DNA denaturation and renaturation processes are used for genetic research and studies. In the process of denaturation, an unwinding of DNA double-strand takes place, resulting in two separate single strands on applying high temperature, extreme pH, etc. Separate single strands rewind on cooling and the process is known as renaturation.
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Denaturation and renaturation kinetics are used to determine the size and complexity of the genome. It is also used to understand the relativity of two genomes and repetitive sequences present in a genome.
Difference between Denaturation and Renaturation of DNA
The table below shows the main difference between Denaturation and Renaturation of DNA
|
Denaturation of DNA |
Renaturation of DNA |
|
Double-stranded DNAs are converted to single strands |
Denatured single strands of DNA, which are complementary, form double strands |
|
Denaturation occurs on heating |
Renaturation occurs on cooling |
|
Unwinding of DNAs take place |
Rewinding of DNAs take place |
|
In this process, hydrogen bonds between complementary base pairs of two DNA strands are broken |
There is a formation of hydrogen bonds between complementary base pairs of two strands to form double strands |
|
The rate of UV absorbance (260nm) increases |
The rate of UV absorbance decreases |
|
Viscosity decreases |
Viscosity increases |
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:
- 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.
- 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.
- 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.
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