Biological molecules

Question 1

Explain the importance of disulphide bonds in the functioning of enzymes

Answer 1

Disulphide bonds form between different parts of the polypeptide chain. Therefore this produces a specific shape for the enzyme or polypeptide. This part of the protein/ enzyme is the active site, and it allows enzyme substrate complexes to form, as complementary substrates will bind to the active site

Question 2

Test for starch

Answer 2

Add a few drops of iodine solution
A colour change from orange to blue-black indicates the presence of starch

Question 3

Test for proteins

Answer 3

Add biuret’s reagent to the solution contain proteins and shake gently
A colour change from blue to purple will indicate the presence of a protein

Question 4

Test for reducing sugars

Answer 4

Add 2cm3 of Benedict’s solution to the unknown solution.
Place in a water bath at 90-100 degrees for 5mins
A colour change from blue to brick red indicates the presence of a reducing sugar

Question 5

Test for non-reducing sugars

Answer 5

Add 1cm3 of HCl to your unknown solution
Place in a water bath at 90-100 degrees for 2minutes
Carefully neutralise the mixture with sodium hydrogen carbonate
Add 2cm3 of Benedict’s solution and place in a water bath at 90-100 degrees for 5 minutes
A colour change from blue to brick-red indicates the presence of a non reducing sugar

Question 6

Why do we use HCl in the test for non reducing sugars

Answer 6

To hydrolyse the non reducing sugar

Question 7

Test for lipids

Answer 7

Shake the unknown solution in 2cm3 of absolute ethanol for 1minute

Add 2cm3 of water and shake the mixture

A white emulsion forms