1.3 Lipids

Question 1

What are the common characteristics of lipids?

Answer 1

1. Contain carbon, hydrogen and oxygen
2. The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
3. Insoluble in water
4. Soluble in organic solvents (e.g. alcohol and acetone)

Question 2

What is the role of a phospholipid?

Answer 2

Contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them

Question 3

What states are fats and oils when at room temperature (10-20•C)

Answer 3

Fats are solid; oils are liquid

Question 4

In a triglyceride, what bond forms between each fatty acid and glycerol?

Answer 4

Ester bond

Question 5

How many water molecules are involved in the condensation and hydrolysis of a triglyceride?

Answer 5

3 water molecules

Question 6

What is a saturated fatty acid?

Answer 6

A fatty acid with no carbon-carbon double bonds. This state is described as saturated as all carbon atoms are bonded to the maximum possible number of hydrogen atoms.

Question 7

What is a mono-unsaturated fatty acid?

Answer 7

When there is a single carbon-carbon double bond

Question 8

What is a poly-saturated fatty acid?

Answer 8

When there are multiple carbon-carbon double bonds present in a fatty acid.

Question 9

What is the structure of a phospholipid?

Answer 9

Two fatty acids and one phosphate molecule

Question 10

Is the phosphate ‘head’ hydrophilic or hydrophobic?

Answer 10

The hydrophilic ‘head’ is attracted to water and repelled by fat

Question 11

Is the fatty acid ‘tail’ hydrophilic or hydrophobic?

Answer 11

The hydrophobic ‘tail’ is repelled by water but attracted to fat

Question 12

As phospholipids are polar molecules, how would they behave in an aqueous environment?

Answer 12

Phospholipids form a bilayer within cell-surface membranes; the head faces outwards towards the environment, whilst the tail remains in the middle. This forms a hydrophobic barrier formed between the inside and outside of a cell.