Protein Bonds In Protein Structure

Question 1

Which bonds maintain protein primary structure?

Answer 1

Covalent peptide bonds

Question 2

Which bonds maintain protein secondary structure?

Answer 2

Hydrogen bonds

Question 3

Which bonds maintain protein tertiary and quaternary structure?

Answer 3

1. Covalent disulphide
2. Ionic
3. H bonds
4. Van der Walls
5. Hydrophobic

Question 4

What are disulphide bonds and in which proteins are they commonly found?

Answer 4

• Strongest (214 kJ/mol)
• Formed between Cys residues: lose 2H+ and 2e- (from -SH -SH to -S -S).
• Limits protein folding but helps maintain structure.
• Present mainly in proteins that are secreted or in hostile environment (e.g. Ribonuclease in the gut)

Question 5

What can disulphide bonds be broken by?

Answer 5

Reducing agents, e.g. Beta-mercaptoethanol.

Question 6

What are electrostatic interactions?

Answer 6

• Relatively weak, 10-30 kJ/mol

- Formed between charged groups (salt bridges), e.g. Glu-, Asp- and Arg+, Lys+

Question 7

What are hydrogen bonds?

Answer 7

• Polarised, 10-30 kJ/mol

- Formed between an electronegative atom and a hydrogen bound to another electronegative atom.

Question 8

What is the hydrophobic effect?

Answer 8

• ~10kJ/mol

- Interaction between hydrophobic side chains due to displacement of water.

Question 9

What are van dear Wales forces?

Answer 9

• 4 kJ/mol
• dipole-dipole interactions
• Important when surfaces of 2 large molecules come together.

Question 10

What is protein denaturation?

Answer 10

• Disruption of protein structure due to breaking of forces holding proteins.
• E.g. Heat increases vibrational energy
  pH alters ionisation state of aa and changes ionic/H bonds
  Organic solvents disrupt hydrophobic interactions

Question 11

Describe the process of protein folding.

Answer 11

• Ordered process (or would take too long)
• Each step involves localised folding with stable conformations maintained
• Driven by need to find most stable conformation.

Question 12

Name diseases caused by protein misfolding.

Answer 12

• AMYLOIDOSES involve amyloid fibres
  
  • misfolded, insoluble form of normally soluble protein
  • highly ordered with a high degree of beta-sheet

E.g. Alzheimer’s, T2 diabetes, Parkinson’s, Spongiform encephalopathies