Lipids (page 24 - 25)

Question 1

You need to learn about three types of Lipids, name them?

Answer 1

Triglycerides
Phospholipids
Cholesterol

Question 2

What are Triglycerides?

Answer 2

Triglycerides are a kind of lipid.

they are macromolecules.

Question 3

What are macromolecules?

Answer 3

they are complex molecules with a relatively large molecular mass. (triglycerides are macromolecules).

Question 4

What chemical elements do Triglycerides contain?

Answer 4

like all lipids, they contain the chemical elements
carbon, hydrogen and oxygen.

Question 5

What molecules do Triglycerides have?

Answer 5

they have one molecules of glycerol with three fatty acids attached to it. (see diagram 1 on page 24)

Question 6

Explain the structure of a Triglyceride fatty acids?

Answer 6

fatty acid molecules have long ‘tails’ made of hydrocarbons (compounds that contain only carbon and hydrogen atoms).

The tails are hydrophobic (they repel water molecules). These tails make lipids insoluble in water. All fatty acids have the same basic structure but the hydrocarbon tail varies. (see diagram 1 on page 24). - Variable ‘R’ group hydrocarbon tail.

Question 7

What do Tyiglycerides contain?

Answer 7

they contain Ester Bonds

Question 8

Triglycerides are synthesised by the formation of an ester bond between what?

Answer 8

between each fatty acid and the glycerol molecule. (see diagram 2 on page 24).

Question 9

Each ester bond is formed by what reaction?

Answer 9

ester bond is formed by a condensation reaction (in which a water molecule is released).

Question 10

What is the process called in which triglycerides are synthesised?

Answer 10

esterification.

Question 11

When do Triglycerides break down?

Answer 11

when the ester bonds are broken. Each ester bond is broken in a hydrolysis reaction (in which a water molecule is used up).

Question 12

There are two kinds of fatty acids, name them? and how do you know the difference?

Answer 12

saturated and unsaturated.

The difference is their hydrocarbon tails.

Question 13

How many double bonds do saturated fatty acids have between their carbon atoms?

Answer 13

saturated fatty acids dont have any double bonds between their carbon atoms. The fatty acid is ‘saturated’ with hydrogen.

see diagram 3 on page 24 at the saturated hydrocarbon chain.

Question 14

What is the general formula for a saturated fatty acid?

Answer 14

CnH(2n + 1)COOH

Question 15

How many double bonds do unsaturated fatty acids have between their carbon atoms, and explain what happens to the chain?

Answer 15

Unsaturated fatty acids have at least ONE double bond between carbon atoms, which causes the chain to kink.

look at diagram 4 on page 24 of the unsaturated hydrobarbon chain.

Question 16

What are Phospholipids?

Answer 16

Phospholipids are also macromolecules. they are similar to triglycerides expect one of the fatty acid molecules is replaced by a phosphate group. (see diagram 5 on page 24 of the phospholipid structure)

Question 17

The Phosphate group is Hydrophillic, what do this mean?

Answer 17

it attracts water molecules and the fatty acid tails are hydrophobic.

Question 18

You need to know how the properties of triglycerides, phospholipids and cholesterol are related to their functions.

In animals and plants, triglycerides are mainly used as what?

Answer 18

energy storage molecules.

Question 19

Some bacteria (e.g. Mycobacterium tuberculosis) use tryglycerides to store both energy and carbon. Why are Triglycerides good for storage?

Answer 19

1) The long hydrocarbon tails of the fatty acids contain lots of chemical energy - a load of energy is released when they’re broken down. Because of these tails, lipids contain about twice as much energy per gram as carbohydrates.

2) They’re insoluble, so they don’t cause water to enter the cells by osmosis (see page 58) which would make them swell. The triglycerides bundle together as insoluble droplets in cells because the fatty acid tails are hydrophobic (water repelling) - the tails face inwards, shielding themselves away from water with their glycerol heads. (see diagram 1 on page 25)

Question 20

Where are Phospholipids found?

Answer 20

in the cell membranes of all eukaryotes and prokaryotes.

They make up wha’t known as the phosphholipid bilayer.

Question 21

Regarding Phospholipids, cell membranes control what enters and leaves a cell, explain how?

Answer 21

1) Phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side (see diagram 2 on page 25).

2) The centre of the bilayer is hydrophobic, so water-soluble substances can’t easily pass through it - the membrane acts as a barrier to those substances.

Question 22

Explain the structure of the Cholesterol?

Answer 22

Cholesterol is another type of lipid - it has a hydrocarbon ring structure attached to a hydrocarbon tail. The ring structure has a polar hydroxl (OH) group attached to it.

Question 23

In eukaryotic cells, cholesterol molecules help strengthen the cell membrane, how?

Answer 23

by interacting with the phospholipid bilayer.

1) Cholesterol has a small size and flattened shape - this allows cholesterol to fit in between the phospholipid molecules in the membrane (see diagram 3 on page 25).

2) They bind to the hydrophobic tails of the phospholipids, causing them to pack more cloesly together. This helps to make the membrane less fulid and more rigid.

Question 24

What do ‘polar’ mean?

Answer 24

it means it has a slightly negatively charged bit and a slightly positely charged bit. (see page 20).

Question 25

What are triglycerides composed of?

Answer 25

triglycerides are a type of lipid that is commonly known as fat. The triglyceride structure is compsed of three fatty acids attached to a glycerol backbone.

Tryglycerides are a major form of energy storage in animals and are also used for insulation and protection of organs.

they are macromolecules. they contain the chemical elements carbon, hydrogen and oxygen. triglycerides have one molecule of glycerol with three fatty acids attached to it.

Question 26

What is the difference between a saturated fatty acid and an unsaturated fatty acid?

Answer 26

Saturated fatty acids have hydrocarbon chains connected by single bonds only.

unsaturated fatty acids have one or more double bonds.

Question 27

Sketch the structure of a phospholipid?

Answer 27

see diagram on page 24

Question 28

Explain how phospholipid molecules arrange themselves in cell membranes and relate this to their structure (3 marks)?

Answer 28

They arrange themselves into a phospholipid bilayer/double layer (1 mark), with fatty acid tails facing towards each other (1 mark). This is because the fatty acid tails are hydrophobic (water-repelling), forcing them to face inwards, away from the water on either side of the membrand (1 mark).

Question 29

Explain how each of these features of lipids is important for their function in living things:

a) Cholesterolmolecules have a flattened shape (2 marks)
b) Triglycerides have a hydrophobic tail (2 marks).

Answer 29

a) the flattened shape allows the cholesterol molecules to fit inbetween the phospholipids, casing the phospholipids to pack together more tightly (1 mark), which makes the membrane less fulid andmore rigid (1 mark)

b) the hydrophobic tails force triglycerides to clump together in the cytoplasm as insoluble droplets (1 mark). This means they can be stored in cells without affecting the cell’s water potential (1 mark).