4.4: Lipids

Question 1

What is the general chemical structure of lipids?

Answer 1

They consist mainly of carbon, hydrogen and with a few oxygen-containing functional group

Question 2

What are the general properties of lipids?

Answer 2

1. Do not have polymer
2. Greasy or oily
3. Insoluble in water
4. Soluble in organic solvents

Question 3

Give three importance of lipids.

Answer 3

1. As heat insulator
2. A plasma membrane component
3. Cushioning for internal organs

Question 4

What are the major classes of lipids?

Answer 4

Triacylglycerol, waxes, steroids and phospholipids

Question 5

What is triacylglycerol?

Answer 5

Three carbon skeleton with a hydroxyl group attached to each combined with a long unbranched hydrocarbon chain with carboxyl group at one end

1 glycerol + 3 fatty acids

Question 6

What is a saturated fatty acid?

Answer 6

A straight chain of fatty acid tail with no carbon double bonds. Solid at room temperature and increases cholesterol in blood

eg: palmitic acid, stearic acid, fat, butter

Question 7

What is an unsaturated fatty acid?

Answer 7

Has one or more adjacent pairs of C atoms joined by double bond. Has a kink at double bond and is liquid at room temperature. Decreases cholesterol in blood

eg: oleic acid, linoleic acid, olive oil, fish oil

Question 8

What is the formula for phospholipid?

Answer 8

2 fatty acids + glycerol attached to phosphate group

Question 9

Which one is hydrophilic and hydrophobic in a phospholipid?

Answer 9

The fatty acid tail is hydrophobic while the phosphate group and its attachments form a hydrophilic head

Question 10

How are phospholipids arranged at the surface of a cell?

Answer 10

Bilayer. The hydrophilic heads on the outside are in contact with the aqueous solution while the hydrophobic tails form the core inside

Question 11

What are the importance of phospholipids in living organisms?

Answer 11

Basic component of cell membranes and the boundary between the cell and its external

Question 12

How are steroids identified?

Answer 12

Its carbon skeleton has four fused rings

Question 13

What are the properties of steroids?

Answer 13

1. Characterised as a lipid due to its hydrophobic and insoluble in water properties
2. Has various types of steroids due to various functional group that is attached to the rings

Question 14

What are the importance of steroids?

Answer 14

1. Cholesterol - essential component of animal cell membranes
   - precursor for the synthesis of other steroids
2. Testosterone - stimulates sperm formation
   - responsible for secondary sex characteristics
3. Estrogen - stimulates egg production
   - starts menstrual cycle

Question 15

Give three side effects of steroid abuse in sports and health

Answer 15

1. Renal failure
2. Impotence in males
3. Causes male pattern baldness, cysts, acne, oily hair and skin

Question 16

What is the meaning of waxes?

Answer 16

They are long fatty acids connected to alcohol by ester linkages

Question 17

What are the properties of waxes?

Answer 17

1. Insoluble in water and difficult to hydrolyse
2. Synthesised by animals and plants
3. Found as protective waterproof coatings on leaves, stems, animal fur