DNA denaturation, reannealing, hybridization are processes based on the chemistry of base pairing between complementary strands of DNA double helix.
The two strands of DNA double helix stay together via base pairing of nitrogenous bases: adenine, thymine, guanine, and cytosine. Remember, adenine (A) makes two hydrogen bonds with thymine (T), while guanine (G) forms three hydrogen bonds with cytosine (C). When these hydrogen bonds break, the double helix melts and generates two single strands. This process is called DNA denaturation (or DNA melting). High temperatures and certain chemicals induce denaturation of DNA. Because there are more hydrogen bonds between G and C base pairs than A and T base pairs, the more G-C base pairs a strand of DNA has, the higher the melting temperature.
Luckily, DNA denaturation is a reversible process. When the temperature is cooled down slowly, complementary single strands come together and make appropriate hydrogen bonds. As a result of this reannealing process, the two single strands recombine to form the double helix.
However, in a single-stranded state, DNA could bind to another single-stranded DNA of different origin if they have sufficient complementarity or enough base pairing. This is referred to as nucleic acid hybridization.
Practice Questions
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Key Points
• DNA denaturation is unwinding of the double helix at higher temperatures or extreme chemical conditions.
• When these conditions return back to favorable, DNA double helix forms again in a process of reannealing.
• DNA strands are not in all-out loyalty to each other: they can make hybridization, which is forming double strands with other complementary strands.
Key Terms
DNA denaturation: Refers to the melting of double-stranded DNA to generate two single strands.
Nitrogenous bases: Organic molecules, which are part of the nucleotides in DNA, showing base-like chemical properties.
Base pairing: The specific way in which bases of DNA line up and bond to one another; A always with T and G always with C.
Double helix: The structure of DNA which looks like a twisted staircase.
Hybridization: The spontaneous pairing of complementary DNA sequence by hydrogen bonding to create a double-stranded molecule.
