3B Haemoglobin

Question 1

Where is haemoglobin found and what is its function?

Answer 1

It is found in red blood cells and its role is to carry oxygen around the body.

Question 2

What animals have haemoglobin?

Answer 2

All vertebrates, and also earthworms, starfish, some insects and plants, and some bacteria.

Question 3

Describe the structure of haemoglobin.

Answer 3

Haemoglobin is a large protein with a quaternary structure.

It is made up of four polypeptide chains.

Question 4

Describe the properties of the polypeptide chains in haemoglobin.

Answer 4

Each chain has a haem group which contains an iron ion an gives haemoglobin its red colour.

Question 5

How many molecules of oxygen can a single haemoglobin molecule carry?

Answer 5

Four.

Question 6

What is haemoglobin called when it combines with oxygen?

Where does this occur and what is this process called?

Answer 6

In the lungs.
This is called association or loading.
Oxyhaemoglobin is formed.

Question 7

What molecule is formed when oxygen leaves oxyhaemoglobin?

Where does this occur and what is this process called?

Answer 7

This occurs near body cells in respiring tissue.
The process is called dissociation or unloading.
The oxyhaemoglobin becomes haemoglobin again.

Question 8

What is the equation for the processes of unloading and loading of oxygen on haemoglobin?

Answer 8

Hb + 4O2 HbO8

Question 9

What is affinity for oxygen?

Answer 9

The tendency a molecule has to bind with oxygen.

Question 10

Describe partial pressure of oxygen (pO2)

Answer 10

This is one of the conditions that affects haemoglobin’s affinity for oxygen.
It is a measure of oxygen concentration, ie. the concentration of dissolved oxygen in cells.

Question 11

How does pO2 affect haemoglobin’s affinity for oxygen?

Answer 11

As pO2 increases, haemoglobin’s affinity for oxygen increases.

Question 12

Describe the pO2 when haemoglobin is loading and unloading oxygen.

Answer 12

In the lungs there’s a high pO2 as oxygen enters through the alveoli. Oxygen loads onto haemoglobin to form oxyhaemoglobin.

When cells respire they use up oxygen, so in respiring tissue there’s a lower pO2. Red blood cells deliver oxyhaemoglobin to these tissues where it unloads its oxygen.

Question 13

What does an oxygen dissociation curve show?

Answer 13

How saturated haemoglobin is with oxygen at any given partial pressure.

Question 14

How does affinity for oxygen affect saturation of oxygen?

Answer 14

The higher the affinity for oxygen the more saturated the haemoglobin is with oxygen, and vice versa.

Question 15

How does saturation of oxygen affect affinity of haemoglobin, and how does this change the shape of the dissociation curve?

Answer 15

When haemoglobin first combines with an oxygen molecule its shape changes making it easier for other molecules to join, too. But eventually the haemoglobin becomes so saturated that it gets harder for oxygen molecules to join. As a result the curve is steeper in the middle- S shaped.

Question 16

How is partial pressure measured?

Answer 16

Pa, pascals, or kPa, kilopascals.

Question 17

What is partial pressure of carbon dioxide?

Answer 17

PCo2 is a measure of the concentration of CO2 in a cell.

Question 18

How does pCO2 affect oxygen affinity and why is this useful?

Answer 18

Haemoglobin gives up oxygen more readily at a higher PCO2 and less readily at low PCO2.
When cells respire they release carbon dioxide increasing the pCO2. This increases the rate of oxygen unloading so respiring tissues get as much oxygen as possible.

Question 19

What is the Bohr effect?

Answer 19

Organisms that have a higher pCO2 in their blood will have a lower affinity for oxygen. The saturation of blood with oxygen is lower for a given pO2, so their dissociation curve will shift to the right.
Organisms that have a lower pCO2 in their blood will have a higher affinity for oxygen. So their dissociation curve will shift to the left. The saturation of blood with oxygen is higher for a given pO2, so their dissociation curve will shift to the left.

Question 20

How does a low oxygen concentration environment (ie. burrows, high altitudes) affect the dissociation curve of an organism?

Answer 20

Organisms living in environments with poor oxygen concentrations have haemoglobin with a higher affinity for oxygen than human haemoglobin. So their saturation of blood with oxygen at any given pO2 is higher and their curve shifts to the left of ours.
E.g. Lugworm living in burrows under sand!

Question 21

How does organisms having high activity levels affect the dissociation curve?

Answer 21

Organisms that are very active and have a high oxygen demand have haemoglobin with a lower affinity for oxygen that human haemoglobin. This is so oxygen can be easily unloaded. Their saturation of blood with oxygen at any given pO2 is lower, and so their dissociation curve shifts to the right.
E.g. a Hawk which is very active.

Question 22

How does the size of an organism affect its dissociation curve?

Answer 22

Small mammals have a higher surface area to volume ratio so lose heat more quickly. They have a high metabolic rate to keep them warm meaning a high oxygen demand. So their haemoglobin has a lower affinity for oxygen in order to unload it easily. The saturation of oxygen is lower at any given pO2 so their curve is to the right of the human curve.
E.g. A mouse is much smaller than a human so its curve is shifted to the right.