3.6 Structure of proteins

Question 1

What is a peptide? (1 mark)

Answer 1

A polymer made up of amino acid molecules.

Question 2

What does a protein consist of? (1 mark)

Answer 2

One or more polypeptides arranged as complex macromolecules.

Question 3

How many amino acid are commonly found in cells? (1 mark)

Answer 3

20

Question 4

Describe the structure of an amino acid. (4 marks)

Answer 4

A central Carbon with the following attached to it:
An amine group (NH2)
A carboxyl group (COOH)
An R-group (a range of chemical groups different to each amino acid- R)
A hydrogen (H)

Question 5

How do amino acids join? (3 marks)

Answer 5

When the amine and carboxyl groups interact with each other, forming a peptide bond (a type of condensation reaction).

Question 6

What is the bond between two amino acids called? (1 mark)

Answer 6

A peptide bond

Question 7

What are two amino acids bonded together called? (1 mark)

Answer 7

A dipeptide

Question 8

What is formed when many amino acids are joined together by peptide bonds? (1 mark)

Answer 8

A polypeptide

Question 9

What is the condensation reaction between two amino acids catalysed by? (1 mark)

Answer 9

Peptidyl transferase (present in ribosomes)

Question 10

What technique is used to separate amino acids? (1 mark)

Answer 10

Thin Layer Chromatography (TLC)

Question 11

How are amino acids separated using TLC? (5 marks)

Answer 11

1. A thin layer of silica gel is applied to a chromatography plate
2. The amino acids are then added to one end
3. That end is then submerged in the solvent
4. The organic solvent moves through the silica gel
5. The amino acids move at different rates, depending on how much their R-groups interact with the silica gel

Question 12

What is the primary structure of a protein? (1 mark)

Answer 12

The sequence of amino acids.

Question 13

What is the secondary structure of a protein? (3 marks)

Answer 13

Hydrogen bonds can form:
1. within amino acid chain forming an alpha helix shape
2. between polypeptide chains forming a beta pleated sheet

Question 14

What is the tertiary structure of a protein? (1 mark)

Answer 14

The folding of the protein into its final shape.

Question 15

Name the interactions that (may) occur between R-groups in the tertiary structure of proteins. (4 marks)

Answer 15

1. Hydrophobic and hydrophilic interactions
2. Hydrogen bonds
3. Ionic bonds
4. Disulfide bridges

Question 16

What are disulfide bridges and when do they occur between amino acids? (2 mark)

Answer 16

Covalent bonds
Only form between R-groups that contain sulfur.

Question 17

What is the quaternary structure of proteins? (1 mark)

Answer 17

The association of two or more proteins (called subunits).

Question 18

Name the interactions that (may) occur between R-groups in the quaternary structure of proteins. (4 marks)

Answer 18

1. Hydrophobic and hydrophilic interactions
2. Hydrogen bonds
3. Ionic bonds
4. Disulfide bridges

Question 19

Describe the quaternary structure of haemoglobin. (3 marks)

Answer 19

Two alpha protein subunits
Two beta protein subunits
Four haem groups (containing iron)

Question 20

How do you test for proteins, and describe what a positive result looks like?

Answer 20

Add a few drops of Biuret’s reagent to the solution, mix.
Positive result: Violet/purple colour