Harr MLS Review Molecular Diagnostics questions with correct answers

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 - Answer 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. Which base pair sequence is most likely to serve as a binding site for a restriction endonuclease? A. A-T-T-C-A ; T-A-A-G-T B. C-T-A-C-T-G ; G-A-T-G-A-C C. C-A-C ; G-T-G D. A-A-G-C-T-T ; T-T-C-G-A-A - Answer D. Restriction endonucleases are enzymes that cut double-stranded DNA into fragments and are important tools used in molecular diagnostics. Each restriction enzyme recognizes a specific oligonucleotide sequence, and the size and number of fragments it produces when DNA is digested depend upon the number of times that sequence is repeated in the DNA molecule. Restriction endonucleases recognize palindromic sequences (i.e., the base sequence of complementary strands reads the same from opposite directions). The sequence A-A-G-C-T-T T-T-C-G-A-A