chapter 6 section 5

Question 1

What does quaternary structure describe?

Answer 1

The arrangement and interaction of multiple protein subunits.

Question 2

Is entropy loss during subunit association favorable or unfavorable?

Answer 2

Unfavorable.

Question 3

What provides a favorable entropy gain in subunit association?

Answer 3

Burying hydrophobic groups.

Question 4

Which types of proteins commonly have quaternary structures?

Answer 4

Proteins with two or four subunits.

Question 5

Can proteins have more than four subunits?

Answer 5

Yes, some proteins have higher numbers of subunits.

Question 6

How are multimeric proteins usually arranged?

Answer 6

As symmetric arrangements of asymmetric subunits.

Question 7

What is an example of a multimeric protein with quaternary structure?

Answer 7

Liver alcohol dehydrogenase.

Question 8

What stabilizes immunoglobulin quaternary structure?

Answer 8

Intermolecular and intramolecular disulfide bonds.

Question 9

What drives subunit association at the quaternary level?

Answer 9

Noncovalent interactions and hydrophobic effects.

Question 10

What does burying hydrophobic surfaces achieve?

Answer 10

It increases system entropy by releasing ordered water molecules.

Question 11

Why is entropy loss unfavorable in subunit binding?

Answer 11

Because the subunits lose freedom of motion when locked together.

Question 12

Which types of forces stabilize quaternary structure besides hydrophobic effects?

Answer 12

Hydrogen bonds, ionic interactions, and van der Waals forces.

Question 13

What is the quaternary structure of hemoglobin?

Answer 13

A tetramer with two α and two β subunits.

Question 14

Why is symmetry common in multimeric proteins?

Answer 14

It allows efficient and stable packing of subunits.

Question 15

What advantage does quaternary structure give enzymes?

Answer 15

Cooperative binding and regulation of activity.

Question 16

How can quaternary structure improve protein stability?

Answer 16

By protecting subunits from denaturation or degradation.

Question 17

What does “multimeric protein” mean?

Answer 17

A protein composed of more than one polypeptide chain.

Question 18

How do disulfide bonds affect quaternary structure?

Answer 18

They covalently link subunits, adding extra stability.

Question 19

What is a common feature of dimeric proteins?

Answer 19

Two identical or similar subunits associating together.

Question 20

What is a heteromultimer?

Answer 20

A protein complex with different types of subunits.

Question 21

What is a homomultimer?

Answer 21

A protein complex with identical subunits.

Question 22

Why are Kd values so small for quaternary interactions?

Answer 22

Because subunit binding is extremely tight and specific.

Question 23

What property of immunoglobulins reflects quaternary structure?

Answer 23

heir Y-shaped arrangement of multiple chains held by disulfide bonds.