Transcript analysis

Transcript analysis

Which method is not ideal to study tissue-specific protein-protein interaction?

Tissue-specific protein-protein interactions reflect context-dependent complexes regulating differentiation and signaling. Co-immunoprecipitation preserves native interactions by antibody capture of bait protein and associated partners from lysates, suitable for tissue extracts. RNA immunoprecipitation detects RNA-protein contacts. Western blot alone measures protein abundance but not interaction. Site-directed mutagenesis artificially introduces point mutations to test functional domains in recombinant systems, typically in heterologous cell lines, rather than probing endogenous interaction landscape across tissues. It assesses importance of residues but does not detect complexes directly, making it unsuitable as primary method for analyzing native protein-protein interactions.

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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Which method uses poly(A) tail as a handle to capture mRNA?

3 prime RACE aims to capture unknown downstream sequence extending to messenger RNA terminus. Most eukaryotic messenger RNAs possess post-transcriptional poly-adenine tail of 100-250 residues at 3 prime end added by poly-A polymerase, important for stability and translation. This homopolymeric feature serves as universal handle for selective priming. An oligo-dT primer containing adapter sequence anneals to poly-A tail during reverse transcription, enabling synthesis of complementary DNA spanning entire 3 prime untranslated region. Subsequent PCR amplification using gene-specific forward primer and adapter reverse primer amplifies unknown region between known sequence and poly-A junction.

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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Which of the following sequences is expected to form most stable hybridization?

Hybridization stability depends on chemical composition and physicochemical environment. Guanine-cytosine pairs contain three hydrogen bonds versus two for adenine-thymine, and stronger base-stacking interactions, conferring higher thermodynamic stability and elevated melting temperature. Elevated monovalent cation concentration, such as high salt, stabilizes duplex by shielding electrostatic repulsion between negatively charged phosphate backbones. High temperature destabilizes mismatched duplexes but GC-rich sequences retain annealing due to greater enthalpy. Therefore combination of GC-rich sequence with high salt maintains most stable hybrid despite thermal stress, whereas AT-rich or low salt conditions favor dissociation.

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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The presence of a “super-shifted” band in EMSA indicates:

Supershift assay extends conventional EMSA to identify specific protein within DNA-protein complex. Binding reaction initially shows retarded band corresponding to protein-DNA interaction. Addition of antibody specific to suspected transcription factor binds exposed epitope of protein while still attached to DNA, forming ternary antibody-protein-DNA complex of even larger size and more positive charge. Consequently electrophoretic mobility decreases further, producing super-shifted band migrating above original shift near well. Control immunoglobulin lacking specificity does not produce this additional retardation. Supershift therefore confirms identity of DNA-binding protein and demonstrates protein participation in specific complex formation.

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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Which enzyme digests methylated parental DNA in inverse PCR?

Parental plasmids propagated in most Escherichia coli strains are methylated by Dam methyltransferase at N6 position of adenine within sequence GATC. After inverse PCR mutagenesis, mixture contains both methylated wild-type template and unmethylated mutated amplicon. Selective removal of parental background exploits methylation sensitivity. DpnI specifically recognizes GATC only when adenine is methylated, introducing double-strand breaks and fragmenting template into non-functional pieces. Newly amplified mutated DNA lacking methylation resists digestion and remains intact for transformation. This enzymatic selection dramatically improves efficiency, explaining why DpnI treatment is indispensable for site-directed mutagenesis protocols.

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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Inverse PCR mutagenesis includes:

Inverse polymerase chain reaction based mutagenesis allows mutation of entire plasmid without subcloning. Divergent primers containing desired change amplify around circular template generating linear mutated product. Reaction mixture retains original non-mutated parental plasmid isolated from methylation-competent Escherichia coli, which could transform and cause background wild-type colonies. DpnI is a restriction endonuclease that recognizes methylated and hemimethylated sequence 5 prime GATC methylated at adenine by Dam methylase. It cleaves parental methylated DNA into fragments unable to replicate, enriching for newly synthesized unmethylated mutated plasmid, increasing mutagenesis efficiency and reducing false positives.

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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Which mutagenesis technique involves using primers with the mutation?

Site-directed mutagenesis introduces defined nucleotide changes at predetermined position to assess functional impact on protein or regulatory element. Methodology employs synthetic oligonucleotide primers that are complementary to target plasmid except for desired substitution, insertion, or deletion in central region. These mismatched primers anneal during polymerase chain reaction amplification, incorporating mutation into newly synthesized strands. Resulting plasmids carry mutation and are selected after digestion of methylated parental template. Random mutagenesis creates unpredictable changes, while EMSA and footprinting assay DNA binding, not generate mutations. Therefore primer-directed approach provides precision for structure-function analysis.

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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Which immunoprecipitation technique is used for RNA-protein interactions?

Immunoprecipitation approaches dissect nucleic acid-protein interactions. Chromatin immunoprecipitation targets DNA bound by proteins in cross-linked chromatin, useful for transcription factors and histones. Co-immunoprecipitation precipitates protein complexes to identify protein-protein partners. Immunoprecipitation of RNA-associated complexes using generic antibodies lacks nucleic acid specificity. RNA immunoprecipitation is dedicated to RNA-binding proteins; cells are cross-linked or used native, lysed, and specific antibody against RNA-binding protein enriches messenger RNAs, micro RNAs, long non-coding RNAs bound in vivo. Associated RNAs are isolated, purified, and identified by RT-PCR or RNA-seq, revealing post-transcriptional regulatory networks.

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 key distinguishing factor between SAGE and CAGE?

Serial Analysis of Gene Expression and Cap Analysis of Gene Expression both generate short tags for sequencing, yet differ fundamentally in biological focus. SAGE isolates tags from internal position after NlaIII cleavage, providing quantitative estimate of messenger RNA abundance regardless of transcript termini, often representing internal coding sequence. CAGE specifically captures 5 prime capped ends by biochemical selection of 7-methylguanosine, sequencing 20-27 base adjacent to transcription start site. Consequently, CAGE precisely maps transcription start sites and promoter usage, whereas SAGE enumerates gene expression levels without start site accuracy, reflecting distinction centered on cap structure.

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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In ChIP, which is precipitated?

Chromatin immunoprecipitation investigates in vivo association of proteins with genomic DNA. Living cells are treated with formaldehyde, which cross-links proteins to DNA and proteins to proteins preserving physiological interactions. Chromatin is sheared by sonication or enzymatic digestion into 200-500 base fragments. An antibody specific to transcription factor, histone modification, or cofactor immunoprecipitates cross-linked chromatin, enriching bound DNA fragments. After reversal of cross-links and protease digestion, recovered DNA is analyzed. Thus final immunoprecipitate comprises protein-DNA complex, not naked DNA or RNA alone, reflecting chromatin context and occupancy.

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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Which of the following is most useful for analyzing gene regulation via DNA-binding proteins?

Gene regulation often involves sequence-specific DNA-binding proteins such as transcription factors and repressors interacting with cis-regulatory elements. DNase I footprinting directly visualizes interaction by protecting DNA backbone from nuclease cleavage where protein bound, leaving gap in cleavage ladder that maps binding motif at nucleotide resolution. Northern blotting measures transcript size and abundance, 5 prime RACE clones untranslated ends, and S1 mapping quantifies protected fragments; all focus on RNA rather than protein-DNA contact. Therefore footprinting provides mechanistic insight into regulatory protein occupancy, essential for studying transcriptional control and enhancer 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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Which method enables transcriptome-wide expression profiling?

Transcriptome-wide expression profiling demands technology capable of unbiased, high-throughput measurement across all transcripts present in cell. RNA-seq achieves this by massive parallel sequencing of complementary DNA libraries, yielding digital counts proportional to RNA abundance, enabling detection of differential expression, splicing, and novel isoforms genome-wide. EMSA and footprinting analyze protein-DNA binding at single locus level. RT-PCR quantifies few genes but lacks global scope. Only RNA-seq provides simultaneous interrogation of thousands of genes without requiring prior probe design, revolutionizing functional genomics and systems biology approaches.

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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