Lecture 4 - Protein stability

Question 1

What stabilizes proteins?

Answer 1

bonds and interactions

Question 2

What bonds and interactions stabilize proteins?

Answer 2

• Electrostatic forces
• Hydrogen bonds
• Hydrophobic interactions
• Disulfide bonds

Question 3

Types of electrostatic forces

Answer 3

• Ionic interaction
• Dipole-dipole interactions (van der Waals)
• Hydrogen bonds

Question 4

Ionic interactions in proteins are strong, but do not

Answer 4

greatly stabilize proteins

Question 5

Ion pair or salt bridge

Answer 5

The association of two ionic protein groups of opposite charge

Question 6

The energy of a typical ion pair is about equal to

Answer 6

two free ions (contribute little stability towards native structure)

Question 7

Permanent dipole interactions are generally weaker than

Answer 7

ion pair interactions

Question 8

Permanent dipole moments can be found

Answer 8

between carbonyl and amide groups of the peptide backbone

Question 9

Energy of dipole interactions and London forces

Answer 9

-0.3 kJ/mol

Question 10

Hydrogen bonds occur between

Answer 10

a weakly acidic donor group and an acceptor that bears a lone pair

Question 11

Where are hydrogen bonds located in proteins?

Answer 11

Between N-H and C=O

Question 12

Energy of hydrogen bonds

Answer 12

12-30 kJ/mol

Question 13

Hydrogen bonds only weakly stabilize proteins because

Answer 13

unfolded proteins form hydrogen bonds with water, so hydrogen bonds within proteins are only slightly more stable

Question 14

The strength of hydrogen bonds depends on

Answer 14

the donor-acceptor pair and on their distance

Question 15

Hydrogen bonds are stronger when

Answer 15

the hydrogen bonds lies in the same direction as the N-H covalent bond

Question 16

Gibbs free energy changes for the transfer of a hydrocarbon from an aqueous solution to a nonpolar solvent is

Answer 16

negative

Question 17

Which part of the Gibbs energy equation makes hydrophobic forces so stabilizing?

Answer 17

the entropy component

Question 18

The hydrophobic effect contribution to protein stability resulting from the burial of nonpolar side chains is approximately

Answer 18

5.6 kJ/mol (per residues, so a 100 residue protein will be 560 kJ/mol)

Question 19

A hydropathic index of a protein indicates

Answer 19

which residues are in the protein interior and which are in contact with water

Question 20

Disulfide bonds function to

Answer 20

stabilize the 3D structure of a protein

Question 21

Disulfide bonds form as

Answer 21

proteins fold to their native conformation

Question 22

The primary effect of disulfide bonds on protein denaturation is to

Answer 22

decrease the entropy of the unfolded state