Haemoglobin

Question 1

Explain the adaptations of a red blood cell (GCSE)

Answer 1

• Biconcave shape - larger SA, increasing the rate of diffusion
• No organelles - carry more haemoglobin
• Flexible - they can fit through narrow capillaries

Question 2

Describe the structure of haemoglobin

Answer 2

• Haemoglobin is a globular protein
  • The primary structure is the sequence of amino acids bonded together with peptide bonds
  • The polypeptide chains coil into an a-helix shape due to hydrogen bonding.
  This is the secondary structure
  • The tertiary structure is the specific 3D shape of the haemoglobin, enabling it to carry oxygen. The tertiary structure is caused by hydrogen and ionic bonds between the R groups of the amino acids
  • Haemoglobin has a quaternary structure as it is made from four polypeptide chains.
  • Each chain includes a haem group containing a ferrous ion which can bind to oxygen

Question 3

Define association

Answer 3

Tissues where gas exchange takes place

Question 4

Define disassociation

Answer 4

Tissues where respiration takes place

Question 5

Describe the function of haemoglobin using the word associate and disassociate

Answer 5

• Haemoglobin associates with oxygen in tissues where there is a high partial pressure of oxygen to form oxyhemoglobin
• Oxyhemoglobin dissociates with oxygen in tissues where there is a low partial pressure of oxygen to enable oxygen to diffuse into the cells to be used for aerobic respiration

Question 6

Describe what is meant by partial pressure

Answer 6

Partial pressure is the pressure exerted by one of the gases within a mixture

Question 7

What happens to the partial pressure as you increase the concentration

Answer 7

Increases

Question 8

Why is the partial pressure of oxygen lower in the tissues compared to the alveoli?

Answer 8

The tissues use up oxygen during anaerobic respiration, therefore the concentration of oxygen in the tissues decreases

Question 9

Why is the partial pressure of carbon dioxide higher in the blood entering the lungs compared to the blood leaving the lungs?

Answer 9

The extra carbon dioxide produced in respiration leaves the body during exhalation, so the blood leaving the lungs has a lower concentration of carbon dioxide

Question 10

Why does % saturation increase as pO2 increases

Answer 10

Oxygen diffuses into haemoglobin. So as we increase p02, the concentration gradient increases. The rate of diffusion increases

Question 11

Why is it more likely that oxygen disassociates from haemoglobin at the tissues

Answer 11

• In the tissues, there is a low partial pressure of oxygen
• There is more likely to be a concentration gradient out of the haemoglobin as oxygen is used by the respiring cells in the ossues
The haem groups are in the centre of the haemoglobin as they are not bound to oxygen
As it ls harder for oxygen to bind due to the greater diffusion distance, oxygen is more likely to dissociate than assoclate

Question 12

Why is it more likely that haemoglobin associates with oxygen in the lungs

Answer 12

In the lungs, there is a high partlal pressure of oxygen
• There is a steep concentration gradient into the haeroglobin
• Oxygen is more likely to diffuse into the haemoglobin and bind to a haem group
• The shape of the haemoglobin changes exposing additional haem groups
• It is therefore more likely for oxygen to assoclate than dissociate

Question 13


Describe the role of haemoglobin in supplying oxygen to the tissues of the body.

Answer 13

1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin Ignore ref. to ‘positive cooperativity’ unqualified
   Ignore ref. to named bonds
   Accept conformational shift caused
2. Creates/leads to / uncovers second / another binding site
   OR
   Uncovers another iron / Fe/haem group to bind to;
   Reject ref. to active site

Question 14

Describe and explain what happens as po2 increases up to the tissue

Answer 14

• In the tissues, there is a low partial pressure of oxygen
  There is more likely to be a concentration gradient out of the haemoglobin
• The haem groups are in the centre of the haemoglobin as they are not bound to oxygen
• As it is harder for oxygen to bind due to the greater diffusion distance, oxygen is more likely to dissociate than associate

Question 15

Describe and explain what happens as po2 increases up to the lungs line

Answer 15

• In the lungs, there is a high partial pressure of oxygen There is a steep concentration gradient into the haemoglobin
• Oxygen is more likely to diffuse into the haemoglobin and bind to a haem group
• The shape of the haemoglobin changes exposing additional haem groups
• It is therefore more likely for oxygen to associate than dissociate

Question 16

Describe what is meant by affinity

Answer 16

Affinity is a property where the tertiary determines how much easy it is for oxygen to associate

Question 17

The higher the affinity..

Answer 17

The more readily oxygen associates

Question 18

Haemoglobin with higher affinity…

Answer 18

• Haemoglobin with higher affinity has greater ability to associate with oxygen and less ability to dissociate from oxygen.

Question 19

Haemoglobin with lower affinity…

Answer 19

• Haemoglobin with lower affinity has greater ability to dissociate from oxygen and less ability to associate with oxygen.

Question 20

Why is the Bohr shift advantageous in exercise? Use the key word affinity and dissociate

Answer 20

• When the Bohr shift occurs, the affinity of haemoglobin for oxygen decreases.
• This means that oxygen more readily dissociates from haemoglobin.
• Therefore, more oxygen diffuses from red blood cells into the respiring tissues.
• Rate of aerobic respiration increases, providing more ATP for more muscle contraction in exercise.