Biology · Biotechnology: Principles and Processes · NEET
Taq polymerase is a thermostable DNA polymerase enzyme taken from a heat-loving bacterium called Thermus aquaticus. In PCR, the DNA is heated to a very high temperature many times. A normal enzyme would break at that heat, but Taq stays active, so it can keep building new DNA strands cycle after cycle. Memory hook: "Taq" comes from Thermus aquaticus, and it lives in hot springs, so it does not mind the heat.
Taq polymerase from Thermus aquaticus stays active through the high-heat denaturation step and does the actual DNA building in the extension step of every PCR cycle.
Your doubts, answered
Why is a special Taq polymerase used in PCR instead of a normal DNA polymerase?
In PCR the tube is heated to about 94-95 degrees Celsius in every cycle to separate the two DNA strands (denaturation). A normal DNA polymerase is a protein and would break (denature) at this heat, so you would have to add fresh enzyme after every cycle. Taq polymerase is thermostable, meaning it stays active even at these high temperatures. So you add it once and it works through all 25-30 cycles.
What does the word 'thermostable' mean here?
Thermostable means 'stable at high temperature'. The enzyme does not lose its shape or activity when heated. Taq polymerase can survive the repeated high-temperature denaturation steps of PCR and still keep joining nucleotides to make new DNA. This is the single most important property NEET wants you to remember.
Where does Taq polymerase come from?
It is isolated from a bacterium named Thermus aquaticus. This bacterium naturally lives in hot springs, so its enzymes are already built to work at high temperature. NCERT states the thermostable DNA polymerase used in PCR is isolated from Thermus aquaticus. The name 'Taq' is made from the first letters: T-aq.
Is Taq polymerase the same as ordinary DNA polymerase?
Its job is the same: it adds nucleotides to a growing DNA strand using the template and a primer. The difference is only its heat tolerance. Ordinary DNA polymerase (like the ones inside human or E. coli cells) works near body temperature and breaks at high heat, while Taq keeps working at PCR temperatures.
In which step of PCR does Taq polymerase actually work?
Taq works in the extension (or elongation) step, which happens at about 72 degrees Celsius. After the primers anneal (bind) to the single strands, Taq extends the primers by adding nucleotides, building the new complementary strand. It does not do the denaturation or annealing steps itself.
⚠️ The NEET trap ✗ Taq polymerase is chosen because it works faster than other enzymes. ✓ Taq polymerase is chosen because it is thermostable and stays active during the high-temperature denaturation of each PCR cycle. 🧠 NEET options often swap 'thermostable / survives high temperature' with a distractor like 'fastest' or 'cuts DNA'. The examiner tests the reason (heat tolerance), not speed. Taq builds DNA, it does not cut it.
Real NEET questions
NEET 2016
The Taq polymerase enzyme is obtained from:
A · Thermus aquaticus ✓
B · Thiobacillus ferroxidans
C · Bacillus subtilis
D · Pseudomonas putida
Solution: Repeated PCR heating needs a thermostable DNA polymerase (Taq) that stays active through the high-temperature denaturation step. NCERT states it is isolated from Thermus aquaticus. The other bacteria are used elsewhere (bioleaching, superbug) and are not the source of Taq.
NEET 2023
Thermostable DNA polymerase used in PCR was isolated from:
A · Agrobacterium tumefaciens
B · Bacillus thuringiensis
C · Thermus aquaticus ✓
D · Escherichia coli
Solution: PCR uses repeated high-temperature denaturation, so the DNA polymerase must be thermostable. This thermostable polymerase (Taq) is isolated from Thermus aquaticus and stays active during the heat step. Agrobacterium gives the Ti plasmid, Bacillus thuringiensis gives Cry proteins, and E. coli is a common host, so none of these are the source.
NEET 2020
Match the organism with its use in biotechnology: (a) Bacillus (b) Thermus aquaticus (c) Agrobacterium tumefaciens (d) Salmonella typhimurium with (i) Cloning vector (ii) Construction of first rDNA (iii) DNA polymerase (iv) Cry proteins
A · (a)-iii; (b)-ii; (c)-iv; (d)-i
B · (a)-iii; (b)-iv; (c)-i; (d)-ii
C · (a)-ii; (b)-iv; (c)-iii; (d)-i
D · (a)-iv; (b)-iii; (c)-i; (d)-ii ✓
Solution: Thermus aquaticus gives the thermostable DNA polymerase (b-iii). Bacillus is linked with Cry proteins (a-iv), Agrobacterium tumefaciens gives a cloning vector via the Ti plasmid (c-i), and the first recombinant DNA used a plasmid of Salmonella typhimurium (d-ii). This gives option D.
Solved Biotechnology: Principles and Processes NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What is the full form or origin of the name 'Taq'?
'Taq' is not an abbreviation of a chemical. It comes from the name of the bacterium Thermus aquaticus, taking T from Thermus and aq from aquaticus.
Why does Taq polymerase not get destroyed at high temperature?
Because it evolved in Thermus aquaticus, a bacterium living in hot springs. Its protein structure is naturally stable at high temperatures, so it does not denature during the 94-95 degree Celsius denaturation step of PCR.
Does Taq polymerase cut DNA?
No. Taq is a polymerase, so it builds (synthesises) new DNA by adding nucleotides. Cutting DNA is done by restriction enzymes (endonucleases), not by Taq. Confusing these is a common NEET trap.
Is Taq polymerase used to join DNA fragments like DNA ligase?
No. DNA ligase joins two DNA fragments end to end. Taq polymerase extends a primer to make a full new strand along a template. They do different jobs.
At what temperature does Taq polymerase work best in PCR?
Its extension step in PCR is usually carried out around 72 degrees Celsius, where Taq adds nucleotides efficiently while still tolerating the earlier high-heat denaturation step.
