1.3 Lipids

Question 1

What are lipids

Answer 1

Biological molecules made of carbon, hydrogen, oxygen and some contain phosphorous.

Question 2

What are triglycerides and how are they formed

Answer 2

• Lipids made of one molecule of glycerol and 3 fatty acids.
• They are joined by ester bonds formed in condensation reactions.

Question 3

What are saturated lipids

Answer 3

• Lipids that don’t contain any carbon-carbon double bonds.
• Often solid at room temperature.

Question 4

What are unsaturated lipids

Answer 4

• Lipids that contain at least one carbon-carbon double bond.
• This means the molecule is able to bend.
• They cannot pack together as tightly as saturated fats, so are liquid at room temperature

Question 5

How is the structure of triglycerides related to their function

Answer 5

• High ratio of energy storing carbon-hydrogen bonds to carbon atoms: excellent energy store
• Low mass to energy ratio: good storage molecule with a lot of energy being stored in a small volume (less mass to move around, so beneficial for animals.)
• Large and non-polar: insoluble in water, so their storage does not affect the water potential of cells.
• High ratio of hydrogen-oxygen atoms: release water when they are oxidised, so provide an important source of water for organisms to live in dry environments.

Question 6

Describe the structure of a phospholipid

Answer 6

• One molecule of glycerol
• Phosphate group (head) - hydrophylic
• 2 fatty acids (tails) - hydrophobic
• Polar molecule (phosphate group is charged)
• Form micelles and bilayers in water

Question 7

How are phospholipids related to their function

Answer 7

• In an aqueous environment, being polar means a bilayer can form.
• The hydrophylic heads can be used to hold at the surface of the cell membrane.
• Their structure allows them to form glycolipids and carbohydrates which are important on the cell surface membrane for cell recognition.

Question 8

What is the biochemical test for lipids

Answer 8

1. Take a completely grease free test tube and add 2cm3 of the sample and 5cm3 of ethanol.
2. Shake the test tube thoroughly to dissolve all the lipid in the solution.
3. Add 5cm3 of water and shake gently.
4. A cloudy-white colour indicates the presence of a lipid