Difference Between Denaturation and Renaturation of DNA

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Introduction

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,  leading to two separate single strands on applying heat. Separate single strands rewind on cooling and the process is known as renaturation. 


Denaturation and renaturation kinetics are used to determine the size and complexity of the genome. It also helps to understand the relativity of two genomes and repetitive sequences present during a genome. 


Denaturation and Renaturation of DNA - Difference

The table below shows the foremost 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

Hydrogen bonds are formed 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. The stability of the DNA structure gets affected by many factors. 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 of DNA can be done by heating the DNA solution to approximately 90℃ or above. The temperature at which half of the DNA is denatured is named critical temperature or melting temperature, Tm. Tm depends on the length and composition of the DNA bases and other factors like 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 260 nm wavelengths. The rate of absorption is directly proportional to the rate of denaturation. The process of increased absorbance of denatured DNA is known as the hyperchromic effect. It occurs due to the unstacking of base pairs in the DNA.

  • Viscosity decreases, which reflects the physical change occurring in the DNA structure.


What is Renaturation?

Renaturation or the rejoining of complementary DNA strands is also known as annealing. When the temperature and pH return to optimum biological level, the unwound strand of DNA rewinds and the two DNA strands together form dsDNA.


If the DNA isn't 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 happens that forms 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. By the process of renaturation, absorption of UV (260nm) decreases and viscosity increases again.

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FAQs (Frequently Asked Questions)

1. Give a Brief Introduction on Denaturation and Renaturation

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,  leading to two separate single strands on applying heat. Separate single strands rewind on cooling and the process is known as renaturation. 


Denaturation and renaturation kinetics are used to determine the size and complexity of the genome. It also wants to understand the relativity of two genomes and repetitive sequences present during a genome.

2. When Does Renaturation Occur?

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. By the process of renaturation, absorption of UV (260nm) decreases and viscosity increases again.

3. What are the Types of DNA?

There are mainly three different DNA types:

  • A-DNA: It is a right-handed double helix similar to the B-DNA form. Dehydrated DNA takes an A form that protects the DNA during extreme condition such as desiccation. Protein binding also removes the solvent from DNA and the DNA takes an A form.

  • B-DNA: This is the most common DNA conformation and is a right-handed helix. Majority of DNA has a B type conformation under normal physiological conditions.

  • Z-DNA: Z-DNA is a left-handed DNA where the double helix winds to the left in a zig-zag pattern. It was discovered by Andres Wang and Alexander Rich. It is found ahead of the start site of a gene and hence is believed to play some role in the gene regulation.

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