3.1.4 Proteins

Question 1

Describe what is meant by a protein

Answer 1

• Proteins are polymers as they are made up of many monomers called
  amino acids. The sequence, type, and number of amino acids within a
  protein are important as they determine the shape and therefore the
  function.

Question 2

Describe the structure of an amino acid

Answer 2

• Amino group (-NH2)
• Carboxyl group (-COOH)
• A hydrogen atom
• R-group (variable side chain, which is how amino acids differ)

Question 3

Describe the formation of a dipeptide from 2 amino acids

Answer 3

• Amino acids react together in a condensation reaction, where peptide bonds form between them. Water is removed

Question 4

Describe the primary structure of proteins

Answer 4

• The sequence, type, and number of amino acids within a protein are important as they determine the shape and therefore the function. Peptide bonds form between amino acids

Question 5

Describe the secondary structure of proteins

Answer 5

• The folding of polypeptide chain due to hydrogen bonding
• Form alpha-helix or Beta-pleated sheet

Question 6

Describe the tertiary structure of proteins

Answer 6

• 3D highly specific complex shape formed by interactions between R-groups:
• Hydrogen bonds (between R-groups)
• Ionic bonds (between oppositely charged R-groups)
• Disulphide bridges (between cysteine amino acids)
• Weak hydrophobic interactions (between non-polar R-groups)

Question 7

Describe the quaternary structure of proteins

Answer 7

• Multiple polypeptide chains

Question 8

Explain the relationship between the primary structure and the tertiary structure of proteins

Answer 8

• The sequence, type and position of amino acids in the primary structure determines what types of bonds are able to form, and the position of these bonds, in the teritary structure, which therefore determines the final shape of the proteins.

Question 9

Describe how to test for the presence of protein

Answer 9

• Add biuret solution
• Purple colour change indicates that proteins are present

Question 10

The skin is one of the largest organs in the body. It is
composed of several layers of tissue. The outer layer consists of dead cells packed with keratins. Keratins are a group of proteins that differ from each other in their primary structure. Each keratin molecule consists of several polypeptide chains, each individual chain wound
into a spiral or helix.

Explain how sulphur-containing amino acids help to give keratin molecules their characteristic strength.

Answer 10

• Chemical bonds formed between sulphur-containing groups form stronger disulphide bonds; this binds the protein chains to each other;

Question 11

The skin is one of the largest organs in the body. It is
composed of several layers of tissue. The outer layer consists of dead cells packed with keratins. Keratins are a group of proteins that differ from each other in their primary structure. Each keratin molecule consists of several polypeptide chains, each individual chain wound
into a spiral or helix.

Explain why differences in primary structure
result in keratins with different properties

Answer 11

• Different sequences of amino acids;
• So the tertiary stucture contains bonds in different places which gives different shape

Question 12

In humans, the enzyme maltase breaks down maltose to
glucose. This takes place at normal body temperature.
Explain why maltase:
* only breaks down maltose
* allows this reaction to take place at normal body temperature.

Answer 12

• Tertiary structure of the enzyme maltase means that the active site complementary to maltose
• When the enzyme and substrate bind, stress is being placed on the subsrate’s bonds, which lowers the activation energy, therefore reactions can take place at normal body temperature