- Being heterozygous (one having one gene for the sickle-cell anemia) has more resistance to malaria which is why it is evolutionarily found to be more prevalent in areas where malaria is a prevalent disease. 
- When infected with malaria, the cells sickle due to a lower pH in the blood causing an increasing likelihood of the S hemoglobin cells to sickle. 
- In early stages of infection, the parasitized cells sickle and disrupt the parasite and the spleen can remove the infected erythrocytes. 
- In later stages in infection, the parasitized erythrocytes disrupt the parasite mechanically because of their sickle shape. 
- This makes the population more heterozygous for the S hemoglobin gene for sickle-cell anemia. 


Sickle-Cell Anemia and Malaria

- Administering hydroxyurea has been determined to be an effective treatment for sickle-cell anemia.
- It increases the fraction of cells that have fetal hemoglobin which has a separate subunit gamma rather than the defective beta chain that is found in mutated hemoglobin blood cells. 
- Still little is know of this mechanism however. 

Treating sickle-cell anemia

- Inheritable blood disease 
- Homozygous (or those with both genes) people with hemoglobin S have sickle-cell disease. 
- Heterozygous individuals usually live healthy lives but have lower erythrocyte count.
- The cells form a sickle shape because of one amino acid is mutated (Glu -> Val)
- This amino acid change allows the hemoglobin to bind to other hemoglobin at the binding pocket causing a mass sickle shape of the blood cells. 
- It is difficult for cells to pass through capillaries and deliver oxygen which can cause tissue death. 


Grand Valley State University

There are many diseases associated with mutations in hemoglobin.
- Sickle-cell anemia 
- Polycythemia 
- Cyanosis
- Hemolytic anemia

Mutations in hemoglobin

Voet, D., Voet, J. G., & Pratt, C. W. (2013). Chapter 7: Protein Function: Myoglobin and Hemoglobin, Muscle Contractions, and Antibodies. In Fundamentals of biochemistry: Life at the molecular level (4th ed., pp. 176-216). Hoboken, NJ: Wiley. Retrieved February 21, 2021, from archive.org.

Fundamental of biochemistry: Life of the molecular level 4th edition: Chapter 7

- Hemoglobins are mutated in that they have less affinity for oxygen and are degraded by erythrocytes (red blood cells) 
- Causes a decrease in the red blood cell count and thus decrease oxygen flow to the tissues.


Hemolytic anemia

- Mutations of the oxygen binding site of hemoglobin causing oxidation of Iron II to Iron III 
- The cooperativity of the binding pockets are decreased in hemoglobin. 
- People exhibit a bluish skin because this mutation creates methemoglobin. 


Cyanosis 

- Mutations found to increase oxygen affinity to the hemoglobin.
- This causes increased amounts of red blood cells to compensate for less oxygen being released to the tissues. 

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