Biological molecules - PROTEINS

Question 1

What are the monomers that make up proteins?

Answer 1

Amino acids - hence proteins are polymers of amino acids

Question 2

What are anabolic reactions?

Answer 2

Anabolic reactions make polymers; for example - condensation reactions join two molecules together with the formation of a chemical bond and involves the formation of a water molecule.

Question 3

What are catabolic reactions?

Answer 3

Catabolic reactions reverse condensation reactions; for example - hydrolysis reactions break a chemical bond between two molecules and involves the use of a water molecule.

Question 4

What is the primary structure of the proteins?

Answer 4

The amino acid sequence

Question 5

Describe the structure of an amino acid

Answer 5

Amino group (NH2) + variable group (R) + carboxyl group (COOH)

Question 6

Why are amino acids described as amphoteric?

Answer 6

They can act as a base or an acid

Question 7

How many naturally occurring amino acids are there?

Answer 7

20

Question 8

What are the products of a condensation reaction between two amino acids?

Answer 8

A peptide bond, a H2O molecule, and a new dipeptide

Question 9

Why is the primary structure of a protein important?

Answer 9

The sequence of amino acids determines its (the protein’s) properties and shape.

Question 10

What is the secondary structure of proteins?

Answer 10

The secondary structure is the shape which the polypeptide chain forms as a results of hydrogen bonding. This is most often a spiral known as the α-helix, although other configurations occur.

Question 11

What is an α-helix?

Answer 11

Hydrogen bonds can form an α-helix. This is a tight coil of amino acids held together by the hydrogen bonds.

Question 12

What is a β- pleated sheet?

Answer 12

Polypeptide chains can also form β- pleated sheets by joining with hydrogen bonds

Question 13

What type of peptidase will hydrolyse the bond between a dipeptide?

Answer 13

Dipeptidase

Question 14

Describe a biochemical test to confirm the presence of protein in a solution

Answer 14

Add biuret’s solution to a liquid food sample; if proteins are present, the colour will change from blue-lilac

Question 15

Describe 3 ways in which all dipeptides are similar

Answer 15

• All dipeptides consist of two amino acids joined
• All dipeptides will have peptide bonds
• All dipeptides will have amine and dicarboxylic acid groups

Question 16

Describe one way in which dipeptides will differ from each other

Answer 16

They will have different ‘R’ groups

Question 17

What is the tertiary structure of a protein?

Answer 17

The tertiary structure of a protein is when the secondary structures (α-helices and β- pleated sheets) fold up to form a very precise three dimensional structure.

Question 18

What are London forces?

Answer 18

• London forces are very weak, temporary forces of attraction between some non-polar ‘R’ groups.
• London forces can be split by high temperatures.

Question 19

What are disulphide bonds?

Answer 19

• Some ‘R’ groups contain sulphur; If 2 ‘R’ groups contain sulphur, they form covalent (disulphide) bonds.
• Disulphide bonds are very strong, and can resist high temperatures.

Question 20

Why do polypeptides fold?

Answer 20

As only some ‘R’ groups are attracted to each other, the repulsion means the chain folds into a specific shape.

Question 21

What happens to the bonds in the polypeptide if heated?

Answer 21

If heated, the London forces and the hydrogen bonds are more likely to break, denaturing the protein.

Question 22

What are globular proteins?

Answer 22

Globular proteins, often enzymes, form a spherical mass with a specific 3D shape
Eg. haemoglobin

Question 23

What are hydrophilic and hydrophobic groups? (in an aqueous solution)

Answer 23

• Hydrophilic groups dissolve in water (they are attracted by the hydrogen bonds of water, thus they are on the outside of the molecule)
• Hydrophobic groups repel water

Question 24

What happens to globular proteins if they are taken out of water?

Answer 24

If taken out of water, the protein will unravel and change shape, as the hydrophilic groups no longer have access to water.

Question 25

What is the quaternary structure of a protein?

Answer 25

Some proteins consist of more than one polypeptide chain held together

Question 26

What are prosthetic groups?

Answer 26

Prosthetic groups are non organic, meaning they contain metal ions, sugars, vitamins, methyl groups, phosphate groups etc.

Question 27

Describe haemoglobin

Answer 27

• Haemoglobin contains iron, and consists of 4 polypeptide chains - 2 β-subunits and 2 α- subunits.
• Haemoglobin contains 4 haem prosthetic groups

Question 28

What are fibrous proteins?

Answer 28

• Fibrous protein molecules form long chains or fibres (they have primary, secondary, tertiary and quaternary structure)
• The fibres form a triple helix of polypeptide chains, held together by hydrogen bonds

Question 29

How does the structure of fibrous proteins support its function, and where could we find them?

Answer 29

• The fibrous nature makes these proteins insoluble in water, which makes them useful for structure and support.
• Eg. Collagen; found in skin, teeth, bones, tendons, blood vessel walls

Question 30

Why are collagen fibres so strong?

Answer 30

Collagen fibres are very strong as they have the combined strength of the individual fibrils