Biology- oxygen transport

Haemoglobins are a group of chemically similar molecules

They are made from 4 polypeptide chains, so have a quaternary structure

Found in red blood cells

Structure of haemoglobin:

Oxygen loads to haemoglobin to form oxyhemoglobin

Co-operative nature of oxygen binding

1. First the oxygen molecule binds

2. This causes a change in shape of the haemoglobin

3. Which makes it easier for other oxygen molecules to bind

Affinity of oxygen

How readily haemoglobin loads with oxygen is called its affinity for oxygen.its affinity for oxygen changes as oxygen concentration varies through the body.

At the gas exchange surface:

• Partial pressure of oxygen is high

• Oxygen diffuses down concentration gradient from alveoli into red blood cells

• Hb has a high affinity for oxygen(due to high partial pressure)

• So loads with oxygen readily

• Co-operative nature occurs ( first oxygen molecule binds to haemoglobin and changes its shape so rest of oxygen binds easier.

• Red blood cells travel in blood to tissues

At the tissues:

• Partial pressure is lower

• Oxygen has a lower affinity

• So oxygen unloads

• Oxygen diffuses down concentration gradient from RBC to the tissues

Region of body= lungs → oxygen partial pressure high → high affinity for oxygen → oxygen loads to hb

Region of body= respiring issues → oxygen partial pressure high → affinity for oxygen is low → oxygen unloads to hb