Hey there! Sign in to join this conversationNew here? Join for free

A Level Biology help! How does low partial pressure lead to high affinity? Watch

    • Community Assistant
    • Thread Starter
    Offline

    18
    ReputationRep:
    For example, how does low partial pressure of O2 cause high affinity of haemoglobin for O2? I mean, is there even a causal relationship, or does it link to carbon dioxide?

    Explanations very much appreciated!
    Offline

    10
    ReputationRep:
    (Original post by honour)
    For example, how does low partial pressure of O2 cause high affinity of haemoglobin for O2? I mean, is there even a causal relationship, or does it link to carbon dioxide?

    Explanations very much appreciated!
    So affinity depends on a number of things, the concentration of 2,3-DPG (a product of metabolism), the pH (and therefore CO2 by association), and the amount of oxygen bound. The type of haemoglobin also has an affect but I won't go into that.

    So the partial pressure of O2 doesn't change the affinity of haemoglobin. In the tissues, where the pO2 is low, the pCO2 and 2,3 DPG is high, which lowers the affinity of haemoglobin so that it releases its oxygen. In the lungs where pCO2 and 2,3 DPG are low, the affinity is increased to allow the haemoglobin to get as much oxygen bound as possible. Also, if you look at it in terms of correlation instead of causation, the affinity for oxygen actually increases as pO2 increases, this is because as oxygen binds, it loosens up the haemoglobin structure, which allows more oxygen to bind more easily.

    So actually, affinity increases as you increase pO2, hence why a oxyhaemogobin dissociation curve is sigmoid shaped.

    Does that all make sense?
    Offline

    4
    ReputationRep:
    organisms that live in an environment where there is a low po2 (low concentration of oxygen) have haemoglobin that has a higher affinity to oxygen, so oxygen loads more readily on to their haemoglobin.
    • Community Assistant
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by AortaStudyMore)
    So affinity depends on a number of things, the concentration of 2,3-DPG (a product of metabolism), the pH (and therefore CO2 by association), and the amount of oxygen bound. The type of haemoglobin also has an affect but I won't go into that.

    So the partial pressure of O2 doesn't change the affinity of haemoglobin. In the tissues, where the pO2 is low, the pCO2 and 2,3 DPG is high, which lowers the affinity of haemoglobin so that it releases its oxygen. In the lungs where pCO2 and 2,3 DPG are low, the affinity is increased to allow the haemoglobin to get as much oxygen bound as possible. Also, if you look at it in terms of correlation instead of causation, the affinity for oxygen actually increases as pO2 increases, this is because as oxygen binds, it loosens up the haemoglobin structure, which allows more oxygen to bind more easily.

    So actually, affinity increases as you increase pO2, hence why a oxyhaemogobin dissociation curve is sigmoid shaped.

    Does that all make sense?
    Perfect, you've explained very well. After reading this over a few times, it made a lot of sense. Thanks dude, you're fantastic!

    Spoiler:
    Show

    I love your username too, very original! :thumbsup:
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Did TEF Bronze Award affect your UCAS choices?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.