Question

When sufficient heat is applied, double-stranded DNA denatures into two single-stranded molecules as the heat breaks all of the hydrogen bonds. In an experiment, molecules of single-stranded DNA from species X are separately hybridized with supoosedly homologous single-stranded DNA molecules from five species (A-E). The hybridized DNAs are then heated, and the temperature at which complete denaturation occurs is recorded. Based on the data, which species is probably most closely related to species X

Answer 1

Answer and Explanation:

When sufficient heat is applied, DNA unwinds, and the hydrogen bonds that grip the strands together weaken and break. The process of breakdown of double-stranded DNA into single strands is called DNA denaturing. The temperature at which double-stranded DNA is half denatured is termed as Tm (melting temperature). By the absorbance of the DNA solution, the amount of strand melting is measured at 260nm. At this wavelength, nucleic acids absorb light. When DNA strands come together, the proximity of the bases in the DNA strands reduces some absorbance. When the DNA strands separate, the absorbance rises 30% to 40%, and quenching of the absorbance disappears. This is known as hyperchromicity. By using DNA denaturation, the sequence difference between the two DNA sequences can also be detected. When double-strand DNA is heated, it denatured into a single-stranded state. The mixture is cooled to allow the strands to re-hybridize. Hybrid molecules are formed among related sequences.