Q/A Session 2 Flashcards
How many subunits does haemoglobin have?
- 4
- 2x alpha and 2x beta subunits
What does each unit consist of?
- A globin (protein part)
- A heam (non-protein part)
A large portion of the haem group is
non-polar
Haem Fe can bind how many ligands?
6 ligands
How many of those 6 ligands are occupied by N atoms?
4/6
What state must Fe be in for O2 to bind?
Fe2+
What Histidine side chain is the N atom of?
HisF8
-Alpha helix F, 6=6aa of the helix
HisF8 is also referred to as the
Proximal histidine
What is the role of HisF7?
- Prevents oxidation of haem Fe2+ when O2 binds (through a non-linear bond forming which sterically pushes 02 when it binds)
- Ensures weak binding of O2 to ensure binding is reversible
HisF7 is also referred to as the
Distal histidine
T state means what and explain in reference to O2 affinity
T state= tense
Low O2 affinity
R state means what and explain in reference to O2 affinity
R state= relaxed
High 02 affinity
What state would you want to be in when exercising?
T state where there is low affinity to O2 so it will be released into surrounding tissues
When is BPG produced?
When we ‘do work’ and break down carbohydrates
When does BPG bind?
In the T state. It stabilises it keeping in the T state
BPG is known as what kind of regulator?
An allosteric regulator
How many negative charges does BPG carry?
5 negative charges
What state does fetal heamoglobin spend most time?
- R state. Binds O2 better and doesn’t release it.
- The pocket is more negative due to change in aa therefore BPG won’t bind as effectively
The Sequential Model shows
Different subunits can be in different configurations
Concerted model shows
ALL subunits are ALWAYS in the same configuration
What gives the sigmoidal curve?
Cooperativity
What curve shape does haemoglobin show?
Sigmoidal
What curve shape does myoglobin show?
Hyperbolic
What model does Hb follow?
Concerted but has features of the sequential model
What is an allosteric site?
Site on protein that’s not the active site, a regulatory molecule can bind here.
What is an allosteric regulator?
Regulatory molecule that binds to allosteric site
What is allosteric regulation?
Regulation of a molecule by binding an allosteric regulator to an allosteric site
What is the Bohr effect?
Hemoglobin’s oxygen binding affinity is inversely related both to acidity and to the concentration of carbon dioxide
What are three examples of allosteric regulators?
BPG, CO2, H+
What state do they favour?
T state
What is the effect of increased CO2?
- Decrease in pH
2. Lowers affinity for O2
Effect on O2 binding, BPG, CO2, pH, and H+ in R state
- O2 binding favoured
- Decrease in BPG
- Decrease in CO2
- Increase in pH
- Decrease in H+
Effect on O2 binding, BPG, CO2, pH, and H+ in T state
- O2 release favoured
- Increase in BPG
- Increase in CO2
- Decrease in pH
- Increase in H+
What happens in the MetHb condition?
The haem iron has been oxidised
