Proteins (Edexcel International A Level Biology)

People with lactose intolerance cannot digest lactose.

Lactose intolerance is due to a lack of the enzyme lactase.  

(i)

Which are the products of lactose digestion?

(1)

People with lactose intolerance can drink lactose-free milk.

Lactose-free milk is produced by treating milk with lactase.

There are two ways of removing lactose from milk:

• • Mixing a solution of lactase with the milk (free lactase)

  • Enclosing the lactase inside permeable beads and pouring the milk over them (immobilised lactase).

The diagrams show these two methods.

The table shows the effect of pH on the activity of free lactase and immobilised lactase.

Explain the effects of pH on the activity of these two enzymes.

(4)

(iii)

Suggest how the rate of activity of the lactase could be measured.

Include appropriate units in your answer.

Congenital lactose intolerance (CLI) is an extremely rare genetic disorder.

Most people with CLI are found in one country.

Suggest why most people with CLI are found in one country.

The primary structure of a protein determines its secondary structure and its three‐dimensional structure.

Complete the account by writing the most appropriate word or words on the dotted lines.

The primary structure of a protein is the specific sequence of amino acids joined together by .................................................... bonds.

These bonds are formed between the ................................................ group of one amino acid and the ..................................................... group of an adjacent amino acid by a .......................................................  reaction.

These bonds are formed during the stage of protein synthesis called ...............................................  .

The table describes the types of bond that hold the secondary and the three‐dimensional structures together.

Which type of bonding is true for each structure?