a What is the melting temperature of the DNA sequence GGTCAT

a. What is the melting temperature of the DNA sequence GGTCATT?

b. How much energy is required for a helicase enzyme, which binds to the above double stranded DNA base sequence, to denature the duplex completely?

Solution

a.     What is the melting temperature of the DNA sequence GGTCATT?

GGTCATT

CCAGTAA

Tm (melting temperature) which indicates the temperature where the DNA molecule is 50 % degenerated (DNA is single stranded).

Melting temperature of the primer (approximation):

T_m = (2) (number of A+T pairs) + (4) (number of G+C pairs) or

T_m = (A + T)× 2C + (G+C) × 4C= (4) × 2C + 3× 4C= 20 C

b. How much energy is required for a helicase enzyme, which binds to the above double-stranded DNA base sequence, to denature the duplex completely?

Helicase will unwind the nucleic acid strands and they will use the energy derived from ATP hydrolysis. The standard state free energy of denaturation is approximately 2.5 and 5.0 kcal/mole for A-T and G-C base pairs.

Energy needed to unwind the DNA sequence GGTCATT is 2.5 kcal/mol x number of AT basepairs + 5 kcal/mol x number of GC basepairs

=2.5 kcal/mol x 4 + 5 kcal/mol x 3= 10 kcal/mol + 15 kcal/mol= 25 kcal/mol