3.2.7 - 3.2.8 (transport of oxygen and carbon dioxide)

What is meant by the term affinity?

• A strong attraction

What is meant by the terms association and dissociation?

• Association is when oxygen binds to haemoglobin

• Dissociation is when oxygen is released from haemoglobin

What is the structure of haemoglobin?

• It is a quaternary protein made of 4 polypeptide chains, each one having a haem group.

  • In each haem group there is an iron ion(Fe2+)present

What does the iron in the haemoglobin do?

• It attracts and can hold up to 1 oxygen molecule

Does the haem group have a high or low affinity to oxygen?

• The haem group has a high affinity to oxygen meaning it attracts oxygen easily

How many oxygen molecules can 1 haemoglobin hold?

• It can hold up to 4 oxygen molecules

What is it called when a haemoglobin has all haem groups filled with an oxygen molecule?

• It is a fully loaded haemoglobin

What is meant by the term affinity?

• A strong attraction

What is the haemoglobin become when oxygen binds to it?

• oxyhaemoglobin

Describe how the affinity of haemoglobin to oxygen changes at the lungs and at respiring tissue and why?

• The affinity of haemoglobin to oxygen at the lungs is high as it needs to readily associate with it so it can carry it back to the lungs and then be pumped around the body as oxyhaemoglobin

• The affinity of haemoglobin to oxygen at respiring tissue is low as it needs to dissociate from oxygen at those tissues as they require oxygen for respiration

What does the ability of haemoglobin to associate and dissociate from oxygen depend on?

• It depends on the concentration of oxygen in the surrounding tissue

what is meant by the term partial pressure /oxygen tension?

• Partial pressure is the pressure is created by a gas in a mixture of gases

What is the shape of a haemoglobin dissociation curve in adults?

• It is an S-shaped curve

Why does the haemoglobin dissociation curve in adults form an s-shape curve?

• This is because at low oxygen partial pressure, the haemoglobin doesn’t readily associate with oxygen molecules as the haem group is in the centre of the haemoglobin molecule and so is hard to be reached by the first oxygen molecule leading to a low saturation of oxygen at low partial pressure

• As the oxygen partial pressure increases, and the first oxygen is associated with a haem group, the haemoglobin becomes less tightly bound which called a conformational change in shape. This allows for oxygen molecules to more easily associate with the other haem groups

• The last oxygen molecule is hard to become associated to as the space occupied by the 3 other oxygen molecules , this causes the curve to start to level off.

• When the haemoglobin becomes fully loaded, the saturation of the O2 in haemoglobin reaches near 100%

How is the partial pressure adapted to cause oxygen to associate and dissociate at different parts of the body?

• The partial pressure in the mammalian lungs is sufficient to produce oxygen association close to 100% saturation to be able to transport as much oxygen to respiring tissue as possible

• The partial pressure in respiring mammalian body tissue is sufficiently low enough to cause oxygen dissociation from haemoglobin so it can diffuse into the tissue and be used for respiration

Is the affinity of foetal haemoglobin higher or lower than adult haemoglobin and why?

• It has a higher affinity for oxygen than adult haemoglobin

• This is because it must be able to associate with oxygen from surrounding placenta tissue where partial pressure is already low so that haemoglobin dissociates oxygen so that they can use it for respiration and growth

How does the affinity of foetal haemoglobin being higher than adult mean that there is always oxygen in the placenta?

• Due a higher affinity, oxygen dissociates from maternal haemoglobin in the placenta more easily into the foetal haemoglobin.

• This causes a decrease in partial pressure in the placenta tissue therefore causing oxygen to dissociate from the surrounding blood into the placenta which then repeats the process

What does the graph of a feotal haemoglobin dissociation curve differ to an adult one?

• The graph is shifted to the left

What 3 ways is carbon dioxide transported around the body?

• About 5% is dissolved directly into the plasma

• About 10% is combined directly with haemoglobin to form a compound called carbaminohaemoglobin

• About 85% is in the blood plasma as hydrogen carbonate ions (HCO3-)

What is the equation for forming hydrogencarbonate ions?

• CO2 + H2O → H2CO3 → H^+ + HCO3

What is the name of H2CO3

• Carbonic acid

What is the name of the catalyst used to form carbonic acid

• Carbonic anhydrase

Describe the formation of hydrogen carbonate ions, haemoglobinic acid at respiring tissue?

• At respiring tissue, carbon dioxide concentration is high which means that it diffuses into red blood cells

• The carbon dioxide then reacts with water in the cell with carbonic anhydrase to form carbonic acid

• The carbonic acid then readily dissociated into H+ ions and hydrogen carbonate ions

• The hydrogen carbonate then leaves the red blood cell and moves in the plasma

• This causes a chlorine shift to occur and chloride ions to move into the red blood cell

• In the haemoglobin the oxygen dissociates due to a low partial pressure of oxygen and leaves the cell

• This leaves the haem group free

• The Haemoglobin and the H+ ions then associate with haemoglobin to form haemoglobinic acid

Explain what is a chlorine shift and why is it important?

• It is when chloride ions move into the red blood cells due to hydrogen carbonate ions leaving the red blood cell

• It important as it maintains the charge of the red blood cell to stay neutral

Why the formation of Haemoglobinic acid important?

• Because it prevents the building up of H+ ions in the red blood cell which causes the contents to become very acidic. Therefore acting as a pH buffer to maintain a pH of 7.4 at all times

What is meant by the Bohr effect?

• It is the effect that a greater conc of CO2 has on haemoglobin which causes it to dissociate from more oxygen

Describe what the Bohr effect is?

• The Bohr effect is when there is a higher concentration of CO2 in tissue, which leads to the formation of more H+ ions from the dissociation of carbonic acid

• These H+ ions lead to an a reduction in pH making the cytoplasm more acidic - about 7.2 instead of 7.4

• This changes the structure of the haemoglobin and therefore reduces the affinity of the haemoglobin for oxygen and therefore results in oxygen dissociating from haemoglobin more readily at areas where CO2 concentration is higher

• This causes the haemoglobin affinity curve to move down and to the right

What doe sthe bohr effect explain?

• It explains why when there is a lot of CO2 the affinity of haemoglobin for O2 is lower

What are factors that affect dissociation of oxygen?

• Blood temperature

• pH

• Carbon dioxide concentration

How does temperature affect dissociation of oxygen?

• As you increase the blood temperature

• The shape of haemoglobin changes (conformational change) which leads to a reduction of haemoglobin affinity for oxygen

• Therefore more oxygen is delivered to warmed-up tissue

how does pH affect dissociation of oxygen?

• As you lower the pH of the blood, which may be causes from lactic acid or carbonic acid dissociating

• It causes a conformational change and reduces the affinity of haemoglobin for oxygen

• This means that more oxygen is delivered to areas of the body that are more acidic as they are respiring more

What is the concentration of carbon dioxide affect dissociation of oxygen?

• The higher the CO2 concentration in tissue

• The lower the affinity of haemoglobin for oxygen which is due to the Bohr effect

• This therefore means that the tissue which are respiring more receive more oxygen for respiration