When a person has sickle cell anemia, the hemoglobin protein forms long chains that change the shape of the red blood cell. So, instead of a disc shaped structure that moves easily through blood vessels, sickled blood cells are shaped like bananas. The reason they have a sickled shape is because the underlying gene has the wrong instructions.
Explanation:
Recall that DNA contains four bases: Adenine, Guanine, Cytosine, and Thymine. The sequence of A's, T's, G's, and C's are what determines the protein that is built. Each set of three bases will code for a single amino acid. Proteins are simply chains of amino acids. To make proteins, DNA must send its code sequence to the ribosomes in the cell, but it needs a messenger to do that. Transcription is the process where DNA is converted to a molecule of messenger RNA (mRNA). The mRNA is then used to build a protein like hemoglobin. To determine the amino acid sequence of the gene, you must transcribe the DNA to RNA. The base pair rule is used to create RNA, but RNA does not contain thymine, it contains URACIL instead. This is why codon charts have U's in them and no T's.
A codon chart tells you what bases in RNA code for what amino acids. The ribosome combines all the amino acids to create a single protein, like hemoglobin. It takes three bases to determine one amino acid. Amino acids are usually abbreviated. GUC makes the amino acid valine, abbreviated as "Val". Sometimes, one of the letters in DNA gets switched with another letter, causing a mutation in the DNA. Many mutations don't have any effects, but some will change the amino acid made by the ribosomes. In the case of sickle cell anemia, just a single letter change alters the shape of the hemoglobin protein
Basically, the gene gets the wrong instructions, and ends up forming a sickle shaped blood cell.
