Question

Enzyme ‘Taq polymerase’ used in PCR, has been isolated from bacteria
A) Agrobacterium tumefaciens
B) Thermus aquaticus
C) Streptomyces albus
D) Escherichia coli

Answer 1

Polymerase chain reaction is a technique used to create more copies of a fragment of DNA segment. This technique is used in molecular biology. The various steps of PCR include denaturation, elongation and annealing. Taq polymerase enzyme is used in the process of elongation.

Complete answer:
Polymerase chain reaction is a biological technique used in molecular biology for creating several copies of DNA fragments. The main principle behind this method is enzymatic replication of DNA. Using primer mediated enzymes, a short segment of DNA is amplified. The enzyme responsible for this process is DNA polymerase enzyme. So, the various components required for the process of PCR includes- DNA templates, DNA polymerase, oligonucleotide primers and deoxyribonucleotide triphosphates along with a buffer system.
-DNA template is the DNA sequence which needs to be amplified.
-The DNA polymerase enzyme used is Taq polymerase.
-Oligonucleotide primers are the short stretches of DNA which are complementary to the 3’ ends of sense and antisense strands.
-Deoxyribonucleotide triphosphate provides the energy.
-Buffer system- It is important for the stability and activity of polymerase enzymes.
Steps of PCR- It involves 3 major steps-
-Denaturation,
-Annealing
-Elongation.
Denaturation- The mixture is heated at a temperature of 94 degree celsius for about 1-2 minutes. The heating causes the hydrogen bonds to break between two strands of DNA.a nd forms a single stranded DNA. This acts as the template for amplification.
Annealing- The temperature in this step is reduced to 54-60 degree celsius for around 20-40 seconds. Primers which are the single stranded DNA sequences bind to their complementary sequence. As there are two separated strands running in opposite directions, two primers are formed- a forward primer and a reverse primer.
Elongation- The temperature is again raised to 72-80 degree celsius and the use of Taq polymerase enzyme is made. This enzyme causes elongation in 5’ to 3’ direction. The Taq polymerase enzyme is isolated from bacterium Thermus aquaticus. It can tolerate very high temperatures. This enzyme is attached to the primer and adds the DNA bases. At the end, a double stranded DNA molecule is formed. After repeating this process for several times, we can obtain a large number of DNA sequences in a short period of time.

Hence, the correct answer is option (B).

Note: PCR is used widely in the field of medicine, forensic science and for research and genetics. This method plays an important role in gene mapping. The enzyme Taq polymerase is obtained from bacteria Thermus aquaticus and is stable at very high temperatures.