Topic: Recombinant Dna And Biotechnology

Hybridization is the double-strand formation (or annealing) between two different single strands of DNA or RNA due to base-pairing of complementary regions. This phenomenon forms the basis of several DNA techniques.  

The principle that keeps two strands of DNA double helix together is base pairing (i.e. hydrogen bonding between specific nitrogenous bases). Adenine (A) makes two hydrogen bonds with thymine (T), while guanine (G) three hydrogen bonds with cytosine (C). Therefore, DNA strands when separated from each other can form a double helix with DNA or RNA strand of different origin if they have sufficient complementarity. Through this process, called hybridization, DNA-DNA or DNA-RNA hybrids form. This makes many techniques used in biology possible.

For example, one may use it to compare the genetic closeness of different organisms. Here, DNAs from two species are first mixed in a single solution, then denatured by temperature, and lastly reannealed to form hybrid DNAs, which become to have one strand from each species. As a next step, the temperature needed to melt or denature hybrid DNAs is determined. Higher the temperature required for denaturation, it means there is much more complementarity between hybridized DNA strands. More complementarity indicates more genetic closeness.

Another technique that stands on hybridization is in situ hybridization. This technique allows detecting certain genomic region or mRNA in an intact cell or even organism. To achieve that, researchers first design a DNA molecule or “probe” complementary to the target genomic region or mRNA. Then they send many of this probe molecule into cells to hybridize with target DNA or RNA.  Nowadays, probe molecules mostly bear a fluorescent label on them. The name of the technique, in that case, becomes FISH (fluorescent in situ hybridization). With fluorescent labelling of a probe to target mRNA, it is possible to detect in which part of the organism the gene of interest is expressed. 

Practice Questions

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Key Points

• Hybridization refers to the formation of a double-stranded molecule by two single-stranded DNA or RNA molecules due to base-pairing of complementary regions. 

• This phenomenon helped scientists to design experiments, such as in situ hybridization, that interrogate the molecular aspects of genetics.  

Key Terms

mRNA: an RNA molecule that is complementary to one strand of DNA and a product of the transcription process.

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.

nitrogenous bases: organic molecules, which are part of the nucleotides in DNA, showing base-like chemical properties.

hybridization: the double-strand formation (or annealing) between two different single strands of DNA or RNA due to base-pairing of complementary regions

denature: a process in which proteins or nucleic acids lose their structure

FISH: fluorescence in situ hybridization that uses fluorescent probes that bind to only those parts of a nucleic acid sequence with a high degree of sequence complementarity

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