storage molecules. reduces mass to be carried
large,non-polar means unsoluble
high ratio of H-O atoms.provide important source of water.

Question 5

Phospholipids

Answer 5

Similar to lipids but one fatty acid is replaced by a phosphate molecule
Fatty acid tail-hydrophobic
Phosphate head-hydrophilic
Therefore,polar

Question 6

Structure of phopholipids related to their properties

Answer 6

Forms a bilayer due to its polar nature
Heads help to hold at the surface of the cell-surface membrane
Form glycolipids by combining carbohydrates within cell-surface membranes. Important in cell recognition

Question 7

Test for lipids

Answer 7

2cm3 of sample
Shake
5cm3 of ethanol
Shake and add 5cm3 of water
Cloudy white colour indicates lipids
Reason- light is refracted by the dispersed lipids