DNA replication copies a double-stranded DNA molecule into two daughter double-stranded DNA molecules. In semiconservative replication, each daughter retains one parental strand and receives one newly synthesized complementary strand. DNA polymerases build the new strands from incoming nucleotides; they do not make RNA or proteins in this copying step. See Alberts et al., Molecular Biology of the Cell, 4th edition (2002): DNA replication mechanisms.
For a five-base pair example, separate from its partner . Base pairing specifies a new TACGG partner for the old ATGCC strand and a new ATGCC partner for the old TACGG strand. With error-free copying, both daughter DNA molecules have the original nucleotide sequence, but different physical strand histories. One initial duplex contains ten nucleotides; one complete round produces two duplexes containing twenty nucleotides, ten retained and ten newly incorporated.
Semiconservative replication: follow two original DNA strands through two complete copying rounds
. Blue O1 and purple O2 are the original strands; green strands were made in round 1 and orange strands in round 2. Each arrow connects a parent duplex to its daughters. After round 2, two of four duplexes retain an original strand, and the other two retain a round-1 strand. All eight strands have the appropriate complementary nucleotide sequences; colors identify strand age, not different nucleobases. The flattened duplexes show ancestry and orientation, not a replication fork or molecular shape. Details.This is useful for inheritance: both daughter biological cells can receive a copy of the DNA record. The elegant feature is that base pairing lets each strand specify its missing partner. Direction matters too: a replicating DNA polymerase reads its template and extends the new strand at its end, so synthesis proceeds . These are opposite directions on antiparallel nucleic acid strands, not two alternative directions of synthesis. The enzyme needs a pre-existing paired strand end to extend; the diagram omits the machinery that starts and coordinates copying. See Alberts et al.: template-directed synthesis and the requirement for a primer.
The strand accounting predicts observable differences between copying mechanisms. In 1958, Meselson and Stahl grew Escherichia coli with the heavier nitrogen isotope , then supplied and measured extracted DNA by density-gradient centrifugation. After one generation their samples contained intermediate-density DNA; after two, intermediate-density and light DNA occurred in equal amounts. This supported semiconservative replication in the tested Escherichia coli culture. It was an isotope assay of sampled DNA, not simultaneous testing of every kind of DNA or direct colored-strand photography. See The replication of DNA in Escherichia coli by Matthew Meselson and Franklin W. Stahl.
A mismatch's Boltzmann weight relative to the correct pair depends on which base is the fixed template, not just on the unordered mismatch name. In a rigid two-versus-three-hydrogen-bond cartoon, replacing the incoming base with the same wrong pair can lose a different number of bonds for the opposite template orientation. Proofreading and nonequilibrium polymerase discrimination make such pair-energy weights insufficient as a complete replication-error model.
An inhibitor of replicative DNA polymerases used to impose replication stress. Increased fragility after treatment supports replication-sensitive vulnerability without identifying every molecular intermediate.
DNA whose copying has not completed at a relevant cell-cycle transition. It can contribute to abnormal mitotic structures or breakage, but requires evidence distinct from a general DNA-damage signal.
Use of an alternative template during synthesis or damage tolerance. Appropriate switching can bypass a block; inappropriate switching can alter sequence organization.
DNA synthesis across a lesion by an appropriate polymerase. It can allow replication to continue without removing the original lesion, and its accuracy is substrate dependent.
Misalignment of nascent and template strands during copying, especially at repeats. A retained nascent-strand loop can yield insertion, whereas a looped-out template can yield deletion.
Removal of a misincorporated terminal nucleotide by a suitable proofreading exonuclease, commonly acting in the 3′→5′ direction. It is distinct from later DNA mismatch repair.
Impaired progression or completion of DNA replication. Stalled or damaged forks can lead to genome alterations if not appropriately stabilized, restarted or repaired.
A loss of register between template and growing strand during copying, especially in repetitive sequences. It can generate indels in cells or stutter artifacts during experimental amplification.
Replication licensing prepares DNA replication origins for a subsequent initiation event. Separation of licensing from initiation and inhibition of relicensing during high-CDK phases helps prevent repeated copying within one cell cycle.
The daughter strand synthesised through repeated priming and joining of fragments because DNA polymerases extend only in one chemical direction.
The daughter strand synthesised predominantly in the direction of overall fork movement in conventional replication.
The moving region where parental DNA is unwound and daughter strands are synthesised. Its speed is distinct from the duration of whole-genome replication.
A fork that has lost the integrity or organization needed for ordinary progression, potentially including a DNA break. Restoration requires more than correction of a base mismatch.
The E. coli replication-fork barrier involving Tus protein and Ter DNA sites, a specific bacterial termination arrangement rather than a universal bacterial mechanism.
A topological interlink between DNA molecules, including replicated duplexes that must be resolved for successful segregation.
The difficulty conventional replication machinery encounters in completely copying the ends of linear DNA molecules after terminal primer removal.
A short RNA segment providing a paired 3-prime end from which DNA synthesis can be extended. It is subsequently removed or processed during strand maturation.
A short DNA segment initiated on the lagging strand and later joined with neighbouring segments to produce a continuous daughter strand.
Replication factor C, a clamp-loading complex involved in installing PCNA on suitable DNA structures.
Proliferating cell nuclear antigen, the eukaryotic sliding clamp that supports DNA synthesis and coordinates associated processes.
The ring-shaped bacterial processivity factor that helps maintain association between DNA polymerase and its template.
Inappropriate recopying of already replicated nuclear DNA within a cell-cycle interval, prevented by controls separating origin licensing from firing.
A component of the active eukaryotic CMG replicative helicase.
The active eukaryotic replicative helicase assembled from Cdc45, MCM2-7 and GINS, translocating on the leading-strand template.
A bacterial replication initiator that acts at the E. coli origin, oriC, with regulation involving nucleotide state and cellular conditions.
A heterohexameric complex forming the motor core of the eukaryotic replicative helicase. Inactive double hexamers are loaded during licensing before conversion into active CMG helicase complexes.
A licensing factor cooperating with the origin recognition complex and Cdt1 to load the MCM2-7 replication-helicase precursor.
A protein complex that participates in recruitment of factors for replication origin licensing in eukaryotes.
Loading of an inactive replication-helicase precursor that makes an origin competent to fire later. In conventional eukaryotic cycles, low kinase activity permits licensing and subsequent high kinase activity promotes firing while preventing renewed licensing.
Control separating competence to initiate from actual origin firing so that genomic regions are not repeatedly copied within one S phase. Details include kinase activity and organism-specific licensing inhibitors.
An ATP-dependent protein complex that installs a sliding clamp at an appropriate DNA structure, enabling processive synthesis and associated functions.
In semiconservative replication, each daughter duplex retains one strand of its immediate parent. Under complete copying without strand loss or exchange, one starting duplex gives duplexes after rounds, but still only two original strands. For , the fraction of duplexes containing an original strand is : all after one round, half after two, a quarter after three. The fraction of all strands that are original is instead . A strand made in round 1 is parental when round 2 begins.
A replicating DNA polymerase is an enzyme that extends a paired strand end with nucleotides selected against a DNA template. New DNA grows while the template is read . Base pairing specifies the partner; the DNA polymerase catalyzes its incorporation. See Alberts et al.: DNA polymerase.
An E. coli polymerase participating in primer removal and gap filling, distinct from the principal chromosomal replicase DNA polymerase III.
A eukaryotic replicative polymerase with a predominant lagging-strand role, also participating in initiation, strand displacement and repair contexts.
A eukaryotic replicative polymerase with a predominant leading-strand role during conventional nuclear replication.
The eukaryotic initiation complex that synthesises an RNA primer and then a short DNA extension before handoff to more processive polymerases.
The principal E. coli chromosomal replicative DNA polymerase, operating with a sliding clamp and associated replication factors.
Taq polymerase is a heat-resistant DNA polymerase used in PCR amplification. It requires a paired strand end and nucleotide substrates; heat resistance does not confer target recognition.
A deoxynucleoside triphosphate is a nucleotide containing deoxyribose and three phosphate groups. DNA polymerases use these substrates to extend DNA; the four standard substrate types carry adenine, cytosine, guanine or thymine.
A DNA replication inhibitor interferes with DNA replication; the observed effect depends on exposure and assay conditions.
A replicon is a DNA unit replicated from an origin of replication. A plasmid can form a replicon separate from a host chromosome.
An origin of replication is a DNA region at which DNA replication is initiated. Its function depends on compatible cellular machinery.
The chromosomal origin of replication in E. coli, where DnaA-dependent initiation assembles bidirectional replication machinery.
Articles by others on the same topic
DNA replication is the biological process through which a cell makes an exact copy of its DNA. This process is essential for cell division and is crucial for inheritance, growth, and repair in living organisms. Here’s a brief overview of how DNA replication occurs: 1. **Unwinding**: The double helix structure of the DNA is unwound by enzymes called helicases. This creates two single strands of DNA, which serve as templates for replication.
