Unit 1 - Lipids

Question 1

What are the 2 groups of lipids?

Answer 1

Triglycerides and phospholipids.

Question 2

How are triglycerides formed?

Answer 2

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

Question 3

Why are triglycerides not a polymer?

Answer 3

Because it is not made of the same repeating monomers.

Question 4

Structure of a glycerol molecule?

Question 5

Structure of a fatty acid chain?

Question 6

What bond forms when a glycerol bonds with a triglyceride molecule?

Answer 6

An ester bond. So in the formation of a triglyceride molecule 3 ester bonds are produced.

Question 7

What makes lipids insoluble in water?

Answer 7

The fatty acid tails are hydrophobic which means they repel water. This means they can form insoluble droplets. The fatty acid tails face inwards shielding them from water with their glycerol heads.

Question 8

What does the letter ‘R’ represent?

Answer 8

The variable hydrocarbon chain. Shortens it as it is very long.

Question 9

What are saturated fatty acids?

Answer 9

They have single bonds between carbon atoms in the hydrocarbon chain.

Question 10

What are unsaturated fatty acids?

Answer 10

They have double bonds between the carbon atoms in the hydrocarbon chain.

Question 11

Structure of a triglyceride molecule?

Question 12

Definition of monounsaturated?

Answer 12

One double bond

Question 13

Definition of polyunsaturated?

Answer 13

More than one double bond.

Question 14

Structure of a phospholipid?

Answer 14

A glycerol molecule bonded to 2 fatty acid molecules and 1 phosphate group.

Question 15

How are phospholipids formed?

Answer 15

Condensation reactions.

Question 16

Why are phosphate heads hydrophilic?

Answer 16

Because the negative ion (phosphate group) is attracted to the slightly positive water molecules.

Question 17

Phospholipids form a what in water?

Answer 17

Bilayer.

Question 18

How many ester bonds form in a phospholipids molecule?

Answer 18

Only 2 as there are only 2 fatty acid molecules that bind to the glycerol. An ester bond DOES NOT form between the glycerol molecule and the phosphate head.

Question 19

Formation of the phospholipid bilayer?

Answer 19

The hydrophobic fatty acid tails are arranged in the middle away from the water and the hydrophilic phosphate heads are arranged on the outside in contact with the water.

Question 20

What is a bilayer used in

Answer 20

Cell surface membranes.

Question 21

Uses of triglycerides?

Answer 21

Commonly found in food and are used for energy storage.

Question 22

Uses of phospholipids?

Answer 22

They help to form the cell membranes of cells.

Question 23

How is the structure of triglycerides related to its function?

Answer 23

Long hydrocarbon fatty acid chains-contains lots of stored chemical energy-used as an energy storage molecule.
Hydrophobic fatty acid tails-insoluble in water (form insoluble droplets, with fatty acid tails in and glycerol heads out)-does not affect the water potential of cells/will not dissolve (and release whatever energy they were storing) when in contact with water.

Question 24

How is the structure of phospholipids related to its function?

Answer 24

Hydrophobic fatty acid tails and hydrophilic phosphate heads-will form a phospholipid bilayer with hydrophobic fatty acid tails pointing in away from the water and hydrophilic phosphate heads pointing towards the water-forms cell membranes. The hydrophobic fatty acid centre means that water soluble molecules cannot easily pass across the membrane.

Question 25

What’s the biological test for lipids?

Answer 25

It’s called the emulsion test. You add 2cm3 ethanol and shake (this dissolves the lipids). Then add water drop wise and shake. If lipids is present, a white emulsion will be visible ( this is fat droplets).