The type mutation that leads to replacement of valine for glutamate in sickle cell disease is?
Ans. A. Point mutation. (Ref. Robbin's Pathology8th/pg. 873)Missense mutations and nonsense mutations are examples of point mutations, which can cause genetic diseases such as sickle-cell disease and thalassemia respectively.Point mutations result from the substitution of a single nucleotide base by a different base, resulting in the replacement of one amino acid by another in the protein product. The mutation giving rise to sickle cell anemia is an good example.Frameshift mutations may result in severe genetic diseases such as Tay-Sachs disease.# Point mutations. Point mutations result from the substitution of a single nucleotide base by a different base, resulting in the replacement of one amino acid by another in the protein product.a) missense mutations: The mutation giving rise to sickle cell anemia is an excellent example of a point mutation that alters the meaning of the genetic code.b) nonsense" mutations: In contrast, certain point mutations may change an amino acid codon to a chain termination codon, or stop codon. Such "nonsense" mutations interrupt translation, and the resultant truncated proteins are rapidly degraded.# Frameshift mutations: Frameshift mutations occur when the insertion or deletion of one or two base pairs alters the reading frame of the DNA strand.# Trinucleotide repeat mutations- characterized by amplification of a sequence of 3 nucleotides.- all affected sequences share the nucleotides guanine (G) and cytosine (C).- Another distinguishing feature of trinucleotide repeat mutations is that they are dynamic (i.e., the degree of amplification increases during gametogenesis).- For example, fragile X syndrome, prototypical of this category of disorders.Additional Educational points:In sickle cell hemoglobin (HbS), Val replaces the a6 Glu of HbA, creating a "sticky patch" that has a complement on deoxyHb (but not on oxyHb). De- oxyHbS polymerizes at low O2 concentrations, forming fibers that distort erythrocytes into sickle shapes.
Point mutation
Silent mutation
Nonsense mutation
None
Molecular Genetics