Lipids

Question 1

What are lipids?

Answer 1

Usually known as fats and oils.

Question 2

Why do lipids differ from carbohydrates?

Answer 2

They are not polymers formed from monomers (repeating units). They are made from a variety of different components.

Question 3

Name a component found in all lipids.

Answer 3

Hydrocarbons (molecules that contain carbon and hydrogen only).

Question 4

Name two types of lipids.

Answer 4

Triglycerides and phospholipids.

Question 5

What is meant by hydrophobic?

Answer 5

Repels water.

Question 6

How many fatty acids are in one triglyceride?

Answer 6

3

Question 7

How many molecules are in a triglyceride? How are they bonded?

Answer 7

There are 4: 3 fatty acids and 1 glycerol. They are bonded by ester bonds formed in a condensation reaction.

Question 8

What makes triglycerides insoluble in water?

Answer 8

Fatty acids have long tails made of hydrocarbons. They hydrocarbons are hydrophobic and repel water. Hence these tails make triglycerides insoluble in water.

Question 9

What is meant by hydrophilic?

Answer 9

Attracts water

Question 10

Name two categories of fatty acids.

Answer 10

Saturated and unsaturated.

Question 11

Describe the structure of a saturated fatty acid.

Answer 11

Fatty acid: RCOOH
R group contains only single C-C bonds

Question 12

Describe the structure of an unsaturated fatty acid.

Answer 12

Fatty acid: RCOOH
R group contains one/more double C=C bonds

Question 13

How are triglycerides formed?

Answer 13

A molecule of glycerol and 3 fatty acids are chemically joined by 3 ester bonds in a condensation reaction producing a triglyceride and 3x H2O

Question 14

What are the lipids found in a cell membrane called?

Answer 14

Phospholipid bilayer

Question 15

How many molecules are found in a phospholipid?

Answer 15

There are 4: 2 fatty acids, 1 glycerol and 1 phosphate group

Question 16

Which part of a phospholipid is hydrophobic?

Answer 16

The fatty acid chains

Question 17

Which part of a phospholipid is hydrophilic?

Answer 17

The phosphate head

Question 18

What is the difference between triglycerides and phospholipids?

Answer 18

Triglycerides contain 3 fatty acids and phospholipids contain 2 fatty acids. Phospholipids contain a phosphate group and triglycerides don’t.

Question 19

What are some similarities between phospholipids and triglycerides?

Answer 19

They’re both lipids.
They both contain glycerol.
They both contain hydrophobic features.

Question 20

What are triglycerides used for?

Answer 20

Used as energy storage molecules

Question 21

What is a benefit of triglycerides being insoluble?

Answer 21

Water unable to pass through and thus doesn’t take up space that can be used for energy.

Question 22

How are triglyceride structures related to their properties?

Answer 22

High ratio of energy storing C-H bonds to C-C bonds; excellent energy store.
Low mass to energy ratio; good for storage as lots of energy can be stored in a small volume.
They’re non-polar and insoluble in water; their storage does not affect the water potential of cells.
High ratio of O-H bonds means that triglycerides release water when oxidised; provides water for organisms to live in dry environments.

Question 23

How are phospholipid structures related to their properties?

Answer 23

Polar in aqueous environment; bilayer can be formed.
Hydrophilic heads; used to hold at the surface of the cell surface membrane.
Structure allows them to form glycolipids with carbohydrates; important on cell surface membrane for cell recognition.

Question 24

What is the test for lipids?

Answer 24

The emulsion test

Question 25

How do you test for lipids?

Answer 25

Add sample to grease-free test tube.
Add ethanol and shake.
Milky, white emulsion formed if lipid is present