Question

If the initial number of template DNA molecules in a PCR reaction is 1000. What would be the number of product DNA molecules at the end of the 20 cycles closest to? 

A. 10

B. 101010101010

C. 101010101010101010

D. 101010101010101010101010

Answer 1

Hint: Polymerase chain reaction (PCR) is a technique used in laboratories widely in order to rapidly recreate billions of copies of any specific sequence of a DNA sample, thus allowing scientists to take a very small sample of DNA and amplify it to such a large extent, that facilitates in research and study of the sequence in a detailed way.

Complete answer: 

PCR is an enzymatic process during which a selected region of DNA is replicated repeatedly time and again to yield multiple copies of a specific sequence. This method combines the principles of complementary macromolecule hybridization along with those of macromolecule replication through a chain of numerous cycles. 

Each DNA multiplies in exponents of two. 

The number of the cDNA produced at the end of the say, n number of cycles of PCR would be equal to $2^n$. 

For 20 cycles, $ 2^20 = 1048576$.

Hence for 1000 copies in 20 cycles would yield, $ 1000 \times 1048576 = 1,04,85,76,000$.

This means that for 1000 DNA templates, we’ll obtain 101010101010 copies of the sample chosen, by the end of 20 cycles.

So, the correct answer is option (B), 101010101010.

Note: As, this technique can create multiple copies of a DNA sample, therefore using suitable primers, really small amounts of the specified pathogen (including bacteria and virus cells) can be easily detected in affected tissues, thus, making PCR an extremely useful technology in the diagnosis of diseases.