3.5 Lipids

Question 1

What are lipids?

Answer 1

Non-polar macromolecules containing the elements carbon, hydrogen and oxygen. Commonly known as fats and oils.

Question 2

Why are lipids not soluble?

Answer 2

There are no positive and negative areas within the lipid molecules as they are non-polar. This means that the electrons in the outer orbitals that form the bonds are more evenly distributed than in polar lipid molecules.

Question 3

What are macromolecules?

Answer 3

Large complex molecules with a large molecular weight.

Question 4

What is a triglyceride?

Answer 4

A lipid composed of one glycerol molecule and three fatty acids.

Question 5

What elements make up a triglyceride molecule?

Answer 5

• Carbon (C)
• Hydrogen (H)
• Oxygen (O)

Question 6

What is glycerol?

Answer 6

An alcohol found in triglycerides.

Question 7

What are fatty acids?

Answer 7

Long chains of carboxylic acids used in the formation of triglycerides.

Question 8

What functional group is found in both glycerol and fatty acids?

Answer 8

Hydroxyl group (OH)

Question 9

How are triglycerides formed?

Answer 9

Hydroxyl groups interact on the glycerol molecule and fatty acids producing three water molecules.

Question 10

What type of bonds form between a glycerol molecule and three fatty acids? and what type of reaction is this?

Answer 10

Ester bonds formed in an esterification reaction, a type of condensation reaction.

Question 11

Why are triglycerides also an example of a hydrolysis reaction?

Answer 11

Three water molecules are needed to be supplied to break down the triglyceride molecule into one glycerol molecule and three fatty acids.

Question 12

What are saturated triglycerides?

Answer 12

Fatty acid chains that have no double bonds present between the carbon atoms .

Question 13

What are unsaturated tryiglycerides?

Answer 13

Fatty acid chains that have double bonds present between the carbon atoms.

Question 14

What is meant by a monosaturated triglyceride?

Answer 14

If the fatty acid chain contains one double bond between its carbon atoms.

Question 15

What is meant by a polyunsaturated triglyceride?

Answer 15

If the fatty acid chain contains two or more double bonds between its carbon atoms.

Question 16

Why are saturated triglycerides described as oils rather than fats?

Answer 16

The presence of double bonds causes the molecule to kink or bend and they therefore cannot pack so closely together. This makes them a liquid at room temperature rather than a solid.

Question 17

What are phosopholipids?

Answer 17

Modified triglycerides, where one fatty acid has been replaced with a phosphate group.

Question 18

What elements make up a phospholipid molecule?

Answer 18

• Carbon (C)
• Hydrogen (H)
• Oxygen (O)
• Phosphorus (P)

Question 19

Why are the inorganic phosphate ions soluble in water?

Answer 19

Phosphate ions have extra electrons and so are negatively charged.

Question 20

What is meant by being hydrophobic?

Answer 20

The physical property of a molecule that is repelled by water.

Question 21

What is meant by being hydrophilic?

Answer 21

The physical property of a molecule that is attracted to water.

Question 22

Which areas of phospholipids are hydrophobic and hydrophilic?

Answer 22

Non-polar ends (fatty acid chains) is hydrophobic and the charged head (phosphate ion) is hydrophilic.

Question 23

Why are phospholipids called surface active agents or surfactants?

Answer 23

They form a layer on the surface of the water with the phosphate heads in the water and the fatty acid tails sticking out of the water. (like oil bubbles in water)

Question 24

Why do phospholipids play a key role in the formation of cell membranes?

Answer 24

They are able to separate the external aqueous environment from the aqueous cytosol within cells.

Question 25

What are sterols?

Answer 25

Another type of lipid found in cells, also know as steroid alcohols.

Question 26

What is the structure of sterols?

Answer 26

Four carbon ring structure with a hydroxyl (OH) group at one end.

Question 27

What areas of sterols are hydrophobic and hydrophilic?

Answer 27

The hydroxyl (OH) group is polar and therefore hydrophilic and the rest of the molecule is hydrophobic.

Question 28

What are cholesterols?

Answer 28

A sterol.

Question 29

Where does the body manufacture cholesterols?

Answer 29

Liver and Intestines.

Question 30

Why are cholesterols important in the formation of cell membranes?

Answer 30

They are positioned between phospholipids with their hydroxyl (OH) at the periphery of the membrane. This adds stability to the cell membranes and regulates fluidity but keeping membranes fluid at low temperatures and stopping them from becoming too fluid at high temperatures.

Question 31

Give some examples of molecules manufactured by using cholesterols?

Answer 31

• Vitamin D
• Steroid hormones
• Bile

Question 32

What are some biological roles of lipids?

Answer 32

• Membrane formation and the creation of hydrophobic barriers.
• Hormone production.
• Electrical insulation necessary for impulse transmission.
• Waterproofing, eg. bird feathers and plant leaves.

Question 33

What are some important long-term energy storage roles of lipids, triglycerides in particular?

Answer 33

• Thermal insulation to reduce heat loss
• Cushioning to protect vital organs.
• Buoyancy for aquatic animals.

Question 34

What test is used to identify lipids?

Answer 34

Emulsion test.

Question 35

What is the emulsion test?

Answer 35

A laboratory test for lipids using ethanol.

Question 36

How is a test for lipids carried out?

Answer 36

The sample is mixed with ethanol and the resulting solution is mixed with water and shaken.

Question 37

What is seen in a positive test for lipids?

Answer 37

A white emulsion forms as a layer on top of the solution.

Question 38

What is seen an a negative test for lipids?

Answer 38

The solution remains clear.

Question 39

What is food synergy?

Answer 39

The combined effect of a whole range of nutrients on a human’s health.