Sickle cell disease, often called sickle cell anemia, is the result of a mutation in your DNA. Passed on from your parents, it leads to malformation of hemoglobin, the protein in red blood cells. The hemoglobin protein in sickle cell patients has an incorrect amino acid --- a valine in place of glutamic acid.
Sickle Cell Anemia
Sickle cell anemia results from improperly-shaped red blood cells -- shaped like sickles instead of biconcave and smooth --- as the result of improperly-shaped hemoglobin proteins. The sickled cells not only cannot effectively transport oxygen but also tend to get caught on one another in small blood vessels, leading to clots. This causes patients to experience pain and sometimes organ failure, notes PubMed Health.
Cause Of Sickle Cell
The hemoglobin protein that makes up red blood cells is very large. Like all proteins, it is comprised of building block molecules called amino acids, of which there are 20 common varieties. The order in which amino acids bond to one another determines the shape and function of a protein; hundreds of amino acids must assemble in the correct order to produce hemoglobin and other proteins. In sickle cell patients, there is a mistake in one amino acid out of hundreds.
Valine
The incorrect amino acid in hemoglobin is called valine; the correct amino acid is glutamic acid. One of the reasons the mistake is so severe is that valine and glutamic acid have very different side chains. A side chain is a cluster of atoms on an amino acid that determines its properties. Valine has a carbon and hydrogen side chain, while glutamic acid's also includes oxygen and is acidic.
Why This Is A Problem
A protein's function depends upon more than just the identities of the amino acids comprising it; the order of amino acids determines the three-dimensional protein shape, which determines the protein's function. In sickle cell, because there's a valine where a glutamic acid should be, the protein doesn't fold into the right shape, meaning it cannot transport oxygen molecules well and produces misshapen red blood cells, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
References
- PubMed Health: Sickle Cell Anemia
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- Harvard: How Does Sickle Cell Cause Disease?
