Sickle Cell Anemia - Essay Example

Sickle Cell Anemia Sickle cell anemia is a genetic disease which is inherited, and can be passed down several generations through both the parents. The term ‘sickle cell’ comes from the sickle shaped or crescent shaped form of the hemoglobin molecules. This sickling of the cells is caused due to a change in one of the nucleotides of a DNA molecule out of the billion other cells present in the human body. This change may seem minor, but the results are disastrous. A person affected with sickle cell anemia inherits a mutated or recessive allele from both the parents.

Therefore the patient contains faulty hemoglobin in the red blood cells, which causes the cells to become deformed and sickled when oxygen levels in the blood get low. In this sickled form the red blood cells are less efficient in transporting oxygen and are more likely to stick in blood capillaries preventing the blood flow. This mutation causes the shape of the hemoglobin molecule, present in the blood, to change, preventing it from carrying oxygen around the body. Various organs are deprived of the oxygen molecule inhibiting them from performing their basic anabolic and catabolic functions, and hence causing them to wear out.

These sickle shaped hemoglobin molecules cause the blood to become stick and the floe becomes irregular. Under normal conditions, hemoglobin cells are donut shaped, and can flow easily with the blood, in arteries and capillaries. They are flexible and hence can squeeze in and out of capillaries. But sickle shaped hemoglobin molecules are rigid and tend to get stuck in the arteries, causing the blood flow to become restricted. (Bjorklund) Human beings contain 23 chromosomes inside the nucleus of a cell, and these chromosomes contain all the genetic material responsible for their characteristics.

A single unit of DNA is known as a gene. Genes contain the information required to synthesize proteins, and these proteins are accountable for our traits. These genes contain a sequence of nucleotides which dictate the sequence of the corresponding amino acids, that are linked together to form polypeptide chains and hence, proteins. Mutations occur when there is a change in this sequence, and the results could be very harmful as this change in the order of nucleotides, could change the structure and function of a protein completely.

There are many types of mutations and they could either be beneficial or harmful. This type of mutation is an example of a point mutation or a missense mutation, and is obviously extremely harmful, if the gene occurs in a homozygotic form. It occurs in the beta globin gene (HBB) which is present in the 11th chromosome. The HBB gene is responsible for normal blood production. The point mutation causes the beta hemoglobin molecule to convert the GAG codon into a GUG codon by transcription i.e. it encodes the amino acid valine rather than the seventh amino acid, glutamic acid.

Valine is hydrophobic (water hating) causing the hemoglobin molecule to bend inwards, causing it to become sickle shaped. There are no other changes in the structure. (Eldra Solomon) Sequence for Normal Hemoglobin ATG GTG CAC CTG ACT CCT GAG GAG AAG TCT GCC GTT ACT START Val His Leu Thr Pro Glu Glu Lys Ser Ala Val Thr Sequence for Sickle Cell Hemoglobin ATG GTG CAC CTG ACT CCT GTG GAG AAG TCT GCC GTT ACT START Val His Leu Thr Pro Val Glu Lys Ser Ala Val Thr This sickle cell gene mutation is mostly common in African people or people from the Middle East.

Not everyone carrying the gene could be affected severely by sickle cell anemia. Each gene has different versions called alleles. A person carrying one allele for sickle cells, but one for normal cells is said to be heterozygous or a carrier of sickling hemoglobin. The problems of sickling, clotting and blockage could be minor and controlled if certain precautions are taken. In most cases, carriers only show symptoms of sickle cell disease if they deprived of oxygen, such as during extreme exertion or going to areas of high altitude where the air is thinner.

People who contain both the alleles for sickling are called homozygous and most of their hemoglobin molecules are sickle shaped. The allele which is responsible for sickle cell disease is an autosomal recessive gene, which means that it shows all its characteristics if both the alleles are present(John David Rainer). A recessive gene is unable to show it’s characteristics in the presence of a dominant allele, in this case, the dominant allele is the normal hemoglobin gene. But sickle cell disease is partially recessive, which means that when it is present with a dominant allele (in a heterozygous form), it will still show some of its traits under specific circumstances.

A person can become homozygous for the gene if it receives the sickle cell allele from both the parents. That is if both parents are carrying the sickle cell allele, there is a 25% chance that the child will get the disease and a 50% chance that he will be a carrier. Works Cited Bjorklund, Ruth. Sickle Cell Anemia. Marshall Cavendish, 2010. Eldra Solomon, Linda Berg, Diana W. Martin. Biology. Cengage Learning, 2010. John David Rainer, Foundation of Thanatology. Genetic Disease: The Unwanted Inheritance.

Routledge, 1989.