DNA is a chemical chain that exists in the form of a double helix.
Whenever there is a change in the structure or amount of DNA in an organism, it is called a mutation. There are several different types of mutations, depending on where the change occurs and how the DNA is affected. A nonsense mutation is a single base substitution or a point mutation. When a nonsense mutation occurs, only one base in the DNA strand is changed.
A missense mutation involves a single base in the DNA strand.
DNA is made up of a double helix of long strands of nucleotides that have nitrogenous bases attached to them. The four bases are adenine, thymine, guanine, and cytosine. Nucleotides join together to form long chains of polynucleotides. The two strands are held together by hydrogen bonds between complementary base pairs.
Each base is either a purine base or a pyrimidine base, depending on the number of chemical rings in its molecular structure. Purine bases have two chemical rings and include adenine and guanine. Pyrimidine bases have a single chemical ring and include cytosine and thymine. Purine bases always base pair with pyrimidine bases, or more specifically, adenine with thymine and cytosine with guanine.
A person whose cystic fibrosis transmembrane regulatory genes are mutated will have cystic fibrosis.
When proteins are synthesized in a cell, the information for each protein is carried in the genes along the DNA strands. A triplet of bases, or codon, in a gene codes for a specific amino acid, which is a building block for protein molecules. The sequence of amino acids that will be used to form a protein is determined by the sequence of codons. Any change in these codons, if not repaired, can affect the formation of the protein.
Cystic fibrosis is characterized by excess mucus in the lungs.
To form a protein, two processes take place. First, the DNA is transcribed into messenger RNA (mRNA) within the nucleus. mRNA is a single-stranded molecule, so it can exit the nucleus through small holes or pores in the nuclear membrane. The mRNA now carries the information to synthesize a protein during translation in the cytoplasm of the cell.
Nonsense mutations can cause genetic disorders in unborn babies.
Nonsense mutations affect the genetic coding region of DNA. When a nonsense mutation occurs, a base is changed so that its amino acid triplet code changes to code for a stop codon. Termination codons are TTA, TAG or TGA. A nonsense mutation causes the transcription of DNA to mRNA to stop, which means that the mRNA strand is shorter than it should be. The earlier this mutation occurs in the gene, the shorter the mRNA and the more truncated the protein, making it less likely to work.
There are several genetic diseases caused by nonsense mutations. Cystic fibrosis is caused by mutations in the gene that encodes the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Some patients have a nonsense mutation in the gene, which causes much of the protein to not form. Any defect in this protein causes the different symptoms of the disease. Other conditions that can be caused by nonsense mutations include Duchenne muscular dystrophy, beta thalassemia, and Hurler syndrome.