1.2 Lipids

Question 1

How do lipids occur in animals and plants?

Answer 1

• Animals –> fats.
• Plants –> oils.

Question 2

What elements are lipids made up of?

Answer 2

• Carbon, oxygen + hydrogen.

Question 3

Are lipids hydrophobic or hydrophillic?

Answer 3

• Hydrophobic - insoluble in water.

Question 4

What can lipids be dissolved in?

Answer 4

• Organic solvents e.g. alcohols.

Question 5

What are the two types of lipids to focus on?

Answer 5

• Triglycerides + phospholipids.

Question 6

How are triglycerides formed?

Answer 6

• Condensation reaction between glycerol (an alcohol) + 3 fatty acids.

Question 7

What types of bond are formed in a triglyceride?

Answer 7

• Ester bonds.

Question 8

What is the structure of fatty acids?

Answer 8

• Long hydrocarbon chains.
• Long hydrocarbon tail w carboxyl group at end.

Question 9

Draw a fatty acid.

Answer 9

• Zig-zag hydrocarbon.
• C=O, -OH on end.

Question 10

What is the molecular formula of glycerol?

Answer 10

• C3O3H8.

Question 11

Draw glycerol.

Answer 11

. H
|
HO – C – H
|
HO – C – H
|
HO – C – H
|
H

Question 12

What are the hydrophobic properties of triglycerides caused by?

Answer 12

• Hydrocarbon chain in fatty acid component.
• Causes them to clump together into huge globules in presence of water.

Question 13

What are the steps involved in forming triglycerides?

Answer 13

• Formation of monoglyceride - bond formed between carboxyl group (-COOH) of fatty acid + one of the hydroxide groups (-OH) of glycerol.
• Condensation reaction repeated to form diglyceride.
• Again to form triglyceride.

Question 14

Are the 3 fatty acids in triglyceride the same or different?

Answer 14

• Can be same or different.

Question 15

What is an unsaturated fatty acid?

Answer 15

• 1 or more pairs of adjacent carbon atoms in hydrocarbon chain, linked by a double covalent bond (C=C).

Question 16

What is a saturated fatty acid?

Answer 16

• One where all the bonds between carbon atoms in hydrocarbon chain are single covalent bonds (C-C).

Question 17

What are the 3 roles of lipids in organisms?

Answer 17

• Energy storage.
• Waterproofing.
• Insulation.

Question 18

Where does energy come from in lipids?

Answer 18

• Triglycerides oxidized in respiration, release energy.
• Some lost to environment some used to make ATP.

Question 19

Do lipids store more energy than carbohydrates?

Answer 19

• Yes twice as much ‘mass to mass.’
• ∴ more ‘concentrated’ energy store.

Question 20

When are fat stores common in animals?

Answer 20

• Ones that endure long unfavorable seasons in which they survive on reserves of food stored in the body.

Question 21

Where are oil stores common in plants?

Answer 21

• In seeds and fruit.
• Common to be used commercial source of edible oil for humans.

Question 22

What is the comparison between energy released on complete breakdown in lipids and carbohydrates?

Answer 22

• More in lipids than carbohydrates.

Question 23

What is the comparison between ease of breakdown in lipids and carbohydrates?

Answer 23

• Lipids not easily hydrolysed —> energy released slowly.
• Carbs more easily hydrolysed —> energy released quickly.

Question 24

What is the comparison between solubility of lipids and carbohydrates?

Answer 24

• Lipids hydrophobic ∴ do not cause osmotic water uptake by cells.
• Sugars highly soluble in water ∴ can cause osmotic water uptake by cells.

Question 25

What is the comparison between production of metabolic water in lipids and carbohydrates?

Answer 25

- Lipids - great deal of metabolic water produced on oxidation. - Carbs - less metabolic water produced on oxidation.

Question 26

What is a useful quality of lipids that helps with waterproofing?

Answer 26

- Hydrophobic ∴ they repel water.

Question 27

How does waterproofing in mammals happen?

Answer 27

- Oily secretions from sebaceous glands (found in skin). - Prevents fur + hair from becoming waterlogged when wet.

Question 28

What quality of lipids helps with insulation?

Answer 28

- Lipids are poor conductors of both heat + hydrophilic ions.

Question 29

How are triglycerides stored under the skin in mammals?

Answer 29

- As adipose tissue. - Known as subcutaneous fat.

Question 30

How does subcutaneous fat act as an insulator?

Answer 30

- Restricted blood supply ∴ little body heat distributed to fat under skin.

Question 31

What type of lipid is an insulator found in surface membranes?

Answer 31

- Myelin —> wrap around long fibers of nerve cells in animals.

Question 32

How does the lipid, myelin, act as an insulator?

Answer 32

- Many layers of myelin insulate the fibre. - Prevents passage of Na + K ions that are essential for conduction of nerve impulse. - ∴ nerve impulses travel faster than wo/ myelin.

Question 33

How do phospholipids differ in chemical structure compared to triglycerides?

Answer 33

- One of the fatty acid groups is replaced with a phosphate group.

Question 34

What happens to the phosphate groups in phospholipids?

Answer 34

- Phosphate group ionised under conditions in cells. - Phosphate group condensed w 3rd -OH group of glycerol.

Question 35

What is the 'head' of the phospholipid molecule comprised of?

Answer 35

- Glycerol attached to ionised phosphate group.

Question 36

Why does the 'head' of the phospholipid molecule have hydrophilic properties?

Answer 36

- Hydrogen bonds form readily between phosphate group + water molecules.

Question 37

What is the 'tail' of the phosphlipid molecule comprised of?

Answer 37

- 2 long fatty acid residues, comprising hydrocarbon chains.

Question 38

Is the 'tail' of the phospholipid molecule hydrophobic or hydrophilic?

Answer 38

- Hydrophobic.

Question 39

What happens when partly hydrophobic and partly hydrophilic phospholipids are placed in water?

Answer 39

- Small quantity of phospholipid in water will float w/ hydrocarbon tails exposed above the water. - Heads dissolve in water, tails stick out. - Forms single layer of phosphlipid (monolayer).

Question 40

What happens when phospholipids are mixed with water?

Answer 40

- Phospholipid molecules arrange themselves into a bilayer, w/ hydrophobic tails attracted to each other. - Hydrophilic heads in water.

Question 41

What is a bilayer?

Answer 41

- Single structure made of 2 layers of molecules, usually used to describe arrangement of phospholipids in cell membrane.