Haemoglobin and Oxygen Dissociation Curves

Aims To describe the structure and function of Haemoglobin. To be able to sketch, label and analyse an oxygen dissociation curve. To understand the Bohr Effect. Relate the type of Hb an organism has to its environment and way of life.

Can you recall? Which component of the blood transports oxygen? Red blood cells. Which molecule present in red blood cells is particularly responsible for oxygen transport? Haemoglobin. Can you recall the structure of haemoglobin from module 1?

to complete the definitions in your handbook of: Use your glossary at the back of your textbook p238-242 to complete the definitions in your handbook of: The primary structure of a protein The secondary structure of a protein The tertiary structure of a protein Which is held together by 3 types of bonds called: The quaternary structure of a protein

Haemoglobin (Hb) Haemoglobin is a globular protein with 4 polypeptide chains bonded together. It therefore has a quaternary structure. There are 4 Haem groups (each contain iron) Each haem group can transport one oxygen molecule O2 How many oxygen molecules can one molecule of haemoglobin carry? 4 This is the same as transporting 8 oxygen atoms! when the haemoglobin is totally saturated with oxygen.

Haemoglobin is a globular protein with a quaternary structure. Haemoglobin consists of 4 polypeptide chains, each with an iron containing haem group. Each haem group can carry one oxygen molecule O2 So, each haemoglobin molecule can carry a maximum of 4 oxygen molecules (8 atoms of oxygen) when the haemoglobin is totally saturated with oxygen.

Haemoglobin (Hb) has a high affinity (attraction) for oxygen so it bonds with oxygen very easily. When haemoglobin associates with oxygen in the lungs it forms oxyhaemoglobin. We say the Hb loads/associates/combines/bonds with oxygen to transport it. This reaction is reversible at the cells. At the respiring tissues the haemoglobin dissociates from it’s oxygen (oxygen is released/unloaded). Haemoglobin gradually dissociates or unloads its oxygen. Hb + O2 HbO2 HbO2 + O2 HbO4 HbO4 + O2 HbO6 HbO6 + O2 HbO8 Haemoglobin associates (or loads) with oxygen. A molecule of haemoglobin fully saturated with oxygen

250 million 1,000 million IT IS IMPORTANT TO UNDERSTAND THAT: There are (approximately) …………………….. haemoglobin molecules inside each separate red blood cell. This means that inside each SINGLE red blood cell all the haemoglobin molecules together can carry a total of (approx)…………………… oxygen molecules. 250 million 1,000 million

TASKS: Use textbook p150-151 to complete the middle section of page 4 of your handbook.

An oxygen dissociation Curve This is a graph that show the relationship between how much oxygen the Hb is carrying and the partial pressure of oxygen in the surrounding tissues.

An oxygen dissociation Curve Percentage saturation of Hb This gives a ‘measure’ of how much oxygen is typically bonded onto the haemoglobin in the blood. Annotate the graph on your HB p4 using this slide and p161 from the handout sheet/Collins textbook. Then do Q7 from the handout sheet/Collins ppO2 Partial Pressure of Oxygen. This gives a measure of the Oxygen Concentration. (Partial Pressure is really: The pressure that one component of a mixture of gases would exert if it were alone in a container). Partial pressure is measured in kilopascals (kPa)

An oxygen dissociation Curve In the Lungs: Haemoglobin in the lungs becomes fully 100% saturated with oxygen (forming oxyhaemoglobin) In theTissues: Haemoglobin dissociates in the tissues to release oxygen for respiration ppO2

ppO2

REMEMBER THAT: Haemoglobin (Hb) can become fully saturated with oxygen in the lungs, but it readily unloads this oxygen to respiring muscles. This gives a characteristic S shaped or sigmoid shaped oxygen dissociation curve. This is because once the first oxygen molecule loads onto Hb, it is easier for the next oxygen to be loaded on.

TASKS: Complete the table and the graph questions on the top of handbook p5 using textbook p151.