Hemoglobin Molecule

What is Hemoglobin?

Hemoglobin is a protein that you can find in your blood. Specifically, it is in the red blood cells (RBC), and it contains iron. The iron in hemoglobin is what binds to oxygen so that your RBCs have oxygen to transport to your body’s cells.

All of your body’s cells need oxygen, so hemoglobin is a very important protein in your body.

Hemoglobin Molecule

The hemoglobin molecule is what makes your blood a bright red colour because of the oxygen. Blood that is not full of oxygen is more of a deep purple colour instead of bright red.

When hemoglobin isn’t working properly, that is when you can get problems where your RBCs aren’t working properly, and your body doesn’t get enough oxygen.

There are a few reasons why you may not have enough hemoglobin. As a result of low hemoglobin, your tissues may not be getting as much oxygen as they should. This is when you can have anemia. Iron deficiency anemia (IDA) is an example of this scenario. Iron is essential for making hemoglobin, and low levels of this mineral can turn into IDA.

Hemoglobin Structure

Each hemoglobin molecule has four chains. Two of them are called alpha chains and the other two are called beta chains. These chains are built together in a tetrahedron shape.

Each chain has a ring-like heme structure, and each heme structure has an iron atom in it. This iron is what binds to oxygen to let the red blood cells transport oxygen throughout your body. A single RBC has around 270 million hemoglobin molecules.

Function of Hemoglobin

Hemoglobin transports oxygen throughout your body. It also helps transport carbon dioxide back to your lungs so that you can breathe it out. So, whenever you take a breath in and out, hemoglobin is helping make sure that your body gets the oxygen it needs and takes out the carbon dioxide that it doesn’t need.

Hemoglobin also strongly binds to carbon monoxide, even better than it binds to oxygen. This means that if you have carbon monoxide poisoning, you won’t be able to get oxygen to your body’s cells as the hemoglobin will bind to carbon monoxide instead of oxygen. That is why carbon monoxide is so dangerous and why we need carbon monoxide detectors in our homes.  

How Many Molecules of Oxygen Can Hemoglobin Carry?

As mentioned before each hemoglobin molecule has four chains. So, it has four heme structures, and therefore, four molecules of iron. Each iron binds one molecule of oxygen.

This means that each hemoglobin molecule can carry four molecules of oxygen

Hemoglobin Levels

It is important to check how much hemoglobin you have in your blood to make sure you are not deficient. You can test the amount of hemoglobin with a blood test. The normal range for hemoglobin is around 120 g/L to 180 g/L, but the normal range can vary depending on your age and sex.  

You don’t want to have too little or too much hemoglobin in your blood. If you don’t have enough hemoglobin in your blood, then you may have a low RBC count. This can be caused by many things like iron deficiency anemia (IDA).

IDA is a condition where you don’t have enough iron, which is important for making hemoglobin. Consequently, you would have low levels of hemoglobin as well.

If you want to donate blood, you need to check your hemoglobin levels first to make sure they are high enough. You wouldn’t want to have low hemoglobin and then donate blood and have even less.

Here are some causes of low hemoglobin levels:

  • Menstruation
  • Iron deficiency
  • Vitamin B-12 or folate deficiency
  • Kidney disease
  • Liver disease

If you have too much hemoglobin, that can be bad too. In some cases, this can occur because you are making too many RBCs. Another reason can be because you have too much iron in your body. Sometimes it can just be a natural occurrence. If there is a problem with too much iron, you would want to treat to make sure that doesn’t cause problems.

Here are some more causes of high hemoglobin levels:

  • Polycythemia vera (bone marrow makes too many RBCs)
  • Dehydration
  • Lung disease
  • High altitudes (this is a normal response)

If you feel tired or unwell, you can ask your doctor to do a blood test and check your hemoglobin levels to see if you have anemia. If you have iron deficiency anemia, you may have low hemoglobin and low iron levels in your blood. Speak to your doctor about iron supplements to increase your iron levels.


Hemoglobin is a very important molecule in your body. Your body always needs oxygen and always needs to get rid of carbon dioxide. The function of hemoglobin is to transport oxygen around your body.

It’s important that you have enough hemoglobin for optimal health. If you think you may have low or even high hemoglobin levels make sure to talk to your doctor. You healthcare practitioner can do a blood test and recommend next steps depending on the results.


Britannica: Hemoglobin
Protein Data Bank: Molecule of the Month: Hemoglobin
National Library of Medicine: Structure-function relations of human hemoglobin
McGill Office for Science and Society: Under the Microscope: Blood
Mayo Clinic: Hemoglobin test
Canadian Blood Services: What you need to know about hemoglobin, hemochromatosis, iron and anemia

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