4. Which radioisotope isgenerally incorporated in thymine to studyDNA replication process?
(1) 32p (2) 35S
(3)3H (4) 14C
Introduction
Studying DNA replication requires precise labeling of newly synthesized DNA to track replication dynamics, timing, and localization. One common approach involves incorporating radiolabeled nucleotides into DNA. Among the radioisotopes used, tritiated thymidine (^3H-thymidine) is widely employed to label thymine residues specifically during DNA synthesis. This article explains why ^3H-thymidine is generally chosen, how it works, and compares it with other radioisotopes.
Why Label Thymine?
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Thymine is a DNA-specific base, absent in RNA, making it an ideal target for DNA-specific labeling.
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Incorporation of labeled thymidine into DNA allows selective detection of DNA synthesis without labeling RNA.
Common Radioisotopes Used in DNA Labeling
| Radioisotope | Common Use in DNA/RNA Labeling | Characteristics |
|---|---|---|
| ^3H (Tritium) | Incorporated into thymidine for DNA labeling | Emits low-energy beta particles; ideal for autoradiography; sensitive and specific |
| ^32P (Phosphorus-32) | Labels phosphate backbone of nucleotides | High-energy beta emitter; used in DNA sequencing and labeling nucleotides |
| ^35S (Sulfur-35) | Labels sulfur-containing molecules (e.g., proteins) | Not used for thymine labeling; mainly for proteins |
| ^14C (Carbon-14) | Labels carbon atoms in nucleotides | Longer half-life; less commonly used for thymine due to lower sensitivity |
Why ^3H-Thymidine Is Preferred for DNA Replication Studies
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Specificity: ^3H-thymidine is incorporated only into DNA, not RNA, providing clear evidence of DNA synthesis.
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Sensitivity: The low-energy beta emissions from tritium allow for high-resolution autoradiography.
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Historical Precedence: Since the 1950s, ^3H-thymidine has been the gold standard for labeling DNA in replication studies.
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Compatibility: It integrates naturally during DNA synthesis without significantly affecting DNA structure or function.
How ^3H-Thymidine Labeling Works
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Cells or in vitro systems are supplied with ^3H-thymidine.
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DNA polymerases incorporate ^3H-thymidine into newly synthesized DNA strands.
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After incubation, DNA is extracted, and autoradiography detects the radioactive signal.
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The distribution and intensity of the signal reflect DNA replication activity.
Comparison with Other Radioisotopes
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^32P: Labels phosphate groups in nucleotides; used for labeling entire nucleotide pools but not specific to thymine.
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^35S: Used mainly for labeling proteins, not DNA.
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^14C: Used in some studies but less sensitive and requires longer exposure times.
Summary
| Radioisotope | Best Use for DNA Replication Labeling | Reason for Use |
|---|---|---|
| ^3H (Tritium) | Labeling thymine in DNA | Specific, sensitive, widely used |
| ^32P | Labeling phosphate backbone | Less specific for thymine |
| ^35S | Protein labeling | Not used for DNA |
| ^14C | General nucleotide labeling | Less sensitive, longer half-life |
Conclusion
The radioisotope ^3H (tritium) incorporated into thymidine is generally used to study DNA replication by labeling thymine residues. Its specificity for DNA, sensitivity in detection, and established use in autoradiography make it the preferred choice over other isotopes.
Answer:
The radioisotope generally incorporated in thymine to study DNA replication is (3) ^3H (Tritium).
33 Comments
Manisha choudhary
July 25, 2025🔥🔥🔥🔥🔥done sir
Varsha Tatla
August 3, 20253H tritiam
Diksha chhipa
July 29, 20251H3 is preferred for dna rep because it can be incorporated only in dna not in rna.so it is specific .low energy beta emission.and it incorporated naturally during dna synthesis without affecting its structure.
Pratibha Sethiya
July 29, 2025Correct option is option (3)
Thymine is a nitrogen base found only in DNA (not in RNA).
The best way to label thymidine is using 3H (tritium) — a radioactive hydrogen. Bcz it is specific, it’s sensitivity in detection , it integrated naturally without affecting it’s structure & function
In other options
32P- labels the phosphate group, not specific to thymine.
35S- used to label proteins (because sulfur is in amino acids like cysteine, not in DNA).
14C – general nucleotide labelling, less specific
anurag giri
July 29, 2025Ans is 3 bcoz it has Incorporated into DNA during replication; used to track synthesis and it is emit low energy beta particle
Vanshika Sharma
July 29, 2025Ans is 3 bcoz it is incorporated into dna during replication,not in rna so it’ is specific
Surbhi Rajawat
July 29, 2025To label thymine we label it with tritium which is an isotope of hydrogen. So the answer is 3
Priya Khandal
July 29, 20253 answer h3
Khushi Mehra
July 29, 2025Answer is 3
Tritium , an isotope of hydrogen specifically used for detection of DNA synthesis not for RNA .
Heena
July 29, 2025In thymidine (nucleoside)-tritium(H^3)is incorporated in place of hydrogen which is radio labelled and helps to study dna replication process …and thymine is labelled due to the fact that it is present only in dna not rna .
Priti Khandal
July 29, 2025To label thymine we label it with tritium which is isotope of hydrogen and answer is 3 H3
shruti sharma
July 29, 2025ANS IS thymide incorporated for dNA label
thymide found in dna not in rna
Niti tanwar
July 29, 2025The redioisotop is generally incorporated into thymidine to study dna replication. Is ^3H (tritium).
Payal Gaur
July 30, 2025For study of DNA replication H3(tritium) radioisotope is incorporated in Thymine. And Thymine present in DNA not in RNA
Priyanka choudhary
July 29, 2025Correct answer is option 3(H3),
Because yeh DNA replication m thymidine ko track krta hai and radiolabling me bhi useful hai
Sneha Kumawat
July 30, 2025Answer is H3
Dipti Sharma
July 30, 2025tritium which is an isotope of hydrogen is generally used to label thymine so ,the answer is 3.
Reply
Deepika Sheoran
July 30, 2025Answer is 3
Dna replication H3(tritium) Radioisotope is incorporated in thymine.
Dna present in thymine.
Anjani sharma
July 30, 2025Answer 3 as it is specific and incorporated into thymine
Khushi Vaishnav
July 30, 2025Correct option is option 3 , because
Thymine is a nitrogen base found only in DNA not in RNA .
Rakesh Dhaka
July 30, 2025Correct option is 3 bcz thymine present in dna not rna
Dharmpal Swami
July 30, 2025H3 radioisotope is generally incorporate in thymine to study dna replication
Komal Soni
July 30, 2025The radioisotope ^3H (tritium) incorporated into thymidine is generally used to study DNA replication by labeling thymine residues. Thymine found only in DNA, sensitivity in detection, and established use in autoradiography make it the preferred choice over other isotopes.
P whole DNA & RNA ka backbone he. Specific nahi
Aman Choudhary
July 30, 2025Option 3 is correct H3 incorporated in thymine
Anisha jakhar
July 31, 2025Option 3 is the correct answer
Shivani
July 31, 2025Done 👍 sir…
Varsha tatla
August 2, 20253h’radioisotope use for thymine labelling bcz thymine contain only dna nit rna so,it is useful for detection
14c use for labelling nucleotide
35s use for protien
34p use for phosphate group of nucleotide
Varsha tatla
August 2, 20253h’radioisotope use for thymine labelling bcz thymine contain only dna nit rna so,it is useful for detection
14 c use for labelling nucleotide
35 S use for protien
34 p use for phosphate group of nucleotide
Mahima Sharma
August 2, 20253H thymidine
Anita Choudhary
August 28, 2025Correct answer is 3-3H thymidine
Alec
August 30, 2025correct ans. is 3 – 3H is incorporated into thymine.
Aakansha sharma Sharma
September 20, 2025Answer 3 as it is specific and incorporated into thymine
Deepika Sheoran
November 6, 2025DNA replication H-3 (tritium) Radioisotope is incorporated in thymine.
DNA present in thymine.