[7.1] haemoglobin

Question 1

describe the structure of haemoglobin

Answer 1

• quaternary structure
• multiple polypeptide chains
• additional non-protein molecule
  > haem molecule with iron atom

Question 2

draw a simplified diagram of haemoglobin

Answer 2

• 4 × ‘haem’ groups (including Fe)
• 4 × ‘globin’ polypeptide chains (2× alpha, 2× beta)
• 4 × binding sites for O₂

Question 3

what is the equation for when oxygen reacts with haemoglobin?

Answer 3

oxygen + haemoglobin ⇌ oxyhaemoglobin

Question 4

what are some “adaptations” of RBC and haemoglobin?

Answer 4

• haemoglobin’s 4 binding sites don’t all have to be filled: can carry none or 1 or 2 or 3 or 4 oxygens
• found in massive quantities in RBC
• no nucleus in RBC so more space for haemoglobin

Question 5

what is cooperative binding?

Answer 5

• when oxygen 1 binds, the rest of the hgb molecule changes shape which makes the other binding sites more accessible
• therefore, it is most difficult to bind oxygen 1
• oxygen 2 and 3 are easy to bind because of the change in shape
• oxygen 4 is hard to bind because there is a lower probability of oxygen binding at the right place since there is only 1 spot left now

Question 6

what is the process by which haemoglobin binds with oxygen?

Answer 6

• loading, or associating
• in humans this takes place in the lungs

Question 7

what is the process by which haemoglobin releases its oxygen?

Answer 7

• unloading, or dissociating
• in humans this takes place in the tissues

Question 8

haemoglobin and affinity

Answer 8

• hgb with high affinity for oxygen take up oxygen more easily, but release it less easily
• hgb with low affinity for oxygen take up oxygen less easily, but release it more easily

Question 9

what is the role of haemoglobin and what must it be to be efficient in this role?

Answer 9

• role is to transport oxygen
• it must readily associate with oxygen at the surface where gas exchange takes place (lungs)
• also readily dissociate from oxygen at tissues requiring it

Question 10

describe how the conditions at the gas exchange surface affect oxygen

Answer 10

• high oxygen concentration
• low carbon dioxide concentration
• high affinity of haemoglobin for oxygen
• results in oxygen being associated

Question 11

describe how the conditions at the respiring tissues affect oxygen

Answer 11

• low oxygen concentration
• high carbon dioxide concentration
• low affinity of haemoglobin for oxygen
• results in oxygen being dissociated

Question 12

how and why are there different haemoglobins?

Answer 12

• each species produces a hgb with a slightly different amino acid sequence so it has a slightly different tertiary and quaternary structure and hence different oxygen binding properties
• depending on its structure, hgb molecules range from having high affinity for oxygen to low affinity for oxygen