Oxygen dissociation curve explanation

Hi I’m in dire need of help!
Please could somebody explain the oxygen dissociation curve in the simplest way possible. So from what I have read the curve is sigmoidal because of cooperative binding, so at lower partial pressures it’s more difficult for oxygen to bind to haemoglobin due to its tense state but after the first o2 binds it converts to a relaxed state. I just don’t understand how that relates to the graph though, is the graph representative of a singular haemoglobin molecule or all haemoglobin molecules? AARGHHH, please help my alevel grade is depending on you guys🥲🙏

Reply 1

Nitrotoluene

Original post by Basilica

Hello Basilica!
The oxygen dissociation curve is simply a plot of how much oxygen is bound to hemoglobin (Hb) at different oxygen partial pressures (pO2). The shape of curve is an S.
pO2, or partial pressure of oxygen measures how much oxygen is in the blood.
Basically:
At low pO2, oxygen has a hard time binding to hemoglobin because the hemoglobin is stiff and tight. It’s just not loose enough to allow the oxygen in there.
But when pO2 increases, following molecular binding of the 1st O2 on the hemoglobin molecule, this induces a conformational change that releases the other O2 molecule from its bond. The first of those bonds, changes the shape a little bit, so that it’s easier for more oxygen to jump on.
Each time an oxygen joins the party, the hemoglobin becomes more relaxed, and it’s really easy for another oxygen to bind. This is why the curve rises steeply as pO2 rises.
The curve plateaus when pO2 is high enough that almost the entire pool of hemoglobin is saturated with oxygen.
As a reminder, this graph depicts what occurs to a cluster of hemoglobin molecules (not just a single one).
It’s like folks getting on a bus. At low bus capacity (low pO2) it’s a hassle getting in because everyone is clustered at the door. But get a few people on (the first oxygen bonds), and there’s more space, so you find it easier to get on. And when the bus is "complicated" (high pO2), well you don't get on at all.
Hope that helps clarify the curve a little bit!

Bye, Sandro

(edited 1 month ago)