Module 3: V3 - V4

Question 1

Could myoglobin be used to transport O2?

Answer 1

no, because myoglobin binds very tightly to oxygen in the lungs, however it will not be released in the tissues as the partial pressure will not be low enough (4 kPa&raquo_space; 0.3 kPa)

Question 2

What is the P50 of oxygen (the partial pressure at which it is half saturated)?

Answer 2

0.3 kPa which is really low

Question 3

What is pO2 in the lungs and in tissues?

Answer 3

13 kPa in the lungs and 4 kPa in the tissues

Question 4

Would lowering the affinity (P50) of myoglobin to oxygen help?

Answer 4

no, because this means myoglobin would not bind to oxygen as well which would reduce the overall efficiency of transport

Question 5

What does hemoglobin respond to?

Answer 5

O2 concentration, blood pH, presence regulators and can take CO2

Question 6

Why is hemoglobin useful for oxygen transport?

Answer 6

because it binds very tightly to oxygen in the lungs (almost 100% saturation) and readily releases oxygen in the tissues (60% saturation or even lower during exercise)

Question 7

What are the two conformational states of hemoglobin?

Answer 7

high affinity binding and low affinity binding

Question 8

What is the factor that causes hemoglobin to switch between conformational states? Which conformational state will hemoglobin be in under low concentrations and high concentrations of oxygen?

Answer 8

oxygen concentration
low affinity binding state at a low concentration of oxygen and high affinity binding state at a high concentration of oxygen

Question 9

What is the low affinity state of hemoglobin called and what are its characteristics?

Answer 9

the t (tense) state
more interactions, more stable and lower affinity for O2

Question 10

What is the high affinity state of hemoglobin called and what are its characteristics?

Answer 10

the r (relaxed) state
fewer interactions, more flexible and higher affinity for O2

Question 11

What does O2 binding trigger in hemoglobin?

Answer 11

O2 binding triggers a conformational change from the T state to the R state

Question 12

What does the conformational change in hemoglobin involve?

Answer 12

involves breaking salt bridges between the residues at the α1-β2 interface

Question 13

What is the T state of hemoglobin stabilised by and what causes the conformational change to the R state?

Answer 13

stabilised by a variety of salt bridge interactions

oxygen binding destabilises these interactions and allows transition to the R state

Question 14

What are the most important interactions that stabilize T state hemoglobin?

Answer 14

the salt bridge between His HC3 and Asp FG1 + the salt bridge between His HC3 and Lys C5
(these contacts are destabilised by oxygen binding to nearby heme rings)

Question 15

Where is His HC3 found when oxygen is bound to hemoglobin?

Answer 15

found in the middle of the protein

Question 16

Why do we use hemoglobin and not myoglobin to transport oxygen around the body?
What has the quaternary structure of hemoglobin got to do with it?

Answer 16

myoglobin binds strongly to oxygen in the lungs like hemoglobin, however it does not release oxygen in the tissues as readily as hemoglobin does
the quaternary structure of hemoglobin allows it switch between conformational states

Question 17

How would you describe a ‘sigmoidal’ curve? How would you describe a hyperbolic curve?

Answer 17

a sigmoidal curve is a curve that takes the shape of an “S”, while a hyperbolic curve is a curve that increases exponentially before reaching an asymptote where it plateaus

Question 18

Is the binding curve for the T state of hemoglobin sigmoidal or hyperbolic? What about the binding curve for the R state?

Answer 18

The binding curve for the T state of hemoglobin is sigmoidal and the binding curve for the R state is hyperbolic