Haemoglobin

What is haemoglobin?

A water-soluble globular protein consisting of two beta and two alpha polypeptide chains, with a quaternary structure.

How does haemoglobin transport oxygen?

Oxygen enters the lungs from the air and then needs to be transported to body cells via blood

In the capillaries in the lungs, oxygen binds to iron in haem groups forming oxyhaemoglobin

Oxyhaemoglobin can be transported via blood to respiring body tissues

At respiring tissue, oxygen dissociates from haemoglobin

What does haemooglobin contain?

Red blood cells contain haemoglobin, which has 4 haem (Fe2+) groups

Therefore each haemoglobin molecule can carry 4 oxygen molecules,

What is the significance of the iron ion in haemoglobin?

The iron ion gives haemoglobin its red color and is essential for binding oxygen.

What does haemoglobin saturation with oxygen depend on?

Haemoglobin (Hb) saturation with oxygen depends on the the partial pressure of oxygen

How can you show the saturation of haemoglobin with oxygen and partial pressure of oxygen

On a graph called a oxygen dissociation curve with the partial pressure of oxygen on the x-axis and the saturation of haemoglobin with oxygen on the y-axis

what is the units for partial pressure?

kilopascals (kPa)

What happens at a high partial pressure of oxygen and relate it to to graph?

At a high partial pressure (at the lungs) of oxygen haemoglobin has a high affinity for oxygen so more readily loads/associate with oxygen and so there is a higher saturation of haemoglobin with oxygen

What happens at a low partial pressure of oxygen and relate it to the graph?

At a lower partial pressure (at respiring body cells) haemoglobin has a lower affinity for oxygen so haemoglobin more readily unloads/dissociates and so there is a lower saturation of haemoglobin with oxygen

Explain cooperative binding and then also relate this to the graph

When haemoglobin combines with the first oxygen molecule, its tertiary structure alters in a way that makes it easier for oxygen molecules two and three to bind hence the steep increase in the graph

But as haemoglobin starts to become saturated it gets harder for the fourth oxygen molecules to find a binding site. As a result the curve has shallow areas at each end where it's harder to find a binding site

What shape does the oxygen dissociation curve of haemoglobin have?

An S-shaped (sigmoid) curve.

Why does foetal haemoglobin differ from adult haemoglobin?

Foetal haemoglobin differs from adult haemoglobin because:

The foetus needs to obtain oxygen from the mother's blood but the foetus encounters maternal blood with a lower partial pressure of oxygen

This means that foetal haemoglobin has a higher oxygen affinity than the adult haemoglobin found in the mother's blood

This allows the oxygen to dissociate from the mother's haemoglobin, and bind with haemoglobin in the foetal blood.

This ensures that the foetus gets enough oxygen to survive while it develops

How does the graph show that foetal hemoglobin is different to adult haemoglobin?

on the graph the curve is shifted to the left.

Showing that a lower partial pressure (compared to adult haemoglobin) has a higher saturation of haemoglobin with oxygen percentage

What else can also effect the affinity of haemoglobin for oxygen ?

the partial pressure of carbon dioxide

What is the Bohr effect?

Haemoglobin has a lower affinity for oxygen at higher partial pressures of carbon dioxide

When cells respire they produce carbon dioxide which raises the partial pressure of carbon dioxide

This causes the pH of the blood to fall which leads to a change in haemoglobin shape

This results in the haemoglobin affinity for oxygen to fall, causing oxygen to be released more readily.

This is known as the Bohr effect

How does the Bohr effect apply to physical activity?

It means that during physical activity where there is an increase in the partial pressure of carbon dioxide, due to the lower affinity of haemoglobin for oxygen, oxygen can be provided to respiring cells to allow aerobic respiration.

What effect does the Bohr effect have on the curve?

The Bohr effect shifts the oxygen dissociation curve to the right, showing that at a higher partial pressure the saturation of haemoglobin with oxygen is lower when there is high partial pressure of carbon dioxide.

What does an organisms type of haemglobin depend on?

An organism's activity levels, environment and size will affect the type of haemoglobin they have

How does the environment effect the type of haemoglobin in an organism and how does this show on the curve

Animals that live in areas with low partial pressures of oxygen, such as lugworms who burrow in sand and are covered by sea water for much of the time, llamas, who live at high altitudes and foetuses who are receiving their oxygen through a placenta have haemoglobin that is adapted to load oxygen, even at low partial pressures.

They have haemoglobin with a higher affinity for oxygen than human haemoglobin so the dissociation curve is to the left of ours

How does the size effect the type of haemoglobin in an organism and how does this show on the curve

Small animals with a large surface area to volume ratio have a high metabolic rate (a higher rate of heat lost). This means that they have a high rate of respiration and an increased respiration will result in an increased concentration of CO2,

They will have haemoglobin with a lower affinity for oxygen, therefore the oxygen dissociation curve will shift to the right (Bohr Effect)

How does activity level effect the type of haemoglobin in an organism and how does this show on the curve

Organisms that are very active have a haemoglobin with a lower affinity for oxygen than human haemoglobin so the curve shifts to the right (Bohr Effect)

This curve can be shifted even more to the right if the organism is in a place where there is plenty of available oxygen.

What is the relationship between surface area to volume ratio and metabolic rate in small animals?

Small animals with a high surface area to volume ratio have a high metabolic rate and require haemoglobin with a lower affinity for oxygen.

What role does carbon dioxide play in haemoglobin's oxygen affinity?

Higher partial pressures of carbon dioxide decrease haemoglobin's affinity for oxygen, promoting oxygen release.

What does the term 'partial pressure' refer to in the context of gases?

The pressure exerted by a single type of gas in a mixture of gases, measured in kilopascals (kPa).

What is oxyhaemoglobin?

Haemoglobin that has bound to oxygen, allowing for transport to body tissues.

What happens to the oxygen dissociation curve during physical activity?

It shifts to the right due to increased carbon dioxide levels, indicating lower saturation of haemoglobin with oxygen.

What is the significance of the S-shaped curve in haemoglobin saturation?

It indicates that small changes in partial pressure of oxygen can lead to significant changes in haemoglobin saturation.

How does the structure of haemoglobin change upon binding with oxygen?

The tertiary structure alters to facilitate easier binding of additional oxygen molecules.

What is the effect of pH on haemoglobin's affinity for oxygen?

A lower pH (more acidic) decreases haemoglobin's affinity for oxygen, promoting oxygen release.

What is the role of haem groups in haemoglobin?

Haem groups contain iron ions that bind to oxygen, enabling oxygen transport.

What does a rightward shift in the oxygen dissociation curve indicate?

It indicates a lower affinity of haemoglobin for oxygen, often due to increased carbon dioxide levels.

What is the significance of the term 'haem' in haemoglobin?

Haem refers to the iron-containing component of haemoglobin that binds oxygen.

What adaptations do llamas have regarding their haemoglobin?

Llamas have haemoglobin with a higher affinity for oxygen, allowing them to thrive at high altitudes.