# 3.4.3 The Role of Haemoglobin

### The Role of Haemoglobin

#### Transport of oxygen

• The majority of oxygen transported around the body is bound to the protein haemoglobin in red blood cells
• Each molecule of haemoglobin contains four haem groups, each able to bond with one molecule of oxygen
• This means that each molecule of haemoglobin can carry four oxygen molecules (eight oxygen atoms in total)
• When oxygen binds to haemoglobin, oxyhaemoglobin is formed:

4O2 + Hb (Haemoglobin)  → HbO8 (Oxyhaemoglobin)

• Oxygen can also dissolve in the water of blood plasma; at normal body temperatures about 0.025 cm3 of oxygen can dissolve in water
• Cooperative binding takes place – the binding of the first oxygen molecule results in a conformational change in the structure of the haemoglobin molecule, making it easier for each successive oxygen molecule to bind
• The reverse of this process happens when oxygen dissociates in the tissues
• The dissociation of the last oxygen molecule is the hardest

#### Worked Example

There is around 150 g of haemoglobin in 1dm3 of blood.
In a healthy adult at room temperature, 1 g of haemoglobin can combine with 1.4cm3 of oxygen.

Calculate how much oxygen can be carried in 1dm3 of blood.

To answer this question, we must look at the information already given to us in the question. You do not need prior knowledge to gain full marks here.

In 1 dm3 of blood, there is 150 g of haemoglobin.

1 g of haemoglobin can carry 1.4 cm3 of oxygen.

Step One: Find the scale factor between 1g and 150g

150g ÷ 1g = 150

Scale factor = 150

Step Two: Multiply the volume of oxygen carried by the scale factor

1.4 cm3 x 150 = 210 cm3

Therefore 150 g of haemoglobin can carry 210 cm3 of oxygen.

210 cm3 is the final answer.

#### Exam Tip

In mathematical questions, remember that 1000 cm3 equals 1 dm3

### Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.
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