1-3 Lipids

Question 1

What are lipids?

Answer 1

• Lipids are biological molecules made of carbon, hydrogen and oxygen which are only soluble in organic solvents such as alcohols.
• Main lipid types are triglycerides and phospholipids

Question 2

What are Triglycerides?

Answer 2

• Triglycerides are lipids made of one molecule of glycerol and three fatty acids joined by ester bonds formed in condensation reactions.
• 3 fatty acids + 1 glycerol

Question 3

What are saturated lipids?

Answer 3

• Animal fats, don’t contain any carbon-carbon double bonds.

Question 4

What are unsaturated lipids?

Answer 4

• Plants, contain carbon-carbon double bonds.
• Presence of carbon-cabron double bonds allows unsaturated lipid to bend meaning that they cannot pack together as tightly and are therefore liquid at room temperature.

Question 5

Describe how triglyceride’s structure relates to its properties?

Answer 5

• High ratio of energy storing carbon-hydrogen bonds
• Low mass to energy ratio meaning that they are a good compact storage molecule. This is beneficial for animals as it is less mass to move around.
• Large and non-polar are insoluble in water so energy storage doesn’t affect wp of cells.
• High ratio of hydrogen-oxygen atoms means that triglycerides release water when they are oxidised and therefore provide an important source of water for organisms to live in dry environments.

Question 6

What are phospholipids?

Answer 6

• Same as triglycerides but one of the fatty acids is substituted by a phosphate-containing group.
• Phosphate heads are hydrophilic, and the tails are hydrophobic and as a result phospholipids form micelles when they are in contact with water. The molecule is therefore known as polar.

Question 7

Describe how phospholipid’s structure relates to its properties?

Answer 7

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

Question 8

What is the emulsion test?

Answer 8

• An emulsion test can be used to test for the presence of lipids.
• 1. Take a test tube and add sample and ethanol
• 2. Shake until sample is dissolved in ethanol
• 3. Add water and shake
• 4. Cloudy white colour indicates presence of lipid
• 5. Repeat experiment with water as control and should stay clear.