Skip to main content

What is PCR, learn about the detection process of Covid 19

detection of corona virus
RT-PCR: the test which detects Covid-19!

Welcome to fosterbrain.com dear visitors, you all might be aware of the test which detects the presence of Corona virus. Covid-19 is detected by a test called Real time PCR. Reading this article will make you understand what is PCR and also you will be able to learn about the detection  process of Covid 19.

Now, you must be wondering what's the full form of RT-PCR?

It's called Real time Reverse Transcription Polymerase Chain Reaction. 

To know it in details firstly you must understand what is a Polymerase Chain Reaction. PCR was invented by Kary Mullis in 1984. It is a method by which we can make millions to billions copies of our DNA sample. 

Now what is DNA? It stands for Deoxyribo Nucleic Acid. It is our genetic material. It holds all the instructions for our growth and development.

Like a guide book DNA contains all the information for making all the proteins required for our bodies. It is a double helical structure which means it has two strands arranged in a helix.

Helix means a twisted spiral shape. Its structure resembles a twisted ladder. It is made up of building blocks called nucleotides. 

Nucleotides are made of three parts:

A phosphate group, a five carbon sugar group called deoxyribose because it lacks an oxygen group on one of its carbons and lastly one of the four types of nitrogen bases.

Nitrogen base is an organic molecule with a nitrogen atom which has the properties of a base.

There are mainly 4 nitrogenous bases:
  • Adenine (A)
  • Cytosine (C)
  • Guanine (G) and
  • Thymine (T)
The sequence of these bases form the instructions. Each strand of DNA is composed of long sequences of these four bases, A, C, G and T linked into chains with alternating phosphate and sugar groups.

The bases always pair in the same way, A pairs with T, C with G. They are joined together by hydrogen bonds. The bases on one strand of the DNA pairs with the complementary bases on the opposite strand of DNA.

Each strand of DNA has a beginning called 5’ and an end called 3’. The two strands run in the opposite direction to each other which means one runs from 5’ to 3’ and the other runs from 3’ to 5’.

So they are also called antiparallel. This structure of DNA was discovered by Francis Crick and James Watson.

For almost all of the living beings DNA is their hereditary material.

But there exists some viruses which are called retroviruses whose genetic material is RNA. It stands for Ribo Nucleic Acid.

RNA is single stranded unlike the DNA and it consists of nitrogenous bases which are almost same as DNA, they are Adenine, Guanine, Cytosine but in place of Thymine it contains Uracil.

And the sugar group in the RNA is a ribose sugar which means it doesn't lack an oxygen group which lacks in DNA. 

Now let's come to our main topic i.e PCR

How is PCR done?

The machine in which PCR is performed is simply called a Thermocycler.

The DNA mixture are poured in test tubes and are put into the machine, it changes the temperature of the mixture so that it suits each step of the process.

What are the components of the DNA mixture?

It contains
  • the DNA segment: the target DNA sequence which we want to make copies
  • specific primers: short single stranded DNA sequences
  • heat resistant enzyme: mostly an enzyme called Taq Polymerase
  • the four different types of DNA nucleotides: A,T,G,C
  • the salts needed for the enzyme to act.
Now, the steps of PCR

So, PCR generally involves 3 steps
  • Denaturation
  • Annealing
  • Extension
Denaturation- In this step, the two stands of the DNA double helix are separated.

This happens by raising the mixture's temperature, which causes the hydrogen bonds between the complementary DNA to break. The temperature in this step is 94–98 °C .

Annealing- The temperature of the solution is lowered in this step due to which the primers bind to the DNA. One primer binds with each strand. Here the temperature is 50–65 °C. 

Extension- Using the original DNA strands as templates, new strands are made. An enzyme called DNA Polymerase joins the free DNA nucleotides together.

The order in which the nucleotides are added is determined by the sequence of nucleotides in the original DNA strand. The temperature is maintained at 75–80 °C in this step. 

After these steps, one cycle of PCR is completed resulting in two double stranded sequences of the DNA, each containing one new strand and one original strand.

The cycle when repeated many times can  produce million copies of DNA. It takes 2–3 hours to get almost billion copies of DNA.

That was all about the general process of PCR. PCR technology is developing day by day. Various types of PCR are developed till date. Real time PCR is one such type.

RT-PCR is a technique where an enzyme called Reverse Transciptase (RT) is used to generate complementary DNA from an RNA template.

This process of generating complementary DNA is called reverse transcription. RT-PCR is generally used to measure the amount of a specific RNA which is done by monitoring the reaction using florescent dyes.

The use of florescent dyes allows us to see the results immediately during the process so it is called real time RT-PCR. 

So now, before discussing about the process of the RT-PCR test for Covid-19, let us know something about the virus which causes the disease.

Which virus is responsible for Covid-19?

The virus strain which causes the Coronavirus disease 2019  is the Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

It is a single stranded RNA virus which means its genetic material is RNA and hence it is a retrovirus.

This virus spreads among people through close contact and through respiratory droplets produced when an infected person sneezes or coughs.

This virus binds with the respiratory cells and uses them to produce more viruses.

How RT-PCR test is done to detect Covid-19?

A sample is collected from the suspected person’s nose or throat using a swab. Swab means a small piece of soft material used for taking a small amount of substance from a body.

The sample is then treated with several chemicals that extract only the RNA present in the sample and removes other substances such as proteins and fats.

This extracted RNA is a mix of the person’s own genetic material and the virus’s RNA, if present.
 
The RNA is then reverse transcribed to DNA. Then they add additional short segments of DNA that are complementary to specific parts of the transcribed viral DNA.

If the virus is present then these segments attach themselves to target viral DNA.

The mixture is then placed in an RT–PCR machine that creates new, identical copies of the target sections of viral DNA.

The cycle is repeated again and again to copy the target sections of viral DNA. After each cycle the number doubles: two copies become four, four copies become eight, and so on. 

A standard real time RT–PCR set-up generally performs 35 cycles, which means at the end around 35 billion new copies are created of the sections of viral DNA from each strand of the virus in the sample.

As the new copies of the viral DNA are made, the marker attaches to the DNA strands and then releases a fluorescent dye, which is measured by the computer and is presented on the screen in real time.

After each cycle it tracks the amount of fluorescence in the sample. When a certain level of fluorescence is crossed then it confirms that the virus is present. 

It is also measured that how many cycles it takes to reach this level so that the severity of the infection can be estimated, less number of cycles means that the infection is more severe. 

So that was all about the RT-PCR test used to detect Covid-19, I have tried to explain it in a very simple way. Hope you all will like it.

If you want me to explain anything more let me know in the comment section.

You can subscribe this web site by email to receive all of our future articles. The subscribe button is available at the right top of this page. 



Comments

  1. Explain about the corona virus

    ReplyDelete
  2. This is really a nice and informative, containing all information and also has a great impact on the new technology. Check it out here: health life cares

    ReplyDelete
  3. Thanks for a very interesting blog. What else may I get that kind of info written in such a perfect approach? I’ve a undertaking that I am simply now operating on, and I have been at the look out for such info. coronavirus test

    ReplyDelete
  4. I invite you to the page where you can read with interesting information on similar topics. traitement punaises de lit 93

    ReplyDelete
  5. A round of applause for your blog article. Really thank you! Want more. same day pcr covid test houston

    ReplyDelete

Post a Comment

Popular posts from this blog

Tinsukia Zilla Parishad celebrates 73rd Republic Day

Sri Rajendra Nath Koiry, Chairman, Tinsukia Zilla Parishad today ceremoniusly hoisted the National Flag and unfurled the tricolor at the office premises of Tinsukia Zilla Parishad at sharp 07:30 IST. In his short speech Sri Koiry has briefly mentioned the significance of the 73rd Republic Day and the greatness of the Constitution of India a great Nation which is excelling in every sector of development under the leadership of a statesman like Narendra Modiji the honourable Prime Minister of India. The Chairman also commemorated the contribution of all the freedom fighters who martyred for Independence of India. Following are some of the glimpses of today's event. Thanks for visiting fosterbrain.com

What to do if you have diabetes in pregnancy

Diabetes during pregnancy is quite common a problem which needs serious attention and proper health care for the mother. Women go through several bodily changes during pregnancy and many a time their blood sugar level increases. This health condition is known as Gestational Diabetes in medical terminology. Though this disease fades away completely after delivery of the baby, it may cause some serious complexity in pregnancy.  Diabetes in pregnancy can create several negative impacts on the unborn baby. High level of blood sugar will also affect the mother's normal health. Diet becomes extremely important in case of high level of blood sugar in pregnancy. There is also high risk of immature baby and abortion for the increased level of blood sugar.  Amongst several bodily changes, blood sugar level of women also changes in pregnancy. In some pregnant women the blood sugar level increases beyond the recommended level. Women who have gained too much weight are at high risk

China patents it's first corona vaccine, will be available in markets by end of the year

The entire world is becoming restless for a working vaccine to combat with the novel corona virus pandemic. There is seemingly an unprecedented race amongst several countries to develop the corona vaccine. Russia, United States, Britain and China are leading the race ahead of other countries. Amidst the undeclared competition, China's first corona vaccine has been approved after that of Russia.  As per report of People's Daily, the largest newspaper group of China, vaccine Ad5-nCoV has been received patent rights. The vaccine has been developed in association with CanSino Biologics Inc. National Intellectual Property Administration of China has said that the patent for Ad5-nCoV has been approved on 11 August. This Chinese vaccine is currently undergoing stage-III trial in several countries and is expected a market launch by the end of this year.  Saudi Arab has said they are planning to start stage-III trial of the Chinese Vaccine in their country. CanSino Biologics