Sickle Cell Anemia - Essay Example

Each cell of a human body consists of a nucleus. All the genetic material required for the physical characteristics of a human being are present in the 23 chromosomes located inside the nucleus. A single unit of a DNA is called a gene. A gene provides us with the directions required for synthesizing a protein and these proteins are responsible for our traits. Each gene consists of a specific order of nucleotides and these nucleotides dictate the order of amino acids which in turn form chains and links to form proteins.

These sequences of amino acids are very important because they are responsible for the shape, structure and characteristics of a protein. Any change in this sequence is called a mutation and the effects could be dreadful. Change in this sequence could cause the characteristics of a protein to change completely. Mutation is basically the spontaneous change in the structure of a gene or chromosome. 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.

The synthesis of any protein is a two-step process. Firstly the instructions in the gene, present in the DNA, are copied onto a messenger RNA (mRNA) with the help of RNA polymerase. The synthesis of the mRNA is a complex process. This stage is known as transcription. In this stage, the RNA polymerase breaks the bonds of the double helical molecule of DNA and with the help of base pairing, different RNA nucleotides are added one at a time. To understand the concept of base pairing, one needs to understand the structure of RNA first.

Each RNA molecule consists of a nitrogenous base, sugar and a phosphate molecule. But unlike DNA, RNA is single stranded. During transcription, each DNA nucleotide is paired with a complimentary RNA nucleotide. The complimentary base pairs are as follows: Guanine with Cytosine Thymine(DNA) pairs with Adenine (RNA) Adenine (DNA) pairs with Uracil(RNA) One of the basic differences between DNA and RNA is of the nitrogenous bases. In place of Thymine, RNA contains Uracil. This method of base pairing ensures that the correct sequence of nucleotides, present in the DNA, is copied onto the mRNA chain. (Gary H. Perdew) These instructions consist of the sequence in which the amino acids should be linked together to form the protein.

In this case, the new mRNA formed at the 11th chromosome is encoded with the mutant code. Then the information on the mRNA bases is translated by the ribosomes so that they can place amino acids in the given order to form the protein that was coded for by the gene in this case, the beta s globin. Three nucleotides in an mRNA molecule are the code for one amino acid. This set of nucleotides is known as a codon. This sequence of codons is actually the code for the sequence of amino acids in a protein.

Because of the point mutation the HBB gene