2.1.2 - Biologial Molecules (set C - Lipids)

Question 1

What are lipids?

Answer 1

Commonly known as fats and oils - they are large complex molecules (macromolecules) containing the elements carbon,hydrogen and oxygen, they are non soluble in water due to the fact they are non-polar

Question 2

Explain why lipids are non soluble in water?

Answer 2

Lipids are a non-polar molecule which means the electrons in the bonds are more evenly distributed so there are no negative or positive regions - and therefore aren’t soluble in water

• explains why oil does not mix with water

Question 3

What is the state of lipids at room temperature?

Answer 3

Fats are solid at room temperature where as oils are liquid

Question 4

What are triglycerides?

Answer 4

Type of fat made by combining one glycerol molecule with three fatty acids through the process of esterification

• fatty acid is part of the carboxylic acid (COOH)
• glycerol is part of the alcohol group (OH)

Question 5

Explain what happens during the synthesis of triglycerides?

Answer 5

When one glycerol molecule (OH) combines with three fatty acids (COOH) the hydroxyl groups interact (OH) which leads to the formation of three water molecules and ester bonds between the fatty acids and glycerol molecule

• this is a condensation reaction

Question 6

What is esterification?

Answer 6

Example of a condensation reaction and is a result of a carboxylic acid (COOH) reacting with an alcohol (OH) which forms an ester and water

-example is the synthesis of triglycerides where ester bonds are formed between glycerol molecules and the three fatty acids acids

Question 7

What happens when triglycerides are broken down?what type of reaction is it?

Answer 7

Hydrolysis reaction - requires three water molecules to be supplied to reverse the reaction that formed the triglyceride

Question 8

Explain what a saturated fatty acid is?

Answer 8

Fatty acid chain which has no double bond present between carbon atoms, because all the carbon atoms form the maximum number of bonds with hydrogen atoms

Question 9

Explain what a unsaturated fatty acid is?

Answer 9

Fatty acid which has some double bonds present between carbon atoms, this results in them being liquid at room temperature

Question 10

Explain why unsaturated fatty acids are liquid at room temperature?

Answer 10

Presence of double bonds causes the molecule to kink or bend which prevents it from packing closely together - results in it being liquid at room temperature

Question 11

What does it mean if the fatty acid is monounsaturated?

Answer 11

That the fatty acid has just one double bond

Question 12

What does it mean if the fatty acid is polyunsaturated?

Answer 12

That there are two or more double bonds present

Question 13

Explain what phospholipids are?List the elements they contain?

Answer 13

Modified triglycerides which contain the elements phosphorus,carbon,hydrogen and oxygen

• have a hydrophilic head and a hydrophobic tail

Question 14

What makes a lipid a phospholipid?

Answer 14

one of the fatty acid chains in a triglyceride molecule is replaced with a phosphate group, this makes it a phopsoplipid

Question 15

Explain the 3 features of phospholipids?

Answer 15

• due to their length they have a non-polar tail and a charged head (phosphate group)
• have hydrophobic tails
• have hydrophilic heads

Question 16

Explain why the heads of phospholipids are hydrophilic?

Answer 16

Phosphate ions in the head of the phospholipid have extra electrons which makes them negatively charged and soluble in water

• hydrophilic - interact and are attracted to water

Question 17

Explain how phospholipids interact with water?

Answer 17

They form a layer on the surface of the water with the the phosphate heads in the water and fatty acid tails sticking out of the water

• due to this their called surfactants

Question 18

Explain how phospholipids form a bilayer?

Answer 18

Form a two-layered sheet (bilayer) with all the hydrophobic tails pointing towards the centre of the sheet protected from the water by the hydrophilic heads

Question 19

Why are phospholipid bilayers important for cells?

Answer 19

Phospholipid bilayer is involved in cell membranes, as they are able to separate an aqueous environment in which the cells exist from the aqueous cytosol within the cell

Question 20

What are sterols?

Answer 20

Sterols are another type of lipid found in cells, they are not fats or oils - they are complex alcohol molecules with OH groups - have dual hydrophilic/hydrophobic characetristics

• example of sterol is cholesterol

Question 21

What is cholesterol?

Answer 21

Sterol manufactured primarily in the liver and intestines, helps to regulate the fluidity of the cell membrane

• vitamin D and bile are manufactured using cholesterol

Question 22

Explain how cholesterol regulates the fluidity of the cell?

Answer 22

Interacts with the phospholipid bilayer which keeps the membrane fluid at low temperatures and stops them become too fluid at high temperatures

Question 23

Explain how cholesterol prevents the membrane becoming too fluid at high temperatures?

Answer 23

binds to hydrophobic tails of phospholipids, which causes them to be more tightly packed together which makes the membrane less fluid and more rigid

Question 24

Explain how cholesterol prevents the membrane becoming too rigid at low temperatures?

Answer 24

prevents phospholipids from packing too close together, so increases membranes fluidity

Question 25

Explain a key adaption that allows cholesterol to perform its job?

Answer 25

Small size and flattened shape, allows cholesterol to fit in between the phospholipid molecules in the membrane

Question 26

Define hydrophobic?

Answer 26

Insoluble in water, so they repel water

Question 27

Define hydrophilic?

Answer 27

Able to interact with water through hydrogen bonding

Question 28

Give three roles of lipids?

Answer 28

• membrane formation and creation of hydrophobic barriers
• hormone production
• electrical stimulation necessary for impulse transmission

Question 29

Give three role of triglycerides?

Answer 29

• thermal insulation - to reduce heat loss
• cushioning to protect vital organs
• buoyancy for aquaitc animals

Question 30

Explain how lipids can be identified?

Answer 30

Emulsion test - sample is mixed with ethanol and the solution is then mixed with water and shaken - results indicate wether their is a presence of lipid

Question 31

Explain what the results from the emulation test show?

Answer 31

• white emulsion layer on top of the solution - indicates presence of lipid
• if it remains clear it is negative - no lipid present

Question 32

Relate the structure of triglycerides to their functions - give 3?

Answer 32

• slow conductor of heat - thermal insulation
• insoluble hydrocarbon chain which means there is no effect on water potential of cell - used for waterproofing
• less dense than water - buoyancy of aquatic animals

Question 33

Describe the structure and function of cholesterol?

Answer 33

Steroid structure of 4 hydrocarbon rings - hydrocarbon tail on one side, hydroxyl group (-OH) on the other side

• adds stability to cell surface phospholipid bilayer by connecting molecules and reducing fluidity

Question 34

Describe the structure and function of phospholipids?

Answer 34

Glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head

• forms phospholipid bilayer in water - component of membranes
• tails can splay outwards - waterproofing