HL Bio - Unit #3.3: Haemoglobin

Haemoglobin

The oxygen transport protein that is carried by red blood cells

• Oxygen reversibly binds to the protein

Heamoglobin composition

Haemoglobin is composed of four subunits which contains a haem group that acts as a binding site for oxygen gas

Max number of oxygen molecules that can be transported by a haemoglobin

4

R-State

A fully saturated state with four oxygen molecules

T-State

Fully unsaturated with no bonded oxygens

Cooperative Binding

Conformational changes occur to surrounding haemoglobin subunits when oxygen binds to one of the subunits

• Essentially when oxygen binds to one subunit, it’s oxygen affinity increases, which in turn causes surrounding haemoglobin subunits oxygen affinity to increase (they then gain oxygens as well) 

  • and the opposite

Oxygen Concentrations (kPA)

Has a positive correlation with oxygen saturation levels

Partial pressure of oxygens rises until

until the percentage saturation reaches 10kPA

Why does the pressure of oxygen rise?

This rise happens when blood flows through the capillaries in alveoli which have a oxygen concentration of 10-13kPa (healthy) → follows a gradient and oxygen than diffuses into the blood

• Now blood is distributed throughout the body which has a kPa of less than 10 (allows for oxygen to diffuse out)

Why the sudden spike in oxygen saturation

Due to cooperative binding, oxygen saturation levels don’t increase in a linear form, but rather in the shape of the sigmoid curve

• Because of this quick affinity change haemoglobin saturation levels go from saturated to unsaturated or vice-versa in a relatively small/narrow range of oxygen concentration (hence the spike)

Foetal Haemoglobin

Blood cells that humans have as foetuse’ in the womb

• These blood cells have much higher oxygen affinities → Causes them to be more saturated with oxygen at all partial pressures of oxygens

• Oxygen from the mothers placenta dissociate and then bind to the haemoglobin in foetal blood 

  • This can only occur with foetal blood, however, because of its high oxygen affinity levels

Adult Haemoglobin

Blood cells that humans have after ~3 months

• These blood cells have lower oxygen affinity levels

• After a baby is born they slowly replace their foetal blood with adult blood in approx 3 months since the oxygen affinity in foetal blood is too high for oxygen processing directly from the lungs rather than the placenta

Bohr shift/effect

which occurs to ensure that respiring tissues have enough oxygen when they require a lot of it

Bhor Shift Process

• Increased aerobic respiration in active tissues results in higher concentrations of CO2 in the lungs, and therefore more CO2 is released into the blood

• Increase in CO2→ easier dissociation of oxygen molecules in haemoglobin

• High CO2 concentrations ( in actively respiring tissues) converts haemoglobin to carbaminohemoglobin, which promotes the dissociation of oxygen

• Low CO2 concentrations (in the lungs) converts carbaminohemoglobin back to haemoglobin, which promotes the affinity of oxygen

Oxygen Dissociation Curves

Represents the percentage that the oxygen fully saturates in haemoglobin at different oxygen concentrations

Partial pressure of oxygen in the atmosphere is

21.2kPa

DIfferent oxygen dissociation curve within fetal and adult hemoglobin

• foetal haemoglobin has a significantly higher oxygen affinity 

  • So even at lower levels of partial pressure of oxygen foetal blood’s high affinity allows for a quicker saturation process 

  • Therefore, Foetal haemoglobin saturated with oxygen at lower partial pressures of oxygen causing it’s spike to be earlier (more to the left)

• While Adult blood needs a higher partial pressure of oxygen in order to saturate with oxygen since it’s oxygen affinity is significantly lower