Lesson 8/9 - Lipids - Triglycerides/phospholipids

Question 1

Lipids all share these characteristics:

Answer 1

● All contain the elements Carbon, Hydrogen and Oxygen
● They are non-polar molecules due to the large number of C’s & H’s and so are insoluble in water
● They are soluble in other organic solvents (eg. alcohols)

Question 2

What are the 2 main groups of lipids?

Answer 2

● Triglycerides (the fats and oils) - a component of our diet
● Phospholipids - a component of cell membranes

Question 3

How are triglycerides formed?

Answer 3

By the condensation of 1 molecule of glycerol and 3 molecules of fatty acid.

Question 4

Which bond is created when glycerol bonds to a fatty acid (RCOOH) ?

Answer 4

Ester bond

Question 5

Which group of a fatty acid can be saturated or unsaturated?

Answer 5

R group

Question 6

What’s the difference between a triglyceride and a phospholipid?

Answer 6

In a phospholipid, 1 of the fatty acid’s of a triglyceride is substituted with a phosphate containing group.

Question 7

What’s a fatty acid?

Answer 7

● Long hydrocarbon chain with a carboxylic acid group at one
end
● Some fatty acids contain carbon double bonds and some don’t

Question 8

What’s the emulsion test for lipids?

Answer 8

1. Mix the sample being tested with alcohol (eg. ethanol) in a test tube
2. Shake the tube thoroughly
3. Add cold water and shake gently
4. If a milky-white emulsion is formed, this indicates the presence of a lipid

Question 9

Whats the Difference between saturated and unsaturated fatty acids?

Answer 9

● Saturated fatty acids have only C-C so form linear hydrocarbon chains.
● Unsaturated fatty acids have one or more C=C which causes the hydrocarbon chain to bend.

Question 10

Saturated definition

Answer 10

No double bonds between carbon atoms.

Question 11

Mono-unsaturated definition

Answer 11

Contains 1 double bond between carbon atoms.

Question 12

Polyunsaturated definition

Answer 12

More than 1 double bond between carbon atoms.

Question 13

Patterns/formation of saturated and unsaturated fatty acids

Answer 13

● Saturated fatty acids fit closely together in a regular pattern.
● Unsaturated fatty acids push each other apart forming irregular patterns.

Question 14

Properties of saturated fatty acids

Answer 14

● Contain only C-C bonds (and therefore form linear hydrocarbon chains)
● Fatty acids can pack closely together
● Strong attractions (intermolecular bonds) between fatty acid chains
● High melting points
● Solids at room temperature

Question 15

Properties of unsaturated fatty acids

Answer 15

● Contain one or more C=C (causing the hydrocarbon chains to bend)
● The nonlinear chains do not allow the fatty acid molecules to pack closely together
● Weaker attractions (intermolecular bonds) between fatty acid chains
● Lower melting points
● Liquids at room temperature

Question 16

Why are fats generally solid at room temperature?

Answer 16

Fats are generally made of saturated fatty acids hence why they are solid at room temperature.

Question 17

Why are oils generally liquid at room temperature?

Answer 17

Oils are generally made of unsaturated fatty acids hence why they are liquid at room temperature.

Question 18

Which term describes triglycerides being large, insoluble molecules?

Answer 18

Hydrophobic

Question 19

What happens during condensation? (triglyceride)

Answer 19

● Produces a triglyceride
● Formed from a glycerol and 3 fatty acids
● 3 water molecules are released
● 3 ester bonds formed

Question 20

What happens during hydrolysis? (triglyceride)

Answer 20

● Triglyceride is split by the addition of 3 water molecules
● 3 ester bonds broken
● Glycerol and 3 fatty acids are formed

Question 21

Which intermolecular bonds in saturated and unsaturated fatty acids are stronger?

Answer 21

The intermolecular bonds between the saturated fatty acids are stronger than the ones between the unsaturated bonds, as they closer together.

Question 22

Which part of a phospholipid is hydrophobic (repels water) and which is hydrophilic (attracts water) ?

Answer 22

hydrophobic (repels water) - fatty acid
hydrophilic (attracts water) - phosphate molecule

Question 23

Which fatty acids does a phospholipid contain?

Answer 23

A saturated and an unsaturated fatty acid

Question 24

How do phospholipids position themselves when placed in water?

Answer 24

So that the heads are as close to water as possible and the tails are as far from water as possible.

Question 25

What are some roles of lipids?

Answer 25

● Lipids are a source of energy - provide more than double the energy as the same amount of carbohydrate
● Waterproofing (as they are hydrophobic) - waxy, lipid cuticles are found in both plants and insects to conserve water (reduce water loss)
● Insulation - fats are slow conductors of heat, so, a layer of fat stored under the skin helps to retain body heat (prevent it being lost)
● Protection - fat is often stored round delicate organs eg. the kidney, to protect from damage
● Buoyancy - slightly less dense than water
● Electrical insulator - surrounds nerves to increase the speed of electrical impulses