RT PCR | IAS GYAN

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Context

India reported 18,819 new Covid-19 cases and 39 deaths in the last 24 hours. With rising Covid-19 cases in India, states have been asked to screen 2% of the international passengers coming to India at random and send all positive samples for genome sequencing.

RT-PCR

The real-time polymerase chain reaction (RT-PCR) test is the most commonly used one for Covid-19. It is primarily based on PCR, a process that repeatedly copies and amplifies the specific genetic fragments of the virus, ensuring that there is enough of a sample to conduct the analysis.
The RT-PCR test starts with a simple swab taken from inside a person’s throat or nose. Coronaviruses have RNA or ribonucleic acid as their genetic material. However, swabs from patients yield only a tiny quantity of RNA, which is not adequate for the testing process.
To overcome this problem, the RNA — a single-strand molecule — is converted into a two-strand DNA using an enzyme. This is known as reverse transcription.
Researchers select specific areas in the genome that do not mutate rapidly as the virus evolves, and create copies of these using the PCR process.
The next step is the use of primers. These are small pieces of DNA designed only to bind to the selected DNA sequence of the SARS-CoV-2’s viral genome. Along with primers, the process uses a fluorescent dye, which acts as the probe.
The patient sample, primer and probe are together left in the PCR machine for the binding process to take place. A fluorescent signal marks the presence of the virus.
The time duration for the testing process is around four to eight hours.