S1-lipids

Question 1

What characteristics do all lipids share?

Answer 1

• Contain carbon, hydrogen and oxygen
• They are insoluble in water
• Soluble in organic solvents
• Proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates

Question 2

What are the roles of lipids and how do they do those roles?

Answer 2

• Cell membranes - Phospholipids make it more flexible, transfer lipid soluble substances
• Energy source - When oxidised provide over twice the amount of energy as the same mass of carbohydrate, release valuable water
• Waterproofing - Lipids-insoluble in water
• Insulation - slow conductors of heat, act as electrical insulators in myelin sheath around nerve cells
• Protection - stored around delicate

Question 3

How are triglycerides formed?

Answer 3

• 3 fatty acids and glycerol
• Ester bonds
• Condensation reactions

Question 4

What is the same in all triglycerides?

Answer 4

The glycerol molecule

Question 5

How many different fatty acids are there and what are they made up of?

Answer 5

• Over 70
• A carboxyl(-COOH) group
• Hydrocarbon chain

Question 6

What is a saturated fatty acid?

Answer 6

• There are no double bonds between carbons

* Carbon is linked to the maximum number of hydrogen

Question 7

What are the types of unsaturated fatty acids and their properties?

Answer 7

• Mono-unsaturated - one double bond between carbon
• Poly-unsaturated - more than one double bond between carbons.
• Double bonds cause them to bend.
• So cant pack together as closely and saturated.
• Therefore they are liquid at room temperature

Question 8

How is the structure of triglycerides related to their properties?

Answer 8

• High energy-storing carbon-hydrogen bonds to carbon atoms ratio - so good source of energy.
• Low mass to energy ratio - so good storage molecule as a lot of energy can be stored in a small area.
• Large and non-polar - insoluble in water - doesn’t effect osmosis or water potential.
• High ration of hydrogen to oxygen so release water when oxidised - important source of water

Question 9

How are phospholipids similar and different to lipids?

Answer 9

• Similar structure but have 2 fatty acids and glycerol

* One fatty acid is replaced with a phosphate group

Question 10

Describe the structure of a phospholipid

Answer 10

• Made of 2 fatty acids, glycerol and a phosphate group
• Phosphate ‘head’ which is hydrophilic
• Hydrocarbon ‘tail’ which is hydrophobic

Question 11

What are described as polar?

Answer 11

a molecule which has 2 ends with opposite charges

Question 12

How is the structure of phospholipids related to their function?

Answer 12

• Polar molecules- hydrophilic head, hydrophobic tail- in aqueous environments form bilayer in cell-surface membrane- hydrophobic barrier between inside and outside of cell.
• Hydrophilic head help hold at surface of the cell surface membrane.
• Structure allows carbohydrates in cell-surface membrane to combine-forming glycolipids- important in cell recognition

Question 13

What is the test for lipids?

Answer 13

EMULSION TEST

1. Take completely dry, grease-free test tube.
2. And 5cm^3 ethanol to 2cm^3 sample
3. Shake test tube
4. Add 5cm^3 water
5. Shake test tube

Positive test = cloudy white

Question 14

Why does the positive test for lipids occur?

Answer 14

• Lipid is finely dispersed in the water - forms emulsion.
• Light passing through is refracted as it passes from oil droplets to water droplets.
• Making it appear cloudy.