Blood / haemoglobin

Structure of haemoglobin

• Globular

• water soluble

• Consisted of four polypeptide chains Each carrying a haem group - (quaternary structure)

• Each haem group contains and iron ion giving blood the red colour

Role of haemoglobin

Present in red blood cells - oxygen molecules bind to the haem group and are carried around the body to where they are needed in respiring tissues

Haemoglobin has a high affinity for oxygen

Takes up oxygen more easily and releases it less easily

How does partial pressure of oxygen affect the binding of oxygen to haemoglobin

As pO2 increases haemoglobin affinity for oxygen increases so oxygen binds tightly to haemoglobin. When pO2 is low oxygen is released from haemoglobin

Bohr effect

When the partial pressure of carbon dioxide (pCO2) increases the conditions become more acidic causing haemoglobin to change shape, the affinity of haemoglobin for oxygen then decreases and oxygen is released.

How does the saturation of haemoglobin with oxygen affect the oxygen haemoglobin binding

1. Hard for the first molecule to bind

2. Haemoglobin changes shape too make it easier for the other molecules to bind

3. Becomes slightly harder for the fourth oxygen molecule to as there is a lower chance of finding the binding site

Explain why oxygen binds to haemoglobin in the lungs

pO2 is high

Low concentration of co2 in lungs so affinity is high

Positive cooperativity

What does a oxyhaemoglobin dissociation curve show

• saturation of haemoglobin with oxygen plotted against the partial pressure of oxygen

• Curves further to the left show that haemoglobin has a higher affinity for oxygen

How does carbon dioxide affect them position of an oxyhaemoglobin dissociation curve

Shifts to the right because haemoglobin’s affinity for oxygen has decreased