Fatal mutation

The deletion of a single base from a DNA molecule can be a fatal mutation. Substitution of one base for another is often not as serious a mutation. Why ... 

Describe the structural differences between DNA and RNA. The monomers in nucleic acids are called nucleotides. What are the three parts of a nucleotide The compounds adenine, guanine, cytosine, and thymine are called the nucleic acid bases. What structural features in these compounds make them bases DNA exhibits a double-helical structure. Explain. Describe how the complementary base pairing between the two individual strands of DNA forms the overall double-helical structure. Flow is complementary base pairing involved in the replication of the DNA molecule during cell division Describe how protein synthesis occurs. What is a codon, and what is a gene The deletion of a single base from a DNA molecule can constitute a fatal mutation, whereas substitution of one base for another is often not as serious a mutation. Explain. 

Ans. Radiotherapy and chemotherapy use radiation and chemicals, respectively, to cause fatal mutations in the DNA of cancer cells. Cancer cells are damaged more by radiotherapy and chemotherapy than are normal cells because cancer cells grow more rapidly. Improved radiotherapy causes minimal damage to healthy tissues by delivering the minimum effective radiation dose. The radiation is confined as much as possible to the cancerous tissues by using collimated (narrowed and focused) radiation beams. Chemotherapy is similarly improved by choosing chemicals that attack cancer cells more selectively than healthy cells. 

Fatal hereditary disorder that typically presents in the neonatal period. Clinical features include an array of hepatic, renal and neurological dysfunctions. Patients with Zellweger syndrome rarely survive the first year of life. The disease is caused by mutations in the Pex proteins leading to an defective import of peroxisomal matrix proteins and consequently to a loss of most peroxisomal metabolic pathways. 

Type I Crigler-Najjar syndrome is a rare autosomal recessive disorder. It is characterized by severe congenital jaundice (serum bilirubin usually exceeds 20 mg/dL) due to mutations in the gene encoding bilirubin-UGT activity in hepatic tissues. The disease is often fatal within the first 15 months of life. Children with this condition have been treated with phototherapy, resulting in some reduction in plasma bilirubin levels. Phenobarbital has no effect on the formation of bilirubin glucuronides in patients with type I Crigler-Najjar syndrome. A liver transplant may be curative. 

Purine nucleoside phosphorylase (PNP) deficiency engenders a combined immunodeficiency and neurologic abnormalities and is usually fatal in childhood (G4). Patients with PNP deficiency have profound lymphopenia and a small thymus with poorly formed Hassall corpuscles. Lymphocyte enumeration shows markedly decreased numbers of T cells and T-cell subsets, with normal percentages of B cells. Point mutations and a splicing mutation have been identified in some PNP-deficient patients (H4). 

Defects of complex III. Like defects of complex I, these can be due to nDNA mutations or to mtDNA mutations. The only nuclear defect described thus far does not affect a complex III subunit, but an ancillary protein needed for proper assembly, BCS1L. Mutations in BCS1L can cause a Leigh s-syndrome-like disorder or a fatal infantile disease called GRACILE (growth retardation, aminoaciduria, cholestasis, iron overload, lactacidosis, and early death). 

Mutations in one nuclear gene (ATP12), encoding an ATPase assembly protein, have been associated with complex V deficiency in an infant with congenital lactic acidosis and a rapidly fatal disorder affecting brain, liver, heart, and muscle [19]. 

Avian influenza is extremely deadly, with a 60% fatality rate for infected human cases to date. The virus may become even more deadly through the process of reassortment and gradual adaptive mutation. 

Mutations in the protein that transports carnitine into cells decrease its rate of transport resulting in an intracellular deficiency of both carnitine and acetylcarnitine. The disease is characterised by progressive cardiac myopathy. It usually presents within the first five years of life and is fatal. 

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