Medical Advancements

By Yi-Xuen Tan

1 - PCR Test 

Beyond testing for Covid-19, PCR tests can be used for other medical uses. They can be used to detect pathogens that can result in other diseases, or to identify small amounts of cancer cells and genetic changes that can cause disease. 

A polymerase chain reaction (PCR) test detects genetic material (DNA/RNA) from a pathogen or abnormal cell sample. PCR testing amplifies small parts of genetic material in a process called ‘molecular photocopying’; scientists can hence use this method, instead of having to use large amounts of DNA for genetic and molecular testing. 

The test involves:

• DNA primers 

• a short, single-stranded nucleic acid (biomolecules that are involved in the storage and expression of genomic information) used by all living organisms in the initiation of DNA synthesis. These are required to be bound to the template DNA before DNA polymerase can begin a complementary strand.

• DNA bases

• Enzymes

• Taq enzyme - a thermostable DNA polymerase, named after the thermophilic bacteria Thermus aquaticus it was extracted from. It stimulates the repetitive step of amplifying specific DNA sequences, working at temperatures higher than bodily enzymes can.

• Buffer solution

• Premixed solutions that contain necessary ingredients for carrying out the PCR test. These include concentrated DNA polymerase reaction buffers, loading buffers, and more. 

• Thermal cycling, to help replicate the genetic material sequences

  
  

  Process

For DNA:

DNA duplication - After collecting the sample, a researcher heats up the sample in a specialised machine; this separates the DNA into two pieces of single-stranded DNA. When the reaction cools, it allows primers to attach to the template DNA sequences. These are then heated up again, to allow an enzyme called Taq polymerase to add DNA bases to the templates. 

This process is replicated by the machine to create as many copies of the original DNA segment as needed. In a diagnostic PCR test, the machine can detect the presence of a pathogen after replicating the genetic material. 

For Viruses:

RNA undergoes a different process at first, called reverse transcriptase PCR (rtPCR). This is because viruses consist of RNA - not DNA. The process turns RNA into DNA before copying it.

Using onsite analyzers, the results of a PCR test are fast, but they may take longer due to processing delays in off-site labs.