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Read the following lines and answer question on the basis of the same:

Testing for COVID-19 using PCR

The objective of COVID-19 testing is to identify part of the corona viral genome in the patient sample. As, there is insufficient viral RNA to detect directly in the patient sample, a process called reverse transcription polymerase chain reaction (RT-PCR) is used for amplification. Short single stranded pieces of DNA called primers recognize unique RNA sequences within the viral genome. When double-stranded DNA copy of the target region of the viral RNA is produced, it undergoes successive rounds of amplification during which the DNA undergoes denaturation. Two primers anneal to their target sequences and then Taq polymerase extends a new strand. The number of copies of the target region of the viral genome doubles with each cycle. In practice, the virus is typically detected in 35 cycles of PCR, after which the number of DNA copies produced will be 235. PCR based diagnosis is faster, safer and more specific because it does not use live pathogens.

(i) The sequence of steps in PCR is- 

(a) Denaturation, annealing, extension 

(b) Annealing, denaturation, extension 

(c) Extension, annealing, denaturation 

(d) Denaturation, extension, annealing

(ii) A primer is- 

(a) short ss piece of DNA 

(b) short ds piece of DNA 

(c) short ds piece of RNA 

(d) Either (b) or (c)

(iii) After n cycles, the number of DNA copies produced are- 

(a) n2

(b) 2n

(c) n x 2

(d) n ÷ 2

(iv) Taq DNA polymerase synthesizes DNA at a temperature of around 700 C as it is- 

(a) thermophilic 

(b) thermostable 

(c) thermoregulator 

(d) thermolabile

(v) Culture based approaches for detecting pathogens, as compared to PCR based assays area) are-

(a) Faster, safer but less specific 

(b) Slower but safer and more specific

(c) Slower, less safer and less specific 

(d) Slower, less safer but more specific.

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1 Answer

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(i) (a) Denaturation, annealing, extension

(ii) (a) short ss piece of DNA

(iii) (b) 2n

(iv) (a) thermostable

(v) (c) Slower, less safer and less specific

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