Transport of oxygen by haemoglobin

cooperative binding

• first oxygen binds to haemoglobin, changing tertiary structure

• this creates/uncovers another binding site

• change in shape (of haemoglobin) allows more oxygen to bind easily

How does partial pressure of oxygen affect oxygen-haemoglobin binding?

1.As partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases

-so oxygen binds tightly to haemoglobin.

2.When partial pressure is low:

-oxygen is released from haemoglobin.

Bohr effect OxyHb graph

When a high carbon Dioxide concentration causes the oxyhemoglobin curve to shift to the right

The affinity for oxygen decreases b/c the acidic carbon dioxide changes the shape of haemoglobin slightly

Bohr effect

1. As partial pressure of carbon dioxide increases, the conditions become acidic due to the increase in H+ ions, causing haemoglobin to change shape.

2. The affinity of haemoglobin for oxygen therefore decreases

3. so oxygen is released from haemoglobin.and so more oxygen can be delivered to cells for respiration

How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?

It is hard for the first oxygen molecule to bind but once it does:

• first oxygen molecule binds to haemoglobin, changing the tertiary structure

• this reveals/uncovers another binding site

• it changes the shape of haemoglobin to make it easier for the second and third oxygen molecules to bind

• known as positive cooperativity.

It is then slightly harder for the fourth oxygen molecule to bind

• because there is a low chance of finding a binding site.

Describe and explain the shape of the curve in

Explain why oxygen binds to haemoglobin in the lungs.

1. Partial pressure of oxygen is high.

2. Low concentration of carbon dioxide in the lungs, so affinity of Hb to oxygen is high.

3. Positive cooperativity

Explain why oxygen is released from haemoglobin in respiring tissues.

1. Partial pressure of oxygen is low

2. High concentration of carbon dioxide in respiring tissues, so affinity of Hb to oxygen decreases.

if oxyhaemoglobin dissociation curve goes towards the left

• haemoglobin has higher affinity for oxygen

• so it releases less oxygen/ uploads more oxygen

• Dissociates oxygen more readily

• it becomes saturated at lower partial pressure

if oxyhaemoglobin dissociation curve shifts to the right

• haemoglobin has a lower affinity for oxygen

• so it unloads/dissociates more oxygen, more readily into cells for respiration

  • therefore greater (rate of ) respiration

• at a particular partial pressure, more oxygen released

Foetal haemoglobin

has higher affinity for oxygen (than adult haemoglobin), even at the same partial pressure

• loads oxygen from mothers haemoglobin/blood

• so more oxygen moves from the mother to the fetus

advantage of replacing fetal haemoglobin with adult haemoglobin

• adult haemoglobin has a lower affinity for oxygen

• so more oxygen is released and delivered to respiring cells

• easier unloading of oxygen for aerobic respiration

how oxygen is loaded, transported and unloaded in the blood

1. haemoglobin has a high affinity for oxygen

2. at high partial pressure: oxygen is uptaken into the lungs

3. at low partial pressure: oxygen is released into respiring cells

   • this is due to higher CO2 conc. (bc respiration)

Figure 1 shows the oxygen dissociation curve for human haemoglobin.

• loading of oxygen at high partial pressure

• in the lungs, haemoglobin has a high affinity for oxygen

• haemoglobin unloads oxygen at low partial pressure

Explain how the shape of a red blood cell allows it to take up a large amount of oxygen in a short time.

1. large SA:V ratio

   • for diffusion

2. thin

   • so oxygen can release all haemoglobin

Explain how oxygen in a red blood cell is made available for respiration in active tissues.

• low pH due to increased CO2

• increased dissociation of oxygen from haemoglobin

• oxygen diffuses from rbc to tissues

What is meant by the term partial pressure?

the measure of concentration of a gas