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#transcriptome analysis

3 public questions tagged with this topic.

Sequencing

Which method uses poly-A tail for mRNA enrichment?

Mammalian messenger RNAs are modified with a 3' polyadenosine tail of 100 to 250 nucleotides added post-transcriptionally. Exploiting this feature, poly-T selection uses paramagnetic beads conjugated with oligo-dT sequences that base-pair with poly-A tails under high salt conditions. Non-polyadenylated rRNA and tRNA fail to bind and are washed away, enriching mRNA fraction for library preparation. This approach is essentially an affinity chromatography strategy based on A-T hybridization. Hydrolysis degrades RNA randomly, size exclusion separates by length without specificity, whereas poly-T selection provides mRNA specificity.

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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Transcript analysis

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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Transcriptome analysis

Which technique would best identify more than 1000 differentially expressed genes in one test?

A transcriptome microarray, also called expression array, contains probes for all annotated genes or entire transcriptome represented as tens of thousands of spots on a chip. Single hybridization of labeled cDNA from experimental and control samples allows parallel assessment of expression differences. Statistical analysis identifies hundreds to thousands of differentially expressed genes by fold change and p-value. RAPD assesses DNA polymorphism, genome sequencing determines DNA sequence rather than expression levels, and ChIP assesses protein-DNA interactions, making them unsuitable for simultaneous high-throughput quantification of over a thousand expression changes.

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.

View Details