Biological Molecules - Lipids

Question 1

What characteristics do lipids share?

Answer 1

• They contain carbon, hydrogen and oxygen.
• The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates.
• They are insoluble in water.
• They are soluble in organic solvents such as alcohols and acetone.

Question 2

What is the main role of lipids?

Answer 2

Cell membranes - phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across.

Question 3

What are the other roles of lipids?

Answer 3

Source of energy - when oxidised they provide energy.
Waterproof - they are insoluble in water and therefore useful in waterproofing.
Insulation - fats are slow conductors of heat and when stored beneath the body surface help to retain body heat.
Protection - fat is often stored around delicate organs.

Question 4

What are triglycerides?

Answer 4

They have 3 fatty acids combined with a glycerol molecule. Each fatty acid forms an ester bond with glycerol in a condensation reaction. Hydrolysis of a triglyceride therefore produces glycerol and three fatty acids.

Question 5

What are triglycerides made up of?

Answer 5

One glycerol and three fat acids joined by ester bonds formed in condensation reactions.

Question 6

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

Answer 6

Saturated fatty acids don’t contain any carbon double bonds in the chain.

Unsaturated fatty acids contain one or more carbon bonds. This means the presence of the double bond enables the molecule to bend as a result.

Question 7

Give four things about triglycerides structures that relates to their properties.

Answer 7

– High ratio of energy storing carbon – hydrogen bond to carbon atom and therefore they are excellent energy stores.
– a low mass to energy ratio meaning that they are a good storage molecule with a lot of energy being stored in a small volume this is beneficial for animals as it is less mass to move around.
– Being large and nonpolar lipids are insoluble in water and therefore storage does not affect the water potential of cells.
– A high ratio of hydrogen – oxygen atoms means that the triglycerides release water when they are oxidised and therefore provide an important source of water for organisms to live in dry environments .

Question 8

What are phospholipids made up of?

Answer 8

The glycerol, backbone, two fatty acids and a phosphate containing group.

Question 9

What is meant by a nonpolar or polar molecule?

Answer 9

Polar molecules have an uneven distribution of charge across their geometry, resulting in one side being positive and the other side being negative.

Question 10

What is the main property of a phospholipid and why?

Answer 10

It is a polar molecule because it has a hydrophilic head and a hydrophobic tail.

Question 11

Relate phospholipid structure to their properties

Answer 11

– In an acquiesce environment being polar means they can form a phospholipid bilayer.
– The hydrophilic heads of the phospholipids can be used to at the surface of the cell surface membrane.
– Their structure allows them to form glycol lipids with carbohydrates which are important on the cell surface membrane for cell recognition.

Question 12

How do you do the emulsion test for the presence of lipids?

Answer 12

1. Take a completely grease free test tube and add 2 cm³ of the sample to be tested and add 5 cm³ of ethanol.
2. add 5 cm³ of water and shake.
3. A cloudy white colour indicates the presence of lipids.

Question 13

What are the monomers of polypeptides?

Answer 13

Amino acids.

Question 14

What is the structure of an amino acid?

Answer 14

They contain one amine group (NH2) a carboxylic acid group (-COOH) and a variable group which is a carbon containing chain.

Question 15

How many different amino acids are there and what are the differences determined by?

Answer 15

There are 20 different amino acids each determined by the different R groups.

Question 16

What is the primary structure of a protein?

Answer 16

The order and number of amino acids in a protein this primary structure contains the initial sequence of amino acids and will therefore determine the proteins function in the end.

Question 17

What is the secondary structure of proteins?

Answer 17

Is the shape that the chain of amino acids make either an alpha helix or a beta pleated sheet. The hydrogen in the -NH has a slight positive charge while the oxygen in the -C=O has a slight negative charge as a result weak hydrogen bonds can form leading to alpha helices or beta pleated sheets.

Question 18

What is the tertiary structure of proteins?

Answer 18

The 3-D shape of the protein is then formed from further twisting and folding a number of different bonds maintain the structure.
Disulphide bridges: interactions between the sulphur in the R group of the amino acid cysteine these are strong and not easily broken.
Ionic bonds: form between the carboxyl and amine groups that are not involved in the peptide bond they are easily broken by pH and are weaker than disulphide bridges.
Hydrogen bonds: numerous and easily broken.

Question 19

What is meant by a globular protein?

Answer 19

They are compact.

Question 20

What is a fibrous protein?

Answer 20

Long and thus can be used to form fibres.