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#RNA synthesis

14 public questions tagged with this topic.

CHEMISTRY

Which enzyme synthesizes RNA from a DNA template?

RNA polymerase catalyzes transcription, synthesizing RNA by reading the DNA template strand in the 3’ to 5’ direction. This follows from latest NCERT 2026-27 principle explaining the concept clearly for NEET students in simple steps as per rationalized syllabus.

Ref: NCERT Chemistry Textbook - Latest Edition for Academic Session 2026-27 (Rationalized Textbook for Class XI and XII)Topic: Mole concept, atomic structure, chemical formulas like H₂O, CO₂, CH₃CH₂NH₂ and periodic trends.

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Transcription in Eukaryotes

Sensitivity of RNA polymerases to α-amanitin is

Sensitivity to alpha-amanitin toxin distinguishes three nuclear polymerases and is exploited in nuclear run-on assays. Pol II shows highest sensitivity, IC50 approximately 0.01 microgram per milliliter, blocked by binding near bridge helix. Pol III requires about ten micrograms per milliliter, intermediate sensitivity, while Pol I remains active even at hundreds of micrograms per milliliter, classified as resistant. Ranking therefore Pol II greater than Pol III greater than Pol I. Structural divergence in funnel domains and trigger loop residues that contact bicyclic peptide explains different

Ref: Berg et al., Biochemistry, 9th ed., Chapter 28: Sensitivity II > III > I; Alberts et al., Molecular Biology of the Cell, Amanitin sensitivity ranking

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Transcription in Eukaryotes

α-amanitin strongly inhibits

Alpha-amanitin cyclic octapeptide from Amanita phalloides death cap mushroom penetrates hepatocytes and binds with extremely high affinity in funnel and trigger loop beneath RNA polymerase II active site, obstructing translocation and nucleotide incorporation, leading to slow elongation arrest and degradation of RPB1 subunit. RNA polymerase II is most sensitive with inhibition constant around ten nanomolar, blocked at one microgram per milliliter, causing fatal liver failure. Polymerase III requires tenfold higher concentration, while polymerase I and mitochondrial polymerase resist up to high

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: alpha-amanitin strongly inhibits Pol II; Berg et al., Biochemistry, Amanitin mechanism

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Transcription in Prokaryotes

Abortive initiation refers to synthesis of RNA of length

During initial transcription, RNA polymerase undergoes iterative cycles of synthesizing and releasing short RNAs while remaining bound to promoter. Structural blockage occurs because sigma factor region 3.2 loop threads through RNA exit channel, obstructing extension beyond about nine to ten nucleotides. Polymerase synthesizes short oligoribonucleotides two to nine bases that escape into environment as abortive transcripts before productive escape. These ≤10 nucleotide products characteristic of abortive initiation phase. Overcoming this barrier requires conformational change displacing sigma

Ref: Watson et al. Chapter 13: Abortive initiation RNA length ≤10 nucleotides; Alberts Chapter 6 Abortive transcripts initiation complex instability

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Transcription Basics

RNA polymerase synthesizes RNA slower than DNA polymerase because

Bacterial RNA polymerase elongates roughly 40-50 nucleotides per second, significantly slower than DNA polymerase III synthesizing DNA near 750-1000 nucleotides per second during replication. Reduced rate attributed to lower processivity because transcription includes frequent pausing, backtracking for proofreading via GreA/GreB, waiting for regulatory factors like NusA, and requirement to unwind DNA continuously. Replication utilizes sliding clamp beta conferring high processivity and topoisomerases cooperating efficiently. Transcriptional pausing facilitates coupling with translation, co-tra

Ref: Berg Biochemistry Chapter 28: Transcription rate slower than replication processivity; Watson Chapter 13 Elongation speed comparison

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Transcription Basics

Transcription does not require which of the following?

DNA polymerases initiate synthesis only from provided primer supplying 3' hydroxyl because they cannot stabilize initial dinucleotide. RNA polymerase overcomes this through additional contacts: sigma factor, downstream DNA binding, and ability to hold two initiating ribonucleoside triphosphates base-paired to template at transcription start site via base stacking and hydrogen bonds. First phosphodiester bond forms de novo without prior polymer. This primer independent initiation permits transcription to start at defined +1 sites throughout genome. Consequently DNA template, Mg2+, and rNTPs suf

Ref: Alberts Molecular Biology of Cell 7th ed. Chapter 6: De novo initiation without primer; Lehninger Chapter 26 Transcription requirements primer independence

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Transcription Basics

RNA synthesis during transcription occurs in which direction?

Chain growth polarity dictated by chemistry of polymerase active site containing two magnesium ions. Nucleophilic attack by 3' hydroxyl of nascent RNA on alpha phosphate of incoming nucleoside triphosphate extends chain toward distal 5' to 3' direction. Polymerase simultaneously translocates downstream along antiparallel template reading 3' to 5', preserving RNA-DNA hybrid of eight to nine bases. Because synthesis requires free 3' OH, direction fixed unidirectionally analogous to DNA polymerases. This polarity ensures nascent RNA emerges 5' end first from exit channel while template entry dete

Ref: Berg Biochemistry 9th ed. Chapter 28: RNA synthesis 5' to 3' direction mechanism; Watson Chapter 13 Polarity

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