PCR technique and DNA denaturation
Which of the following statements about PCR is incorrect?
a. The DNA template is denatured using helicase.
b. PCR is used to obtain millions of copies of a specific region of DNA.
c. A thermostable DNA polymerase is used because of the high temperatures required in PCR.
d. Primers are needed because DNA polymerase cannot initiate synthesis, but can only elongate from an existing 3’OH.
Correct Answer: ✅ (a) The DNA template is denatured using helicase.
Explanation
The Polymerase Chain Reaction (PCR) is a widely used molecular biology technique that allows the amplification of a specific DNA sequence through a series of controlled temperature changes. The key steps involved in PCR include:
🔬 1. Denaturation
- In PCR, the DNA double strands are separated (denatured) by heating to 94–98°C.
- No helicase enzyme is involved — the high temperature alone is sufficient to break the hydrogen bonds between the complementary DNA strands.
🧬 2. Annealing
- Primers (short DNA sequences) bind to the complementary sequences on the single-stranded DNA.
- Annealing typically occurs at 50–65°C depending on primer length and GC content.
🏆 3. Extension
- A thermostable DNA polymerase (e.g., Taq polymerase from Thermus aquaticus) synthesizes a new strand by adding nucleotides to the 3’ end of the primer at 72°C.
✅ 2. Why the Other Statements Are True
| Statement | Explanation | True/False |
|---|---|---|
| (a) The DNA template is denatured using helicase. | PCR denatures DNA through high heat, not helicase. | ❌ False |
| (b) PCR is used to obtain millions of copies of a specific region of DNA. | PCR amplifies the target DNA exponentially over multiple cycles. | ✅ True |
| (c) A thermostable DNA polymerase is used because of the high temperatures required in PCR. | Taq polymerase can withstand high temperatures without denaturation. | ✅ True |
| (d) Primers are needed because DNA polymerase cannot initiate synthesis, but can only elongate from an existing 3’OH. | DNA polymerase requires a primer with a free 3’-OH group to initiate replication. | ✅ True |
🔥 3. Why Helicase is NOT Used in PCR
- In living cells, helicase unwinds DNA during replication by breaking hydrogen bonds between base pairs.
- In PCR, high heat (94–98°C) replaces the need for helicase by breaking the hydrogen bonds and separating the DNA strands.
- Helicase would not survive at such high temperatures because it is not heat-stable like Taq polymerase.
🧪 4. Key Components of PCR
| Component | Function |
|---|---|
| DNA Template | Contains the target sequence to be amplified. |
| Primers | Short DNA fragments that bind to complementary sequences on the template. |
| Taq Polymerase | Thermostable enzyme that synthesizes new DNA strands. |
| dNTPs | Nucleotides (A, T, G, C) for building the new DNA strand. |
| Buffer | Maintains the optimal pH and ion concentration for polymerase activity. |
5. Steps of PCR
Step 1: Denaturation
- Temperature: 94–98°C
- Breaks hydrogen bonds → Separates DNA strands
Step 2: Annealing
- Temperature: 50–65°C
- Primers bind to complementary DNA sequences
Step 3: Extension
- Temperature: 72°C
- Taq polymerase synthesizes new DNA strand
🌡️ 6. Why Taq Polymerase is Used
✅ Taq polymerase is isolated from the thermophilic bacterium Thermus aquaticus → Stable at high temperatures.
✅ It withstands repeated cycles of heating and cooling without denaturation.
7. Applications of PCR
1. Medical Diagnostics
- Detecting pathogens (e.g., COVID-19, HIV)
- Genetic disorder screening
2. Forensic Science
- DNA fingerprinting
- Crime scene analysis
3. Evolutionary Biology
- Studying genetic variation
- Analyzing ancient DNA samples
4. Research and Biotechnology
- Cloning and gene editing
- Mutation analysis
Summary
- PCR is a powerful technique for amplifying DNA.
- DNA is denatured by heat, not helicase.
- Taq polymerase is used for its thermostability.
- ✅ Correct Answer: (a) The DNA template is denatured using helicase.
79 Comments
Akshay mahawar
March 17, 2025Done 👍
Mahima Sharma
August 24, 2025Dna template denatured using template
Devika
August 26, 2025A
Ujjwal
March 17, 2025Done sir
Suman bhakar
March 17, 2025👍
Parul
March 22, 2025Easily done sir.
Abhilasha
March 25, 2025Done sir
Roopal Sharma
August 24, 2025Helicase is didn’t use in pcr beacuase it is use for unwinding the dna strand but high temperature is given in pcr and it can’t survive in hig temperature just like thermus aquaticus.
Soniya Shekhawat
August 24, 2025In PCR for denaturation using that high temperature not a helicase.
Mohd juber Ali
August 24, 2025High temperature sufficient for break hydrogen bond between complimentary dna
Khushi Pareek
August 24, 2025High temperature is given to denatured the template dna
Sakshi yadav
August 24, 2025In pcr the helicase are not used for denaturation the high temp. are required.the helicase enzyme are used for unwinding of strands
Arushi Saini
August 24, 2025Template is denatured through tempered
Mansukh Kapoor
August 24, 2025The correct answer is option 1st
DNA template is denatured using helicase statment is wrong because the DNA is denatured by giving 90°C to 95°C temp
Avni
August 24, 2025Correct Answer is (a) The DNA template is denatured using helicase.
Neha Yadav
August 24, 2025The DNA template is denatured using helicase is wrong statement about pcr because in denaturation high temp is enough to separate the strand
Khushi Agarwal
August 24, 2025The DNA template is denatured by heat not helicase.
karishma don
August 24, 2025the dna is denatured by using high temp not an helicase enzyme
Anurag Giri
August 24, 2025Ans 1 bcoz
PCR denatures DNA through high heat, not helicase
Aafreen Khan
August 24, 2025The DNA template is denatured using helicase is incorrect about PCR because PCR denatures DNA through high heat not by helicase
Dharmpal Swami
August 24, 2025Dna strand in PCR denatured by high temperature
Helicase not required for denaturing of strands
Aakanksha Sharma
August 24, 2025Option A is wrong bcz helicase is not required in denaturation but high temperature is require
Priyanka Choudhary
August 24, 2025The DNA template is denatured using helicase is wrong answer because the dna template is denature using heat not helicase
Karishma
August 24, 2025Option a is ans..
Dipti Sharma
August 24, 2025The DNA template is denatured using helicase is incorrect because in PCR high temperature is responsible for denaturation.
HIMANI FAUJDAR
August 24, 2025Ans correct answer is (a) No helicase enzyme is used for the Denaturation only high temperature used for denatured the strand.
Priya dhakad
August 24, 2025DNA strand denatured by high temperature not helicase enzyme .
AKANKSHA RAJPUT
August 24, 2025Ans 1 bcoz
PCR denatures DNA through high heat, not helicase
Divya Mandhania
August 24, 2025Dna template denatured using template is the incorrect so option a is correct
Santosh Saini
August 24, 2025In PCR DNA is denatures at the high temperature (95°) , not helicase
Sneha Kumawat
August 24, 2025Pcr denature dna thorough heat not helicase
Heena Mahlawat
August 24, 2025No, helicase isn’t used to denature dna strands but high temperature is used
Tanvi Panwar
August 24, 2025DNA is not denatured using helicase but by high temperatures.
MOHIT AKHAND
August 24, 2025Done sir ✅
Ayush Dubey
August 24, 2025The DNA template is denatured using helicase.
Surbhi Rajawat
August 24, 2025In PCR denaturation of DNA happens due to temperature and not helicase. Hence A is helicase
Neelam Sharma
August 24, 2025The DNA template is denatured using helicase is incorrect because DNA template is denatured by 90° – 94° c
Aman Choudhary
August 24, 2025High temperature denatured the DNA template in PCR
Samiksha bajiya
August 24, 2025In PCR DNA denature at high temperature not in presence of helicase
Bhawna Choudhary
August 24, 2025Option A is incorrect
Bharti Yadav
August 24, 2025The DNA template is denatured using high temperature not helicase
Priyanka Verma
August 24, 2025correct option is A because for denaturation DNA needs high temperature not the helicase
Monika jangid
August 24, 2025Dna denature by heat not helicase
Varsha Tatla
August 25, 2025Option 1st will be incorrect
Divya rani
August 25, 2025In pcr denaturation of dna occurs at high temperature about 94-98°C and this temperature enough to break hydrogen bonding between two DNA strands .
Diksha Chhipa
August 25, 2025In pcr for denaturation we use high temp not helicase
shruti sharma
August 25, 2025The dna template denature using high temp
Payal Gaur
August 25, 2025A option is incorrect because high temperature required in denaturation of DNA ,not require helicase.
Minal Sethi
August 25, 2025DNA template is melted due to high temperature not because of helicase
Bhavana kankhedia
August 26, 2025The DNA template is denatured using helicase.
Bhavana kankhedia
August 26, 2025A option is incorrect because high temperature required in denaturation of DNA ,not require helicase
Surendra Doodi
August 26, 2025The DNA template is denatured using helicase are incorrect for denature use High temperature
Vanshika Sharma
August 26, 2025Ans is a bcz no enzyme like helicase is req to denature the dna template only high temp is sufficient to denature them
Manisha
August 26, 2025Done ✅
Shivani
August 26, 2025Option A is incorrect
Because in PCR high temp.is required for denaturing not helicase.
Rishita
August 26, 2025Opt a
Alec
August 26, 2025Option 1 is correct because DNA is denatured by giving 90- 95 degree celsius temperature.
Pallavi Ghangas
August 26, 2025In PCR strands are separated by temperature and not Helicase
Simran Saini
August 26, 2025The DNA template is denatured using helicase.
Sakshi Kanwar
August 27, 2025DNA is denatured by high temperature in PCR it’s does not require helicase
Muskan singodiya
August 28, 2025Dna denatured high temp. Not helicase
Kanica Sunwalka
August 28, 2025high temp is used to brk h bonds
Nilofar Khan
August 28, 2025Option a is incorrect
A.The DNA template is denatured using helicase.
Deepika Sheoran
August 28, 2025Option A is correct
The DNA Template is Denaturated using Helicase. High temperature is given to denatured the template DNA..
Kajal
August 28, 2025In PCR no helicase is required for DNA denaturation here the denaturation is done by heating upto 98degree celcius
Neeraj Sharma
August 28, 2025Helicase does not play any role in pcr hence option A
Anisha Beniwal
August 28, 2025Option A is correct
Mitali saini
August 29, 2025Correct Answer: ✅ (a) The DNA template is denatured using helicase.
Parul Yadav
August 29, 2025During Denaturation step of PCR double strands of DNA are separated by high heat not by the helicase enzyme .
Asha Gurzzar
August 30, 2025High temperature needed to melt dna in pcr, not helicase so a is incorrect
Khushi Singh
August 30, 2025Helicase used for unbinding of Dna but don’t not use in pcr due to low melting point
Sonam Saini
August 30, 2025डीएनए टेंपरेट को हेलीकेस का उपयोग करके विकृत किया जा सकता है
Kirti Agarwal
August 31, 2025The DNA template is denatured using helicase
Palak Sharma
August 31, 2025In pcr for denaturation we use high temp not helicase
Kajal
August 31, 2025Correct Answer is (a) The DNA template is denatured using helicase
Aartii sharma
August 31, 2025(a)the dna template is denatured using helicase
Konika Naval
August 31, 2025The DNA template is denatured using helicase
Meenakshi Choudhary
September 3, 2025The DNA template is denatured using helicase option a is correct
Muskan Yadav
September 8, 2025The DNA template is denatured using helicase.