Dissociation Curves

Question 1

Haemoglobin

Answer 1

• Quaternary structure made of 4 subunits (2a and 2ß)
• Each subunit has a polypeptide chain and a haem group (Fe2+)
• Fe+ has affinity (attraction to bind) for oxygen
• 4 molecules of O2 per haemoglobin
• Binds/ associates with O2 in lungs and unbinds/ dissociates in tissues
• Ability to take in and release depends on partial pressure (conc) of O2 in surrounding tissues

Question 2

Cooperative binding

Answer 2

• Haem group at the centre of Hb so difficult for O2 to bind- low saturation with O2 at low partial pressures at lower conc of CO2
• As ppO2 increases, diffusion gradient increases and 1st O2 molecule binds with 1 group
• Changes shape of Hb molecules making it easier for 2nd to attach
• Same for 2nd and 3rd but no shape change for 3rd
• Difficult of Hb to be 100% saturated as high increase in ppO2 needed for 4th O2

Question 3

Effect of partial pressures of oxygen

Answer 3

• At high pp, Hb associates with O2 to form oxyhaemoglobin as higher affinity of Hb for O2
  
  • Lungs
• At low pp, affinity of Hb for O2 decreases and Hb releases O2 in tissue with low levels of O2
  
  • Respiring tissues

Question 4

Dissociation curve

Answer 4

• Sigmoidal curve and not linear
• Small change in pp = large change in % saturation
  - Small increase in pp results in a large increase in % saturation
• More efficient unloading of oxygen to respiring tissue
• Saturation reached at lower partial pressures

Question 5

Linear shape

Answer 5

• At low pp, affinity for O2 would be too high and O2 would not be released in tissues
• At high pp, affinity for O2 would be too low and O2 would be readily released and not reach tissues

Question 6

What causes a decrease in ppO2?

Answer 6

• (Vigorous) exercise
• High levels of aerobic respiration
• Oxygen used by muscle cells

Question 7

Llama

Answer 7

• Lives at high altitudes where oxygen is scarce (low ppO2)
• Higher number of RBC and more Hb at high altitudes
• Curve shifts to left
• Curve shows Hb has higher affinity for O2
• Hb can pick up become saturated with O2 more easily at lower pp
• Small change in pp results in large change in % saturation

Question 8

Lugworm

Answer 8

• Lives head-down in burrow in low O2 environment by sea-shore
• Low metabolic rate and pumps seawater through burrow
• Gives access to limited O2
• Curve shift to left
• High affinity for O2 so picks up O2 and low partial pressure
• Releases in very low pp
• Small change in pp = large change in % saturation

Question 9

Foetus

Answer 9

• Hb in foetus must absorb more O2 from maternal Hb in placenta
• Exchange by diffusion so placenta not in contact
• Hb differs in 2 polypeptide chains
• Curve shift to left
• Hb has higher affinity for O2 than maternal Hb at all oxygen pp
• More saturated than maternal Hb at all oxygen pp
• Oxygen passes from maternal to foetal blood

Question 10

Myoglobin

Answer 10

• Oxygen binding protein in skeletal muscles
• Acts as an intracellular oxygen store
• High affinity for O2 at low pp so saturated at low pp
• Used when muscle exercising heavily

Question 11

How is oxygen released from Hb?

Answer 11

• Accumulation/ high concentration of carbonic acid
• Causes fall in pH and increases acidity
• Releases O2 from oxyhaemoglobin

Question 12

Lower pH/ increased acidity/ increased CO2

Answer 12

• Bohr effect
• Higher rate of respiration so more CO2 produced (higher conc)
• Increased concentration of carbonic acid
• Increased concentration of H+ ions which reduce pH and increase acidity
• Decrease in affinity of Hb for O2 so more oxygen released and more readily from oxyHb

Question 13

Benefits of curve shift to right (mouse or acidity)

Answer 13

• Lower affinity of Hb for O2
• More O2 released and dissociates more readily
• Can be used in aerobic respiration by muscle cells