Lecture 4

Question 1

How many polypeptide chains is haemoglobin constructed from? What name describes this number?

Answer 1

4. Tetramer.

Question 2

What is the Mr of haemoglobin?

Answer 2

64,400.

Question 3

What group of note do all 4 subunits of haemoglobin contain?

Answer 3

Haem.

Question 4

What ion of note does the haem group contain?

Answer 4

Fe(II).

Question 5

Is the binding of 4 O2 molecules to tetrameric Hb a reversible process?

Answer 5

Yes.

Question 6

What are the 2 types of polypeptide chains in haemoglobin, and how many of each feature?

Answer 6

α - 2.

β - 2.

Question 7

What shape describes the array of haemoglobin?

Answer 7

Tetrahedral.

Question 8

How do the subunits of haemoglobin differ from myoglobin with regard to polarity? What benefit does this confer to Haemoglobin?

Answer 8

The hydrophobic parts of myoglobin are typically charged in haemoglobin. This enables the haemoglobin subunits to bind together.

Question 9

How many amino acids comprise both α and β chains?

Answer 9

α - 141.

β - 146.

Question 10

What happens to haemoglobin in urea?

Answer 10

It dissolves into 2 αβ dimers.

Question 11

Is there any contact between both α-chains?

Answer 11

A little.

Question 12

Is there any contact between both β-chains?

Answer 12

None.

Question 13

Is there any contact between an α1β1 and α2β2 dimer?

Answer 13

Yes, strong/lots.

Question 14

What 2 reasons ensure that tetrameric Hb is more complicated than monomeric Mb?

Answer 14

Hb transports other molecules as well as O2.

Hb-O2 binding is regulated by 3 molecules.

Question 15

What molecules does Hb transport?

Answer 15

O2, CO2 and H+.

Question 16

What 3 molecules regulate Hb-O2 binding?

Answer 16

H+, CO2, 2,3-Bisphosphoglycerate (2,3-BPG).

Question 17

Are the regulatory molecules bound close to the haem group?

Answer 17

No. Distant.

Question 18

What are allosteric interactions?

Answer 18

When one molecule binds to another molecule causing a conformational change, affecting its operation/activity.

Question 19

What word describes the shape of the Mb saturation curve?

Answer 19

Hyperbolic.

Question 20

What word describes the shape of the Hb saturation curve?

Therefore, what type of binding is Hb-O2?

Answer 20

Sigmoidal.

Positive Co-operative.

Question 21

What does co-operative binding mean in the context of Hb-O2 (i.e. how does one oxygen affect successive oxygens binding?)

Answer 21

Binding of O2 at one haem enhances binding of O2 to the other haems.

Question 22

What is the benefit of co-operative binding for Hb?

Answer 22

Makes Hb a more efficient transporter. Can deliver twice as much O2 as it would if sites were independent.

Question 23

Definition of p50 w.r.t. Hb?

Answer 23

The partial pressure at which sites are half filled.

Question 24

What is the p50 of O2 in RBCs?

Answer 24

26.6mmHg.

Question 25

What binds O2 more tightly, Hb or Mb?

Answer 25

Mb by order of magnitude (p50 = 2.75mmHg).

Question 26

What is the problem with pure Hb without regulators?

Answer 26

Binds oxygen too tightly for physiological needs.

Question 27

What is the p50 of pure Hb?

Answer 27

2-5mmHg.

Question 28

What do the regulators do? What benefit do they confer to Hb?

Answer 28

Each weakens oxygen affinity. Enables Hb to offload O2 better.

Question 29

What is the byproduct formed via anaerobic exercise, which in turn produces H+?

Answer 29

Lactic acid.

Question 30

How can CO2 make blood more acidic?

Answer 30

When it dissolves and ionises in the blood, H+ can be produced.

Question 31

What is the Bohr effect?

Answer 31

A lowered blood pH causes the oxygen dissociation curve to shift to the right, releasing more O2.

Question 32

What does the Bohr effect enable w.r.t the delivery of oxygen during exercise?

Answer 32

Enables more to be delivered, without oxygen tension falling.

Question 33

Which two equations can explain the acidification of the blood when CO2 dissolves?

Answer 33

CO2 + H2O HCO3- + H+. | CO2 + R.NH2 R.NH.COO + H+.

Question 34

What molecule acts as an allosteric regulator?

Answer 34

CO2.

Question 35

When CO2 reacts with N-terminal α-amino groups, what is formed?

Answer 35

Carbamates.

Question 36

What reaction is 2,3-BPG produced from, and where?

Answer 36

Glycolysis, RBCs.

Question 37

What concentration is 2,3-BPG produced at. Also, what is it the same concentration as?

Answer 37

4-5mM. | Same as haemoglobin.

Question 38

Specifically, what type of Hb does 2,3-BPG bind to, and whereabouts?

Answer 38

Deoxyhaemoglobin. | One molecule binds between two β-subunits of Hb.

Question 39

What effect does 2,3-BPG have on the oxygen dissociation curve for Hb?

Answer 39

Displaces to the right, weakening oxygen affinity.

Question 40

Why is BPG physiologically important?

Answer 40

Hb would otherwise unload little oxygen in passing through tissue capillaries, as pO2 there is ~26mmHg.

Question 41

What effect does an increase in temperature have on Hb-O2 dissociation curve? An example of when this could be beneficial?

Answer 41

Displaces to the right, weakening oxygen affinity and releasing more O2. Active muscle.