Insertion Mutations and Reading Frame Shifts — NEET Biology
📚 Practice ConceptSimilarly, if we now insert two letters at the same place, say BI'. Now it would read,
Which of the following statements about DNA strands during transcription are NOT correct? S1: The strand that acts as a template for RNA synthesis has a 3'→5' polarity. S2: The coding strand is the DNA strand whose sequence is identical to the newly synthesized RNA, with the exception of thymine being replaced by uracil. S3: RNA polymerase reads the coding strand in a 5'→3' direction to synthesize RNA. S4: If both DNA strands were to act as templates simultaneously, it would lead to the formation of two RNA molecules with identical sequences. S5: The coding strand is identical in sequence to the template strand, only differing in the base thymine and uracil.
View solution & NCERT explanation
Correct answer: D — S3, S4, S5 only
The core concept is the distinction between template and coding strands of DNA and their roles in transcription. S1: Correct. NCERT states, "the strand that has the polarity 3'→5' acts as a template, and is also referred to as template strand." S2: Correct. NCERT states, "The other strand which has the polarity (5'→3' ) and the sequence same as RNA (except thymine at the place of uracil), is displaced during transcription. Strangely, this strand (which does not code for anything) is referred to as coding strand." S3: Incorrect. RNA polymerase reads the *template* strand in a 3'→5' direction. The coding strand is not read by RNA polymerase. NCERT states, "the DNA-dependent RNA polymerase also catalyse the polymerisation in only one direction, that is, 5'→3' ", referring to the direction of RNA synthesis, which implies reading the template 3'->5'. S4: Incorrect. If both strands act as a template, they would code for RNA molecules with *different* sequences, as they are complementary to each other, not identical. NCERT states, "if both strands act as a template, they would code for RNA molecule with different sequences (Remember complementarity does not mean identical)". S5: Incorrect. The coding strand and template strand are complementary to each other, not identical. For example, if one has A, the other has T (or U in RNA). Therefore, statements S3, S4, and S5 are NOT correct. Option D correctly identifies the incorrect statements. The question tests the understanding of the fundamental principles governing which DNA strand is transcribed and the implications of this process.
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Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
176/180MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.