Country: United States
Date: December 2006
How does hemoglobin carry oxygen to cells?
Hemoglobin is a metalloprotein (a protein that contains a metal) which is
very important in oxygen transport. Hemoglobin has four parts (subunits) to
it, each with an iron atom bound. Each iron atom can be oxidized by binding
a molecule of oxygen, and each time this happens the protein changes shape
so that it can bind more oxygen molecules more effectively, this is known as
If the hemoglobin is an environment that is low in oxygen it won't bind much
oxygen, but as a result of cooperativity if the hemoglobin is around a lot
of oxygen it will bind the oxygen very well. This way hemoglobin is used by
the body to take oxygen from the lungs (where there is a lot of it) to
places like our muscles (which are low in oxygen).
Stanford Department of Chemistry
Each hemoglobin molecule contains four iron atoms each of which can
reversibly bind an Oxygen molecule.
Ron Baker, Ph.D
Here's the basics of how our red blood cells function in taking oxygen
from our lungs to our functioning tissues.
To start, it is important for the cells in our body to have a constant
supply of oxygen. These cells need oxygen to make energy in the form
of ATP. The cells make this energy mainly by breaking down sugars
(glucose is the sugar most preferred by our cells) and extracting the
energy from it. This usable energy is stored within the chemical
bonds of a molecule called ATP. Without oxygen our cells can make
only a fraction of the ATP that we need. Without ATP our cells cannot
carry out their functions and cannot survive, they quickly become
damaged and die. If this happens, WE become tired, sick and aren't
able to survive. So we really need a good way to assure that the
tissues in our body get the oxygen that it needs!
More about ATP and it's importance later.
So now we know how important oxygen is to our bodies - but there is
one problem - oxygen does not dissolve in our blood very well. This
is where hemoglobin comes in.
Red Blood cells (also known as erythrocytes) serve many functions in
our body. One of the main jobs of the erythrocyte is to carry oxygen
to our working tissues. Erythrocytes are the red blood cells that are
dissolved in our blood.
Erythrocytes contain a protein called hemoglobin. Hemoglobin contains
four "pockets" if you can use your imagination. In the middle of each
pocket is a molecule of iron. It is this iron that is responsible for
the oxygen carrying capabilities of hemoglobin and our red blood
In our lungs, the concentration of oxygen is high. Oxygen enters the
red blood cells and binds to the iron within the hemoglobin molecules.
It is the binding of oxygen to the iron inside hemoglobin that
enables our blood to carry enough oxygen to our cells so they can keep
From our lungs, this oxygen rich blood goes to our hearts, where it is
pumped out into our bodies through the biggest artery in our body, the
aorta. Our aorta branches into many other arteries that deliver this
blood, which contains all of that fresh oxygen bound to its hemoglobin
- to our brain, muscles, organs and other tissues. Once it reaches
these working tissues, it drops off some if it's oxygen so these cells
can use it to make ATP. Because the oxygen concentration is low at
these places, it can come off of the hemoglobin. It will then pick up
carbon dioxide - which is produced by working tissues as a waste
product of making ATP - and once again return to our lungs where it
will drop off the carbon dioxide (which we will breath out) and pick
up some more fresh oxygen (which we breath in).
Hopefully this helps. These are very cool and complex processes.
There are many other factors to think about when it comes to all of
these processes that I described above. I hope you find them
interesting and this raises more questions and furthers your study of
Physiology, science and medicine can be very fascinating!
Stephen A. Sardino Jr.
MS - III
Pennsylvania State University - College of Medicine
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Update: June 2012