Lipids

Question 1

Name the two main groups of Lipids

Answer 1

Triglycerides

Phospholipids

Question 2

Describe the structure of triglycerides

Answer 2

One glycerol molecule bonded to three fatty acids. An ester bond is present between each fatty acid chain and the single glycerol molecule.

Question 3

Describe the structure of a phospholipid

Answer 3

One glycerol molecule, bonded to two fatty acids and one Phosphate group.

Question 4

Fatty acids can be….

Answer 4

Saturated or Unsaturated.

Question 5

Describe a saturated fatty acid

Answer 5

A fatty acid with no double bonds between C atoms in the Carbon skeleton.

Question 6

Describe an unsaturated fatty acid.

Answer 6

A fatty acid which contains one or more double bonds between C atoms in the Carbon skeleton.

Question 7

Why are unsaturated fats liquid at room temperature?

Answer 7

The double bonds within the Carbon skeleton cause the molecules to kink, so they cannot pack together so closely.

Question 8

Describe the properties of lipids.

Answer 8

Excellent source of energy due to a high number of C-H bonds.

Excellent storage molecules because they have a low mass to energy ratio.

Insoluble in water so do not affect water potential of cells.

Soluble in organic solvents such as alcohol and acetone.

Question 9

Phosphate heads of phospholipids are..?

Answer 9

Hydrophilic

Question 10

The fatty acid tails of phospholipids are..?

Answer 10

Hydrophobic

Question 11

Are phospholipids polar or non-polar?

Answer 11

They are polar

Question 12

Roles of phospholipids

Answer 12

Make up the plasma membrane in cells, a hydrophobic bilayer.

The more unsaturated fatty acids present within the phospholipids, the more fluid the membrane is.

They can combine with carbohydrates to form glycolipids, important in cell recognition.

Question 13

Describe the emulsion test for the presence of lipids in a sample.

Answer 13

Add 5cm cubed ethanol to 2cm cubed of the sample

THEN add 5cm cubed of water

A positive result is a milky-white emulsion