Medical Laboratory Science Harr 8.1 Molecular Diagnostics: Molecular Methods

1. Which double-stranded DNA molecule has the highest melting temperature? A. An oligonucleotide with a repeating sequence of A-A-A at the 5´ end B. A molecule of 5,000 base pairs with a high number of A-T base pairs C. An oligonucleotide with a large number of repeating C-G-C codons D. A DNA polymer of 100,000 base pairs: C. An oligonucleotide with a large number of repeating C-G-C codons C The melting temperature of DNA refers to the temperature required to separate the molecule into single strands. The Tm is the temperature required to convert half of the DNA from dsDNA to ssDNA. This is done by breaking the hydrogen bonds between base pairs. A-T base pairs have two hydrogen bonds, while C-G base pairs have three. Therefore, molecules with a high proportion of C-G base pairs are more resistant to heat denaturation or melting.