What is Denaturation?
DNA has a double-stranded helical structure. There are various factors that affect the
stability of the DNA structure.
In the denaturation process, the hydrogen bonds between two strands are broken giving
rise to two single strands. The covalent bonds of DNA remain unaffected.
Denaturation can be brought by various methods:
1. Thermal denaturation: Denaturation can be done by heating (>80-90℃). The
temperature at which DNA is half denatured is called critical temperature or
melting temperature, Tm. Tm is dependent on the length and composition of the
DNA bases and other factors such as pH and denaturing agents.
2. Extreme pH: At high pH (>11.3), hydrogen bonds between base pairs of two
strands of DNA dissociate due to presence of abundant OH– ion. It results in
denaturation of DNA.
3. Other denaturing Agents: Low salt concentrations destabilise hydrogen bonds.
Formaldehyde and urea have a tendency to form hydrogen bonds with nitrogen
bases and aldehydes also prevent hydrogen bonding between base pairs by
modifying electronegative centres of nitrogenous bases.
Effect of denaturation of DNA:
• Increased absorption of UV light at 260nm wavelengths. The rate of absorption is
directly proportional to the rate of denaturation
• Viscosity decreases, which reflects the physical change occurred in the DNA
structure
What is Renaturation?
Renaturation is also known as annealing. When the temperature and pH return to
optimum biological level, the unwound strand of DNA rewind and give back the dsDNA.
If the DNA is not completely denatured, the renaturation process is fast and a one-step
process, but if the DNAs are completely denatured then the renaturation process
occurs in a two-step process. First complementary strands come together by random
collision and then rewinding takes place forming a double helix.
Renaturation occurs when the denatured DNAs are cooled in suitable conditions.
Renaturation also depends on temperature, pH, length and constituents of the DNA
structure. The renaturation rate is directly proportional to the number of complementary
sequences present.
With renaturation, absorption of UV (260nm) decreases and viscosity increases again.
