Lipids

Question 1

How is the structure of a triglyceride related to its property?

Answer 1

• insoluble in water so their storage does not effect water potential
• low mass to energy ratio - lots of energy can be stored in a low volume
• lots of energy storing bonds - good source of energy

Question 2

How is the structure of a phospholipid related to its property?

Answer 2

• polar so form a bilayer in cell surface membranes
• hydrophilic heads hold the molecule at the surface of the membrane
• structure allows them to combine with carbohydrates to form glycolipids - needed for cell detection

Question 3

What is a saturated fatty acid?

Answer 3

Only contains single carbon carbon bonds within the R group (hydrocarbon chain) and has no double bonds

Question 4

What is a mono-unsaturated fatty acid?

Answer 4

Has a single carbon carbon double bond within the R group (hydrocarbon chain)

Question 5

What is a poly-unsaturated fatty acid?

Answer 5

Has 2 or more carbon carbon double bonds within the R group (hydrocarbon chain)

Question 6

What bond is formed in the condensation reaction between glycerol and fatty acids?

Answer 6

Ester bond

Question 7

What products are formed in the condensation reaction between glycerol and fatty acids?

Answer 7

Triglyceride molecule + 3H20

Question 8

What is a triglyceride?

Answer 8

A molecule consisting of 1 glycerol molecule and 3 fatty acids but is NOT a polymer

Question 9

What is a phospholipid?

Answer 9

A molecule made from 1 glycerol molecule, 2 fatty acids and a phosphate group with hydrophilic heads (negative phosphate group) and hydrophobic tails (fatty acid chain)

Question 10

What are the similarities and differences between triglycerides and phospholipids?

Answer 10

Similarities:

• Both contain 1 molecule of glycerol
• Both contain 2 fatty acids
• Both bonded with ester bonds

Differences:

• Phospholipids contain elements C,H,O and P whereas triglycerides contain only C,H and O
• Phospholipids have 2 fatty acids whereas triglycerides have 3
• Phospholipids form a bilayer in water (micelle) whereas triglycerides do not
• Phospholipids are hydrophilic AND hydrophobic whereas triglycerides are ONLY hydrophobic

Question 11

What is the biochemical test for lipids?

Answer 11

• Add 5cm^3 ethanol to 2cm^3 sample
• Shake the tube thoroughly to dissolve any lipid in the sample
• Add 5cm^3 water and shake gently
• Positive result: cloudy white emulsion
  Negative result: stays clear and colourless