When Double-Stranded DNA Is Heated, the Two Strands Separate into Single

question 64

Essay

When double-stranded DNA is heated, the two strands separate into single strands in a process called melting or denaturation.The temperature at which half of the duplex DNA molecules are intact and half have melted is defined as the T_m.
A.Do you think T_m is a constant, or can it depend on other small molecules in the solution? Do you think high salt concentrations increase, decrease, or have no effect on T_m?
B.Under standard conditions, the expected melting temperature in degrees Celsius can be calculated from the equation T_m = 59.9 + [0.41 × %(G + C)] − (675/length of duplex).Does the T_m increase or decrease if there are more G + C (and thus fewer A + T) base pairs? Does the T_m increase or decrease as the length of DNA increases? Why?
C.Calculate the predicted T_m for a stretch of double helix that is 100 nucleotides long and contains 50% G + C content.

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