Module 2 Exchange and transport 1.2.11 Carriage of oxygen

Concept question: How does haemoglobin know where to deliver its oxygen?

Learning Objectives Success Criteria To understand the role of haemoglobin in carrying oxygen To be able to compare fetal and adult haemoglobin curves Explain the meaning of the term affinity (Grade E - D) Describe the role of haemoglobin in carrying oxygen (Grade C –B) Explain the significance of the different affinities for oxygen of foetal haemoglobin & adult haemoglobin (Grade B – A)

Haemoglobin Haemoglobin has a quaternary structure, made up of 4 polypeptide chains. Each polypeptide chain has a haem group A haem group has an iron ion (Fe2+) Each Fe2+ can join to an Oxygen molecule (O2) Total = 4 O2 molecules can be carried by 1 haemoglobin molecule in humans Hb + 4O2 Hb08 Haemoglobin + oxygen Oxyhaemoglobin Students to make sure it can demonstrate loading and unloading loading unloading

The Role of Haemoglobin Main role: to transport oxygen It must: Readily associate (loads) with oxygen at the gas exchange surface eg. lungs Readily dissociate (unloading) from oxygen at the tissues that require it How does it manage this? The shape of haemoglobin changes under different conditions e.g. when CO2 is present: haemoglobin’s shape makes it bind more loosely to O2, so it loses the oxygen It binds more readily at high partial pressures of oxygen

Affinity of haemoglobin for O2 Explain the meaning of the term affinity (Grade E - D) Affinity of haemoglobin for O2 Copy and complete the table Region of body Oxygen Concentration CO2 concentration Affinity of haemoglobin for O2 Result – what happens to oxygen? Gas exchange surface High Low Oxygen is attached Respiring Tissues Oxygen is released Words to use: High, Low, Oxygen is attached, Oxygen is released

The oxygen dissociation curve Shows how much oxygen is combined with haemoglobin at different oxygen concentrations 100 % - every haemoglobin molecule is carrying the max of 4 molecules of oxygen Partial pressure – measure of oxygen concentration in a mixture of gases (greater the concentration of dissolved oxygen in cells the higher the partial pressure) Atmospheric pressure at sea level is 100KPa, so at sea level what is the partial pressure of oxygen? 0 % saturation = none of the haemoglobin molecules are carrying any oxygen

Oxygen Dissociation Curves Why are oxygen dissociation curves S shape. At low oxygen tension: the 4 chains in the haemoglobin are very closely united, making it difficult to load the first oxygen molecule When the oxygen tension rises, the diffusion gradient into the haemoglobin molecule steeply rises. Once loaded, the oxygen causes the shape to alter known as a conformational change so the chains can load the other oxygen molecules easier However as Hb becomes saturated it gets harder for more oxygen to join. It is difficult to reach 100% even at high oxygen pressure, so the curve levels off again. The steep part of the curve are where its easy for oxygen to join and the shallow bits at the end show where it gets harder. The graph of this is called the oxygen dissociation curve

Oxygen Dissociation Curves Other 3 oxygen molecules bind easily Small decrease in partial pressure of O2 leads to a lot of dissociation First oxygen molecule is difficult to bind

Oxygen Dissociation Curves Describe the role of haemoglobin in carrying oxygen (Grade C –B) Oxygen Dissociation Curves May be different for different haemoglobins (in different organisms), but will have a similar shape Will be in a different place on the graph: Further to the left: Greater affinity for O2 Further to the right: Lower affinity for O2 Adult and fetal haemoglobin have different affinities for oxygen. Fetal haemoglobin has a higher affinity for oxygen in lower partial pressures of oxygen (better at absorbing oxygen than it’s mothers blood), this is important as the fetus gets oxygen from its mother’s blood across the placenta. Task – Complete worksheet – page 64 help

Plenary Role play the action of haemoglobin and foetal haemoglobin Fetal haemoglobin curve is shifted to the left Explain the significance of the different affinities for oxygen of foetal haemoglobin & adult haemoglobin (Grade B – A)