12 public questions tagged with this topic.
An enhancer is a DNA sequence that increases transcription levels when bound by transcription factors.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Regulation of Gene Expression - Lac Operon
AraC protein embodies remarkable dual regulatory function determined by arabinose-dependent conformational switch. Polypeptide of 292 residues contains N-terminal dimerization and arabinose-binding domain linked via flexible interdomain arm to C-terminal DNA-binding domain possessing two helix-turn-helix motifs. Apo form without arabinose favors interaction binding to distal O2 operator and I1 half-site forming DNA repression loop that blocks polymerase. Arabinose-bound form reorganizes N-terminal arm, neutralizes arm dimer interactions, shifts DNA-binding specificity to adjacent I1-I2 half-sites upstream of PBAD, and exposes activation surface capable of direct contacts with RNA polymerase alpha subunit, behaving simultaneously as both repressor and activator depending on ligand status.
Ref: L-arabinose operon review – AraC is dual activator-repressor; apo-AraC loops araI1-O2 (210 bp) to repress.
Among general Pol II factors, TFIIH alone possesses ATP-dependent DNA helicase activity essential for promoter opening. Complex composed of ten subunits includes XPB ERCC3 translocase with 3' to 5' helicase that pumps downstream DNA toward polymerase, generating torsional stress to melt eleven to fifteen base pairs around transcription start site. XPD ERCC2 helicase participates primarily in nucleotide excision repair. Helicase action requires ATP hydrolysis and is inhibited by triptolide anticancer drug. TFIIH entry after Pol II-TFIIF completes preinitiation complex assembly enabling open complex formation.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: TFIIH helicase melts promoter DNA; Alberts 7th ed., General transcription factors TFIIH function
TBP saddle inserts into minor groove of eight base pair TATA box, using four phenylalanine side chains to intercalate between base steps, causing severe kinking of about eighty degrees toward major groove and slight unwinding. Such dramatic bending partially unwinds DNA, widens minor groove, and creates platform for TFIIA and TFIIB entry. Bending also brings upstream regulatory regions closer to initiation site and introduces strain facilitating promoter melting by TFIIH helicase. Crystallography of TBP-TATA shows twofold symmetric bending creating almost right angle conformation.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: TBP bends DNA ~80 degrees; PDB 1CDW TBP-TATA structure
TATA-binding protein functions within multisubunit TFIID complex comprising TBP plus thirteen to fourteen TBP-associated factors TAF1 to TAF14 forming lobe-like structures visible by electron microscopy. TFIID is first general transcription factor to bind core promoter, recognizing TATA box via TBP, initiator via TAF1 and TAF2, downstream promoter element via TAF6 and TAF9. TFIIA stabilizes TFIID-DNA interaction while TFIIB joins. Formation of TBP-TFIID promoter complex is rate-limiting step regulated by activators, coactivators like Mediator, and chromatin remodeling events controlling polymerase recruitment.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6: TFIID contains TBP and TAFs; Lodish 9th ed., Assembly of Pol II preinitiation complex
TBP abbreviates TATA-box binding protein, a twenty-seven kilodalton highly conserved universal transcription factor with saddle-shaped twofold symmetry, binding DNA as monomer. It inserts conserved phenylalanine residues into minor groove of TATA box, deforming DNA and providing landmark for preinitiation complex assembly. Present in TFIID for Pol II, SL1 for Pol I, and TFIIIB for Pol III, making it central to all three nuclear polymerase systems. TBP interacts with TFIIA, TFIIB, TAFs, and activators, nucleating transcription complex formation and promoter selection.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: TBP is component of all polymerase complexes; Alberts, Structure of TBP-DNA complex
IRFs, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.
Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)
Ci, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.
Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)
CSL/RBPJ, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.
Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)
Elk-1, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.
Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)
Go with C — Transcription factor. Under Ethylene, this is the standard explanation you’d use in class: it names the real driver or definition, while the rest are nearby but wrong. Not these: A) Kinase; B) Receptor; D) Transporter. When two options sound similar, choose the one that matches the textbook definition most tightly.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.
GA-MYB (C) is correct here. This is core Gibberellins: once you know the definition or pathway step, GA-MYB is the clear fit. The wrong ones are A) ARF; B) HY5; D) PIF. If the topic is about gradients or potentials, water/solutes move from higher to lower of the relevant quantity.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.
