1. Chapter 49 – THE HELIX-TO-COIL TRANSITION IN DNA 49:5. A HELIX-TO-COIL TRANSITION MODEL 49:6. APPLICATION OF THE MODEL TO UV ABSORPTION DATA

2. 49:5. A HELIX-TO-COIL TRANSITION MODEL helical sequence coil sequence N H helical unit Partition for melting of 1 helical unit: Partition for melting of 1 helical sequence: Partition function:

3. 49:5. A HELIX-TO-COIL TRANSITION MODEL Diagonalize matrix: Partition function becomes: Eigenvalues: Fraction of units in the helical state: Relative number of helical sequences: Average number of helical units per helical sequence: H melting temperature:

4. 49:6. APPLICATION OF THE MODEL TO UV ABSORPTION DATA Estimate: Enthalpy of melting: Fit of UV data yields: There are 29 sequences per 1000 base units

5. COMMENTS -- Investigated salmon DNA in d-ethylene glycol. -- UV absorption spectroscopy monitors amine-base stacking in the DNA helical phase. -- It can detect for helix-to-melt transition. -- A simple model describes this melting transition.