Gene Expression Calculators

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Gene expression is the process by which information encoded in a gene is converted into a functional product — most commonly a protein, or functional RNA (rRNA, tRNA, miRNA). The central dogma: DNA → (transcription) → RNA → (translation) → protein. In eukaryotes, transcription occurs in the nucleus, producing pre-mRNA that is processed (5' capped, spliced, polyadenylated) before export to the cytoplasm for translation. Gene expression is regulated at multiple levels — promoter accessibility, transcription factor binding, mRNA stability, and translation efficiency — allowing each cell type to express only relevant genes. RT-qPCR and RNA-seq are the primary methods for measuring gene expression levels.

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Steps of Gene Expression

  1. Transcription: RNA polymerase II binds promoter with transcription factors → synthesizes pre-mRNA
  2. RNA processing: 5' cap + poly-A tail + splicing (intron removal by spliceosome)
  3. Export: mature mRNA exits nucleus through nuclear pore
  4. Translation: ribosome assembles at AUG start → tRNAs bring amino acids → chain elongation → stop codon → release
  5. Post-translational modification: folding, phosphorylation, glycosylation

Regulation Levels

Transcriptional: TF binding to promoters/enhancers; chromatin remodeling (histone acetylation = open; methylation = closed). Post-transcriptional: miRNA → RISC → mRNA degradation or translational repression; alternative splicing. Epigenetic: DNA methylation at CpG sites silences genes; heritable through cell division.

Measurement

RT-qPCR: sensitive; single gene; 2^(−ΔΔCt) quantification. RNA-seq: whole transcriptome; DESeq2/edgeR for differential expression.

Glossary

Gene Expression
Conversion of DNA genetic information into functional RNA and protein via transcription (DNA→RNA) and translation (mRNA→protein); regulated at multiple levels to enable cell type-specific gene activity.
Transcription
Synthesis of RNA from a DNA template by RNA polymerase; in eukaryotes pre-mRNA is processed (5' cap, splicing, poly-A tail) in the nucleus before export for translation.
RT-qPCR
Reverse transcription quantitative PCR; measures mRNA abundance; steps: RNA extraction → reverse transcription → qPCR; relative quantification by 2^(−ΔΔCt) normalized to a reference gene.

Frequently Asked Questions

Gene expression converts genetic information from DNA into functional protein through: (1) Transcription: RNA polymerase binds the promoter and synthesizes a complementary RNA strand. In eukaryotes pre-mRNA is produced in the nucleus and undergoes 5' capping, 3' polyadenylation, and splicing to produce mature mRNA. (2) Translation: ribosomes assemble at the AUG start codon; aminoacyl-tRNAs deliver amino acids according to codons; synthesis continues until a stop codon (UAA, UAG, UGA) is encountered. (3) Post-translational modification: folding, phosphorylation, glycosylation, signal sequence cleavage, and transport to the correct cellular location.

Gene expression is regulated at multiple levels: Transcriptional: transcription factors bind promoters and enhancers; chromatin remodeling (histone acetylation opens chromatin → active gene; histone deacetylation + methylation → closed chromatin → repressed). Post-transcriptional: alternative splicing (~95% of human multi-exon genes); mRNA stability (AU-rich elements control degradation); miRNA (~22 nt non-coding RNA) guides RISC to degrade or repress specific mRNAs. Translational: ribosome recruitment efficiency; IRES elements. Epigenetic: DNA methylation at CpG sites silences genes and is heritable through cell division — central to cell differentiation.

RT-qPCR (reverse transcription quantitative PCR) measures specific mRNA abundance. Steps: (1) RNA extraction with DNase treatment. (2) Reverse transcription: mRNA → cDNA. (3) qPCR: gene-specific primers amplify target cDNA; SYBR Green or TaqMan probe generates fluorescence each cycle. (4) Ct (cycle threshold): the PCR cycle at which fluorescence exceeds background — lower Ct = more starting mRNA. (5) Relative quantification: ΔΔCt method → fold change = 2^(−ΔΔCt) normalized to a reference gene (GAPDH, β-actin). Reference genes must be validated as stably expressed under experimental conditions.

RNA-seq (RNA sequencing) measures the entire transcriptome simultaneously using next-generation sequencing. Process: extract RNA → convert to cDNA library → sequence all fragments → align to reference genome → count reads per gene. Differential expression: DESeq2 or edgeR compare read counts between conditions to identify significantly changed genes. RT-qPCR vs. RNA-seq: RT-qPCR is targeted (specific genes known in advance), highly sensitive, cheap, fast, no bioinformatics needed. RNA-seq is discovery-based (no prior knowledge required), whole-transcriptome, requires bioinformatics, and is more expensive per sample. Typical workflow: RNA-seq for discovery → RT-qPCR to validate key findings.