| Criteria | DNA Synthesis (Replication) | RNA Synthesis (Transcription) | Remarks |
| Definition | Process by which a cell makes an exact copy of its entire DNA before cell division | Process by which a segment of DNA is transcribed into RNA | DNA synthesis ensures genetic continuity; RNA synthesis facilitates gene expression. |
| Primary Purpose | To duplicate the entire genome for inheritance during cell division | To produce RNA (mRNA, tRNA, rRNA, etc.) from specific genes | DNA replication is a preparatory step for mitosis/meiosis, while transcription supports protein synthesis. |
| Enzyme Involved | DNA polymerases | RNA polymerase | DNA polymerase requires a primer; RNA polymerase can initiate de novo. |
| Template | Double-stranded DNA | One strand of DNA (template strand) | Both use DNA as a template, but replication copies both strands; transcription uses one. |
| Product | Identical double-stranded DNA molecules | Single-stranded RNA (mRNA, tRNA, rRNA, etc.) | DNA synthesis maintains genome; RNA synthesis generates functional intermediates. |
| Direction of Synthesis | 5′ to 3′ on the new strand; DNA polymerase reads 3′ to 5′ on template | 5′ to 3′ on RNA; RNA polymerase reads DNA template 3′ to 5′ | Directionality is the same for both, with respect to the new strand. |
| Initiation Site | Origins of replication (ori) | Promoter regions upstream of genes | DNA replication starts at specific sequences; transcription begins at gene-specific regulatory elements. |
| Primer Requirement | Requires RNA primer to initiate synthesis | Does not require primer | RNA polymerase can begin synthesis without a free 3′-OH group. |
| Extent of Synthesis | Entire genome is replicated | Only specific genes or regions are transcribed | DNA replication is comprehensive; transcription is selective. |
| Termination Mechanism | Termination sequences or structures (e.g., ter sites, replication fork collapse) | Termination signals in DNA or RNA structure | Both have well-defined termination mechanisms, but via different elements. |
| Fidelity/Error Rate | Very high fidelity due to proofreading by DNA polymerases | Lower fidelity; limited proofreading by RNA polymerase | DNA polymerases have 3′→5′ exonuclease activity; RNA polymerase lacks robust proofreading. |
| Proofreading Capability | Present (especially in DNA polymerase III, I in prokaryotes) | Minimal proofreading (some correction in RNA Pol II) | Important to ensure genetic stability in DNA; RNA errors are often tolerated. |
| Base Pairing Rules | A–T, G–C | A–U, G–C (uracil replaces thymine) | RNA contains uracil instead of thymine. |
| Nucleotides Used | dATP, dGTP, dCTP, dTTP | ATP, GTP, CTP, UTP | DNA uses deoxyribonucleotides; RNA uses ribonucleotides. |
| Cell Cycle Phase | Occurs during S phase (eukaryotic cells) | Can occur throughout interphase (G1, S, G2) | DNA replication is tightly regulated; transcription is continuous based on gene activity. |
| Location | Nucleus (eukaryotes); cytoplasm (prokaryotes) | Nucleus for transcription; cytoplasm for further RNA processing (eukaryotes) | Both processes occur in the cytoplasm in prokaryotes; in eukaryotes, transcription is compartmentalized. |
| Energy Requirement | Requires energy from nucleotide hydrolysis and helicase activity | Requires NTP hydrolysis during elongation | Both are energy-dependent processes. |
| Associated Proteins | DNA polymerases, helicase, ligase, topoisomerase, primase, SSB proteins | RNA polymerase, general transcription factors, enhancers, silencers | DNA replication is more complex structurally; transcription has more regulatory proteins. |
| Strand Usage | Both strands are templates (leading and lagging strands) | Only one strand of DNA is used as a template | Transcription produces a complementary RNA from a single DNA strand. |
| Resulting Function | Genetic material duplication for daughter cells | Gene expression and regulation | DNA replication ensures heredity; transcription enables function. |
| Cellular Outcome | Two identical DNA molecules; each daughter cell receives one | mRNA used in translation; tRNA and rRNA function in protein synthesis | Replication is preparative; transcription is functional. |
| Experimental Applications | PCR, DNA sequencing, cloning, forensic analysis | RT-PCR, transcriptomics, gene expression profiling | Both are fundamental to molecular biology and biotechnology. |
