Unit 12 -> Haemoglobin

What type of structure does Hb have?

Quaternary - 4 polypeptide chains

What is the role of Hb?

To transport oxygen around the body by loading and unloading it

What shape does a RBC have and why?

• It has a biconcave shape to give it a larger SA:V so that oxygen can diffuse into the cell more rapidly

• No nucleus so more space for Hb so more oxygen can be carried

What is each Hb composed of?

4 sub units each containing a Haem group at its centre

How many oxygen molecules can one haem group bind with?

4 as they have 4 haem groups that can each bond to 1 oxygen molecule

When is oxyhaemoglobin formed?

When Hb associates with oxygen in areas with a high ppO₂

Oxyhaemoglobin disassociates with oxygen in an area with a lower ppO₂

What is partial pressure?

The amount of a particular gas in a mixture of gases or a solution

What shape does an ODC have?

Sigmoid or S shaped

What is loading?

Oxygen is taken up by Hb

What is unloading?

When oxygen is given up by Hb

What is meant by affinity?

attraction

Why is oxygen taken up in the lungs?

• there is a higher ppO₂

• Hb has a high affinity for oxygen

• Oxygen loads more readily so there is a higher % saturation of haemoglobin

Why is oxygen unloaded at respiring tissues?

• low ppO₂

• Hb has a low affinity for oxygen

• Oxygen unloads more readily giving Hb a lower % saturation

Why does CO₂ cause oxygen to unload at respiring cells?

• CO2 dissolves in the blood which lowers the pH

• pH changes away from the optimum for Hb

• causes H/ ionic bonds in the tertiary to break

• alters the shape of the binding sites

• this causes oxygen to unload more readily

What is co operative binding?

The binding of one molecule of oxygen makes it easier for the second one to bind

How does co operative binding occur?

• 1st oxygen binds which causes a change in tertiary structure

• allows more oxygen to bind more easily as it uncovers another active site with the Fe ion

• Hb becomes more saturated

How is co operative binding shown on the ODC?

At low ppO₂ there is little increase in saturation of Hb until the 1st oxygen molecule binds and then there is a rapid rise as it becomes easier for the oxygen to bind

What is the advantage of co-operative binding?

It allows for rapid loading of oxygen in the lungs and rapid unloading at respiring tissues

What is the bohr shift?

The effect of the increase in Co2 concentration of the disassociation of oxyhaemoglobin

What happens when the ODC is shifted to the right?

• there’s a high ppCO₂

• ODC shifts to the RIGHT

• Hb now has a reduced affinity for oxygen

• more oxygen is unloaded

• Higher respiration rates

• examples are animals with high metabolic rate- very active or small and lose heat due to large SA:V

Why do different animals have different types of Hb?

They have an altered primary structure

What happens when the ODC is shifted to the left?

• curve shifts to the left

• Hb has a higher affinity for oxygen

• becomes fully saturated at lower ppO₂

• examples are foetal hb, high altitudes