Protein Structure

Question 1

Primary Structure

Answer 1

The primary structure is the sequence in which the amino acids are synthesised into the polypeptide

(The amino-acid sequence determines the protein structure and, hence, the function of the protein)

Question 2

Secondary Structure

Answer 2

Secondary structure is stabilised by hydrogen bonds along the backbone of the polypeptide strand. The hydrogen bonds exist between different peptide bonds in the chain.

3 types of secondary structure -

• alpha helices
• parallel or antiparallel beta-pleated sheets
• turns

Question 3

Tertiary Structure

Answer 3

The polypeptide folds into a tertiary structure.

This conformation is stabilised by interactions
between R groups: 
- hydrophobic interactions
- ionic bonds
- London dispersion forces
- hydrogen bonds
- disulfide bridges 

(Disulfide bridges are covalent bonds between
R groups containing sulfur.)

Question 4

Quaternary Structure

Answer 4

Quaternary structure exists in proteins with two or more connected polypeptide subunits.

Quaternary structure describes the spatial arrangement of the subunits.

Question 5

Prosthetic Groups

Answer 5

A prosthetic group is a non-protein unit tightly bound to a protein and necessary for its function.

(The ability of haemoglobin to bind oxygen is dependent upon the non-protein haem group)

Question 6

Interactions of the R groups can be influenced by temperature and pH

Answer 6

Temperature - Increasing temperature disrupts the interactions that hold the protein in shape; the protein begins to unfold, eventually becoming denatured.

pH - The charges on acidic and basic R groups are affected by pH. As pH increases or decreases from the optimum, the normal ionic interactions between charged groups are lost, which gradually changes the conformation of the protein until it becomes denatured.