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How Does Carbon Dioxide Bind to Hemoglobin?


To bind with hemoglobin, carbon dioxide participates in two biochemical effects, which ultimately create a situation wherein hemoglobin offloads bonded oxygen and then takes on carbon dioxide. Hemoglobin is a protein embedded in red blood cells, which delivers oxygen to tissues and carbon dioxide to the lungs. It creates bonds for transportation purposes, but breaks those bonds when it reaches its delivery site.

The Haldane Effect: Regulating Transport

In a general way, hemoglobin can be thought of as a delivery truck with a specific loading capacity. Filling that capacity with oxygen leaves less room for carbon dioxide, and vice versa. The body’s biochemistry adds further complexity to this model, by increasing or reducing hemoglobin’s carrying affinities due to the oxygenation of a particular region. Regions with high oxygenation result in a reduced affinity for carrying carbon dioxide. Alternatively, regions with low oxygenation result in an increased affinity for carrying carbon dioxide. Known as the Haldane Effect, these altering affinities are a vital component in delivering oxygen to starved tissues and removing carbon dioxide from the body.

The Bohr Effect: An Inverse Relationship

In addition to the Haldane effect, hemoglobin’s oxygen binding affinity is further influenced by an additional factor. It has an inverse relationship to both pH and the concentration of carbon dioxide, which is known as the Bohr Effect. Increases in either partial pressures or acidity will lead to oxygen discharging. Afterward, the affinity for removing carbon dioxide increases, and the red blood cells make their return trip.


Oxygen bonds directly to the protein’s iron atoms. However, carbon dioxide requires more complicated bonding methods. By dissolving in deoxygenated blood, carbon dioxide participates in a chemical reaction, binding with hemoglobin to form a special compound called carbaminohemoglobin. This allows the transportation of carbon dioxide back to the lungs, and subsequent expulsion from the system.



Davidson College

Harvard University
Hemoglobin Overview

The Japanese Journal of Physiology; Tyuma l
The Bohr effect and the Haldane effect in human hemoglobin
1984; Volume: 34; No: 2; Pages: 205-216

East Tennessee State University
The Hemoglobin Page

Austin Community College
The Bohr Effect

Glossary of Terms

Biochemical Reaction: the process in which two or more molecules (reactants) interact, usually with the help of an enzyme, and produce a product; also, a biochemical reaction may involve the breakdown of a single reactant and the production of multiple products.
San Diego State University

Carbaminohemoglobin: a combination of carbon dioxide and hemoglobin, CO2HHb, being one of the forms in which carbon dioxide exists in the blood.
Dorland’s Medical Dictionary for Health Consumers

Hemoglobin: a protein in red blood cells that carries oxygen. A blood test can tell how much hemoglobin you have in your blood.
Medline Plus

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