Hybridization

Hybridization

TEV protease in TAP recognizes:

Tobacco Etch Virus protease exhibits stringent specificity for seven amino acid consensus motif Glu-Asn-Leu-Tyr-Phe-Gln-Gly or Ser, cleaving between glutamine and glycine or serine residues. This extended recognition ensures minimal off-target cleavage within mammalian proteins, making it ideal for selective release of protein complexes during Tandem Affinity Purification. Recognition sequence is incorporated between two affinity tags in TAP construct. ATG represents translation initiation codon, calmodulin site binds calcium-dependent calmodulin, and Protein A motif binds immunoglobulin. Seven-residue specificity underlies its utility as biotechnological tool for precise proteolysis.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

Which method enables studying multiple protein interactions at once?

Protein microarray format enables simultaneous evaluation of thousands of interactions on single slide, providing high-throughput advantage over pairwise methods. By immobilizing purified proteins, antibodies, or peptides in arrayed spots, one incubation with labeled probe reveals many binding events in parallel, detecting protein-protein, protein-DNA, protein-lipid, or antibody-antigen interactions. Pull-down, electrophoretic mobility shift assay, and RT-PCR are low-throughput or targeted approaches. Microarray multiplexing drastically reduces sample, time, and reagent consumption, facilitating proteome-scale network mapping, biomarker profiling, and drug screening under standardized experimental conditions.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

Which hybridization technique uses fluorophore-tagged oligonucleotides?

Fluorescence In Situ Hybridization employs short oligonucleotide probes covalently conjugated with fluorophores such as FITC, Cy3, or Texas Red that hybridize specifically to complementary DNA or RNA sequences in fixed chromosomes, interphase nuclei, or tissue sections. Hybridization signal visualizes genomic loci, copy number alterations, translocations, or gene expression patterns under fluorescence microscopy. SPR detects refractive index shifts, electrophoretic mobility shift assay evaluates protein-DNA binding by gel retardation, and ROTA assesses transcription rate. FISH combines molecular hybridization specificity with fluorescence detection providing spatial resolution in cytogenetics research.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

What is the final stage in SPR interaction study?

Complete Surface Plasmon Resonance interaction cycle comprises ligand immobilization, baseline stabilization, analyte association, dissociation with buffer wash, and final regeneration to strip residual bound analyte while preserving ligand functionality. Regeneration restores baseline resonance units using mild regeneration buffers, enabling reuse of same chip for multiple concentration injections and kinetic replication. Analysis, dissociation, and calibration are intermediate steps, but regeneration represents definitive concluding stage preparing surface for next cycle. Optimization prevents ligand denaturation and ensures consistent binding capacity across experiments, critical for high-quality kinetic and affinity measurements.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

In SPR, what must be immobilized first?

In Surface Plasmon Resonance workflow, ligand must be covalently or non-covalently immobilized first onto dextran or gold surface of sensor chip to establish stable baseline. Immobilization chemistry may use amine coupling, thiol, streptavidin-biotin, or antibody capture, optimizing orientation and activity. Only after ligand immobilization and blocking of residual sites does analyte injection occur, allowing measurement of binding kinetics. Probe, analyte, and substrate denote soluble interaction partners or downstream molecules, not the initially attached species. Correct order of steps is critical for reproducible kinetic evaluation and regeneration cycles.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

What is the principle of pull-down assay?

Principle of pull-down assay centers on affinity binding between tagged bait protein and immobilized ligand, enabling capture of interacting prey proteins from mixture. Bait is expressed as fusion with GST, His, biotin, or Flag tag and retained on corresponding resin. Incubation with cell lysate allows physiological binding partners to co-precipitate via non-covalent interactions. After washing non-specific proteins, complex is eluted and analyzed by SDS-PAGE, Western blot, or mass spectrometry. Method does not depend on temperature-sensitive dyes, fluorescent resonance energy transfer, or radioactive labeling, but on highly specific tag-ligand affinity chemistry.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

Which technique can study RNA polymerase activity from cut templates?

Run-off transcription assay is uniquely suited to study RNA polymerase activity using linear DNA templates cut downstream of promoter, causing polymerase to transcribe and then dissociate at cut end, producing defined-length runoff transcript. By varying template truncation, promoter mutations, or adding transcription factors, investigators dissect initiation, elongation efficiency, and termination. Northern blot detects steady-state RNA, electrophoretic mobility shift assay measures DNA-protein binding, and RT-PCR quantifies RNA abundance, but none directly monitors active transcription from defined ends. Run-off system provides quantitative, controlled in vitro readout of polymerase function.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

Which tag is commonly used in TAP for high-purity complex isolation?

Tandem Affinity Purification relies on Calmodulin Binding Peptide or CBP as second affinity module for high-purity complex isolation under near-physiological conditions. CBP binds calmodulin resin in calcium-dependent manner after first purification on IgG Sepharose and TEV cleavage. Calcium chelation with EGTA allows gentle elution preserving native complexes for downstream mass spectrometry. TRITC is fluorescent dye, biotin requires streptavidin matrix, and GFP is reporter for localization, not an affinity handle in classic TAP design. CBP provides low background and reversible binding essential for sequential purification strategy maximizing purity.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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What is the main objective of in vitro mutagenesis?

In vitro mutagenesis is a reverse genetics strategy aimed at generating defined nucleotide changes in cloned genes to investigate relationship between protein primary structure and biological function. By altering specific codons corresponding to active site residues, binding motifs, or structural domains, researchers evaluate effects on catalysis, stability, interaction, or localization. Results link sequence to function, guiding enzyme mechanism analysis and rational protein engineering. Objective is not to measure transcription rate, discover unknown genes randomly, or simply amplify DNA. Controlled mutagenesis provides mechanistic insights central to molecular biology, biochemistry, and biotechnology applications.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

In inverse PCR, DpnI is used to:

In inverse PCR-based site-directed mutagenesis, DpnI endonuclease plays crucial role in selection of newly synthesized mutant plasmids. DpnI specifically recognizes methylated GATC sequences, which occur frequently in parental plasmid DNA propagated in dam+ E. coli strains. Unmethylated PCR product carrying mutation is resistant to DpnI cleavage, whereas methylated parental strands are digested into fragments. This selective removal enriches mutant clones and reduces background wild-type colonies after transformation. DpnI does not cleave mutant DNA, synthesize RNA, or ligate fragments; its function is methylation-dependent restriction for background elimination.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

What is the final PCR product when Q1-Q3 and Q2-Q4 are used with mutations?

During two-step overlap extension mutagenesis, initial PCR reactions Q1 with Q3 and Q2 with Q4 generate overlapping fragments each carrying introduced mutation via internal primers. Denaturation and annealing of these fragments allow overlapping mutated region to hybridize, extending to form full-length template. Final amplification with only flanking primers Q1 and Q4 yields 1 kb product containing desired mutations at both targeted sites, while wild-type parental template remains largely undigested or removed by DpnI treatment. Shorter products like 700 bp or 0.5 kb would indicate incomplete fusion or nonspecific amplification, not successful mutagenesis.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

In a site-directed mutagenesis, Q2 and Q3 primers contain:

In overlap extension site-directed mutagenesis, primers Q2 and Q3 are internal mutagenic primers designed to be complementary to each other and harbor desired nucleotide substitution, insertion, or deletion at central position. They anneal to opposite strands of template and introduce specific mutation during first-round PCR amplifications generating two half fragments. These primers do not encode exon deletions, epigenetic modifications, or ligand moieties. Their overlapping mutated region allows subsequent fusion PCR with flanking primers Q1 and Q4 to produce full-length product carrying targeted change, enabling precise protein engineering studies.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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