3.4 Oxygen dissociation curve

haemoglobin molecule

• quaternary structure as it has 4 polypeptide chains

• 4 haem groups which contain an iron ion

• has 4 oxygen binding sites

• oxygen binds to haemoglobin to form oxyhemoglobin

• binding of oxygen is reversible

• haemoglobin loads (associates with) oxygen in the lungs

• it unloads (dissociates from oxygen) in respiring tissues

tertiary structure of haemoglobin (protein)

• tertiary structure determined by primary structure

• in addition, Ph can affect the tertiary structure, temperature above 40 degrees and another nmoeldule binding to it can affect this

haemoglobin oxygen dissociaton curve

• haemoglobin in a low partial pressure of oxygen (pp = concentration of a gas) has a low saturation - high pp = haemoglobin saturation is high - when haemoglobin in lungs it will load oxygen onto it

• at 50 % saturation on average haemoglobin in your blood had 2 red blood cells binded to them

• relatively small change/ curve lower on the graph - initially quite hard for oxygen to bind - small increase can make it easier for the 2nd oxygen to bind onto the haemoglobin

explain the shape of the oxygen dissociation curve

• (at low partial pressures of oxygen , binding sites are partially covered)

• first oxygen binds to the haemoglobin

• tertiary/quaternary structure changes

• next binding site more exposed

• making it easier for the next oxygen molecule to bind

• that’s why small curve at the bottom of the graph but eventually gets easier

• call this cooperative binding

• flattens off at the top as:

  • almost all haemoglobin molecules are saturated with oxygen

  • the chance of an oxygen molecule colliding

different haemoglobin molecules

• have different primary structure therefore different tertiary/ quaternary structure

• different affinity for oxygen

lugworms oxygen dissociation curve in comparison to human

• higher affinity for oxygen - lower partial pressure it has a higher saturation for haemoglobin with oxygen

• advantage - curve to the left, haemoglobin more saturated at lower partial pressure - higher affinity w oxygen

• adv - better at loading oxygen on haemoglobin from the water in its burrow/ air in lungs for llama

• therefore good in environments with low oxygen concentrations

advantage of mouse haemoglobin

• lower affinity as it had less saturated oxygen at lower partial pressures (curve is to the right) - don’t really see as much of a difference at higher partial pressures

• unload it more easily as the advantage - unloads oxygen more easily to repairing cells

• more oxygen for aerobic respiration

• good for very active organisms with a high metabolic rate

use the graph to explain why llamas are better adapted to live in high mountains than horses

• llama haemoglobin has a higher affinity for oxygen than horse haemoglobin - making oxygen able to associate/ dissociate more easily

• from air in the lungs

• llama haemoglobin has a higher saturation of oxygen at lower partial pressures

Bohr shift

higher concentration of CO2 in the respiring muscles than in the lungs

• effect of higher co2 concentrations on human haemoglobin affinity for oxygen

• what is the advantage of this -

• human haemoglobin in different conditions

• higher co2 concentrations effect on body

• curve to the left, low partial pressures of co2 in the lungs 3kpa

• curve to the right, higher partial pressure of co2 in respiring tissues

what does higher partial pressure of CO2 in respiring tissues mean for the affinity of oxygen and haemoglobin

• lower affinity for oxygen

• advantage - oxygen unloaded more easily - cells have more o2 for aerobic respiration

• what causes this effect?

• higher amounts of co2 reduce the ph of the blood - carbonic acid increase lowering the ph making blood more acidic

explain Bohr effect

• higher co2 concentrations in respiring tissues

• lower ph in respiring tissues

• haemoglobin has a lower saturation with oxygen (at specific partial pressures of o2)

• haemoglobin has a lower affinity with oxygen

• haemoglobin unloads more easily

• more o2 for oxygen