1.2.3 - Lipids

Question 1

What are lipids?

Answer 1

large family of organic molecules important in cell membranes and as an energy store in many organisms. They include triglycerides, phospholipids and steroids

Question 2

What are fats and oils made up of?

Answer 2

glycerol and fatty acids

combined using ester bonds

Question 3

what is the structure of fatty acids?

Answer 3

long hydrocarbon chain

and a carboxyl group at one end (-COOH)

Question 4

What is an unsaturated fatty acid?

Answer 4

the carbon chains have one or more double covalent bonds in them
can be monounsaturated fatty acid (one double bond)
can be polyunsaturated fatty acid (more than one double bond)

Question 5

What is a saturated fatty acid?

Answer 5

each carbon atom is joined to the next one in the hydrocarbon chain by a single covalent bond

Question 6

what is esterification?

Answer 6

defined as the formation of ester bonds

Question 7

how is an ester bond formed?

Answer 7

through a condensation reaction

Question 8

what does an ester bond form between?

Answer 8

between the carboxyl group (-COOH) of a fatty acid and one of the hydroxyl groups of the glycerol.

Question 9

apart from the ester bond, what product is made during esterification?

Answer 9

a molecule of water

Question 10

what fatty acids make up fats?

Answer 10

saturated fatty acids because they are solid at room temperature

Question 11

what fatty acids make up oils?

Answer 11

unsaturated fatty acids because they are a liquid at room temperature

Question 12

what are the products when lipids are oxidised?

Answer 12

carbon dioxide and oxygen

drives the production of ATP

Question 13

what is a better source of energy, lipids or carbohydrates?

Answer 13

lipids, specifically triglycerides will store 3x as much energy than carbohydrates.

Question 14

define hydrophobic

Answer 14

molecules that will not dissolve in water (they don’t like water so try to get away from it)

Question 15

what are the three main characteristics of lipids?

Answer 15

• they are good insulators
• they have a low density
• they dissolve in organic solvents but are insoluble in water (so don’t interfere with water-based reactions)

Question 16

what is a phospholipid?

Answer 16

when glycerol bonds with two fatty acids and an inorganic phosphate group

Question 17

what part of the phospholipid is hydrophilic?

Answer 17

the polar phosphate head

Question 18

what part of the phospholipid is hydrophobic?

Answer 18

the lipid tails

Question 19

what happens when the phospholipid is tightly packed in water?

Answer 19

• they form a micelle (hydrophobic areas in the middle and the hydrophilic areas on the outside)
• or they form a monolayer (the hydrophilic heads in the water and the hydrophobic tails in the air)

(monolayers are rare in living cells as there is usually water-based solutions on either side)

Question 20

What happens if a monolayer of phospholipids can’t form?

Answer 20

• a bilayer is formed
• when the hydrophilic heads point to the water
• protecting the hydrophobic tails in the middle
• (known as the unit membrane)