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Red blood cells contain haemoglobin.

The structure of a haemoglobin molecule is made up as follows:

Primary structure Consists of four polypeptide chains

Secondary structure Each of the polypeptides chains is coiled into
a helix

Tertiary structure Each polypeptide chain is folded into a
precise shape

Quaternary structure All…

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The Role of Haemoglobin

The role of haemoglobin is to transport oxygen.

To be efficient at transporting oxygen, haemoglobin must:

Readily associate with oxygen at the surface where gas exchange takes place
Readily dissociate with oxygen at those tissues requiring it

Haemoglobin changes its affinity for oxygen under different conditions.…

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In the presence of carbon dioxide, the new shape of the haemoglobin molecule binds more
loosely to oxygen.

As a result haemoglobin releases its oxygen.

Affinity ­ how well it is attracted to oxygen

Affinity of haemoglobin for oxygen under different conditions

Region of body Oxygen Carbon dioxide Affinity of…

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An organism living in an environment with little oxygen requires a haemoglobin
that readily combines with oxygen if it is to absorb enough of it.
Provided that the organisms metabolic rate is not very high, the fact that this form
of haemoglobin does not release its oxygen as readily into…

Page 5

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The higher pH changes the shape of the haemoglobin into one that enables it to load
oxygen readily

The shape also increases the affinity of haemoglobin for oxygen, so it is not released
while being transported in the blood to the tissues

In the tissues, carbon dioxide is produced by…

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The graph of this relationship is known as the oxygen dissociation curve.

Where pO2 is high, haemoglobin
has a high affinity for oxygen so it has a high saturati has a high affinity for oxygen,
it has a high saturation of

Where pO2 is low, haemoglobin
has a…

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There are a number of different types of haemoglobin molecules, each with a different shape
and hence a different affinity for oxygen.

In addition, the shape of any one type of haemoglobin molecule can change under different

These facts both mean that there are a large number of different…

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expelled from the concentration of
organism. oxygen in the
lungs, means
that oxygen is
readily loaded by

Rapidly Muscles Level of carbon Affinity of Oxygen
respiring dioxide is high. haemoglobin for dissociation
tissues oxygen is curve is
reduced, which, shifted to
coupled with the the right.

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A human foetus makes a different kind of
haemoglobin from an adult. Foetal haemoglobin
has a higher affinity for oxygen at low partial
pressures, so its oxygen dissociation curve is
shifted up. A developing foetus obtains its oxygen,
not through its lungs, but from its mother's blood
in the placenta.…

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Mice lose heat very quickly due to their large surface
area: volume ratio, so they have a high metabolic rate to generate more heat. Their tissues
therefore have a constant demand for oxygen for respiration. The oxygen dissociation curve
for mouse haemoglobin is shifted down compared to humans, so plenty…


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