Question

Under standard conditions, the expected melting temperature in degrees Celsius can be calculated from the equation Tm = 59.9 + [0.41 × %(G + C)] - (675/length of duplex). Does the Tm increase or decrease if there are more G + C (and thus fewer A + T) base pairs? Does the Tm increase or decrease as the length of DNA increases? Why?

Answer 1

The melting temperature (Tm) increases with more G + C base pairs and decreases as the length of DNA increases.

Step-by-step explanation:

The melting temperature (Tm) is expected to increase if there are more G + C (and thus fewer A + T) base pairs. This is because G and C base pairs have three hydrogen bonds, while A and T base pairs have two hydrogen bonds. Therefore, a DNA sequence with more G + C base pairs will have stronger bondings and require a higher temperature to break the hydrogen bonds.

On the other hand, the Tm is expected to decrease as the length of DNA increases. Longer DNA sequences have a higher probability of having more weak points in the structure, such as regions with lower G + C content or repeated sequences. These weak points make the DNA structure less stable and easier to melt, resulting in a lower melting temperature.