Lecture 11: Haemoglobin 1

Question 1

What is the main role of myoglobin?

Answer 1

The primary function of myoglobin is to store oxygen to supply to the muscle.
It alone can only supply the muscle for up to 7 seconds

Question 2

What is the main role of haemoglobin?

Answer 2

To transport oxygen (O2) from the lung to tissues, binding and releasing O2 in a cooperative manner

Question 3

What are the two major components of a myoglobin or haemoglobin
molecule?

Answer 3

Haem group for oxygen to bind to iron and a globin fold that creates a hydrophobic pocket within the molecule
Shift from dull to bright red allows monitoring O2 binding.

Question 4

What is a haem group and what are its properties?

Answer 4

Haem includes four pyrrole rings linked together in a plane. (nitrogen)
Iron (Fe) has six coordinate bonds – four to nitrogen atoms of the haem, one to a nitrogen atom of histidine F8 the globin, one to O2

Question 5

How many subunits make up myoglobin versus haemoglobin?

Answer 5

Myoglobin is a monomer (1)
Haemoglobin is a tetramer (4)

Question 6

Fe2+ has six coordination bond sites, what binds to each of these sites?

Answer 6

4 Nitrogens of the haem
1 Nitrogen of the Histodine F8
1 to an Oxygen

Question 7

What is the role of His E7 in myoglobin?

Answer 7

has been proposed to act as a gate with an open or closed conformation controlling oxygen access to the active site.

Question 8

Select the correct options:
Myoglobin is O2 saturated at low/high pO2, and releases O2 at
very low/high cellular pO2

Answer 8

Low pO2
very Low pO2

Question 9

What is the maximum number of O2 molecules that may be bound to a haemoglobin tetramer?

Answer 9

Four oxygens

Question 10

Describe the changes that occur in myoglobin or haemoglobin upon oxygen binding and release.

Answer 10

1. HisF8 Binds Fe out of plane
2. Oxygen-binding bring Fe in-plane
3. Additional Histidine on opposite side of haem distorts gas binding (Allows dissociation and therefore delivery of O2 to the cell)

Question 11

T-State means high/low O2 affinity?

Answer 11

Tense state = low affinty

Question 12

R-State means high/low O2 affinity?

Answer 12

Relaxed state = high affinity

Question 13

Myoglobin versus haemoglobin:

Answer 13

• Store in tissue versus transport molecule
• Monomer versus tetramer
• Tighter, hyperbolic binding versus weaker sigmoidal binding curve —>Co-operativity of haemoglobin

Question 14

Define Cooperativity:

Answer 14

• Requires multiple interacting subunits - oligomer
• Co-operativity generates a sigmoidal binding curve.
• Shifts binding affinity (and the steep part of the binding curve) to a physiologically relevant concentration (O2 in hemoglobin).

Question 15

Define allostery:

Answer 15

• Can occur in monomeric or multiple subunit proteins/enzymes
• Involves regulators or posttranslational modifications away from the active site
• Can be linked with co-operativity

Question 16

What gives haem its red colour?

Answer 16

The molecular electronic orbitals

Question 17

What makes up the different structures (primary, secondary etc.) of globin proteins?

Answer 17

Primary: ~ 150 amino acids
Secondary: eight α-helices A-H and connecting loops
Tertiary: globin fold with hydrophobic pocket - haem binds in pocket interacting with His F8
Quaternary (not myoglobin): Monomer in a single polypeptide chains