Lipids

Question 1

What are lipids?

Answer 1

Lipids contain less oxygen molecules than carbohydrates

They are non-polar & hydrophobic (insoluble in water)

Question 2

There are two groups

Answer 2

Triglycerides - the main component of fats & oils
Phospholipids

Question 3

Non-polar molecule

Answer 3

When electrons are shared equally, so the molecule is not charged

Question 4

Triglycerides have two monomers:

Answer 4

Glycerol is an alcohol (C - OH)

Fatty acids contain a methyl group (-CH3) at one end of the chain, and a carboxyl group at the other end (-RCOOH)

Fatty acids can vary in length and saturation

Question 5

Saturated triglyceride

Answer 5

Hydrocarbon chain is saturated (single bonds of carbon)

Question 6

Monounsaturated triglyceride

Answer 6

1 double bond of carbon in hydrocarbon chain

Question 7

Polyunsaturated triglyceride

Answer 7

More then 1 carbon double bond in the hydrocarbon chain

Question 9

How are triglycerides formed?

Answer 9

By esterification - an ester bond forms when a hydroxyl (-OH) group on glycerol bonds with the carboxyl (-COOH) group of the fatty acid

Three fatty acids join to one glycerol molecule to form a triglyceride

Question 10

Triglyceride function

Answer 10

Protection - triglycerides within adipose tissue protects organs from the risk of damage

Insulation - triglycerides are used to insulate nerve fibres & within adipose tissue below the skin

Buoyancy - the low density of fat tissue helps animals to float more easily

Energy storage - the many C-H bonds can be oxidised in cellular respiration to release lots of energy → used to produce ATP
Plants store triglycerides in the form of oils (within seeds & fruit)
Mammals store triglycerides as oil droplets in adipose tissue (a reserve energy source)

Question 11

The structure of phospholipids

Answer 11

Phospholipids have only two fatty acids

The third has been replaced by a phosphate ion (PO4 3-)

Question 13

The structure of phospholipids

Answer 13

As the phosphate is polar, it is soluble in water (hydrophilic)

The fatty acid ‘tails’ are non-polar and insoluble in water (hydrophobic)

Phospholipids are therefore amphipathic - contains both hydrophobic & hydrophilic parts

Question 14

What does the structure of phospholipids form?

Answer 14

In the presence of water due to the hydrophobic and hydrophilic parts phospholipids will form monolayers or bilayers.

Question 15

Phospholipid function

Answer 15

Phospholipids are the building block of cell membranes
They act as a barrier to water-soluble molecules & can control what substances enter and leave the cell

Different compositions of phospholipids helps to change the fluidity of the cell membrane
Mainly saturated fatty acids - membrane will be less fluid
Mainly unsaturated fatty acids - membrane will be more fluid

Phospholipids also control the orientation of proteins present in the cell membrane
Weak hydrophobic interactions hold proteins in place, but still allow them to move

Question 16

Emulsion test for lipids

Answer 16

Add ethanol and distilled water
If lipids are present, a milky emulsion will form (the solution appears ‘cloudy’); the more lipid present, the more obvious the milky colour of the solution