18. Explain with reference to PCR. 
(a) A specific enzyme helps in amplification in PCR. Name the bacterium from which it is isolated and state how its 
thermostable nature is helpful, 
(b) Explain its use in molecular diagnosis. 

Kindly refer the link below for answer

The specific enzyme named Taq polymerase is obtained from the bacterium Thermus aquaticus. The PCR involves the denaturation of DNA by using high temperature. The Taq polymerase remains stable at this temperature and hence is used in amplification of DNA in PCR.

(b). The PCR is used in molecular diagnosis by detecting the low amount of DNA of infectious agents by amplifying their piece of DNA to form many copies. The amplified DNA can be then easily identified by using other testing procedures. So, it helps in early and highly sensitive detection of disease causing agents in body by amplifying their specific DNA.  

For example: 
PCR helps in detection of infectious agents by virtue of specific genes. It helps in early detection of  HIV (causing AIDS), even before the onset of disease.  The specific primers to the targeted sequences in the DNA of a virus are used to amplify the viral nucleic acid after it has been extracted from the blood. Then, the amplified viral DNA can be quantified and identified.


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