OCR A-Level Biology (Lipids)

Functions of Lipids

waterproof (waxy coating)
lipid coating on nerve cells
Buoyoncy
protection
insulation
cell membranes
energy store
hormones

What are the 3 types of lipids

Triglycerides
Phospholipids
Sterols

Describe the emulsion test.

In a test tube add a sample and ethanol, shake lightly, a positive result will show a cloudy emulsion and a negative result will be colourless.

What is the structure of a triglyceride?

Glycerol and 3 fatty acids
joined via condensation reactions
joined by ester bonds

How can triglycerides differ?

Number of double bonds
Hydrocarbon chain length

saturated fatty acid

No double bonds

unsaturated fatty acid

One double bond

polyunsaturated fatty acid

Multiple double bonds

Properties of saturated fats

form solids at room temp
closely packed together

Properties of unsaturated fats

liquids at room temp
can't closely pack together
lower melting and boiling points

which type of triglyceride is healthiest?

polyunsaturated

Structure of a phospholipid

glycerol, 2 fatty acids and a phosphate group

Properties of the phosphate group

Polar, Hydrophillic

Properties of the fatty acid tails

non-polar, hydrophobic

What do phospholipids do at cell membranes?

Form phospholipid bilayers

Functions of phospholipids

help us absorb vitamins in digestion
used in genetic therapy

How can you identify sterols?

4 carbon rings

Properties of the hydroxyl group in sterols.

polar, hydrophilic

Functions of cholesterol

Used to make vitamin D
Used to make bile
Used to make sterol hormones
Strengthens cell membranes

What is the main use of triglycerides

Energy store