Cloning Calculators

0 calculators tagged with “Cloning”

Molecular cloning is the process of inserting a DNA fragment of interest into a vector (plasmid, phage, or BAC) and propagating it in a host organism (usually E. coli) to produce multiple identical copies. The classical approach uses restriction enzymes to cut the insert and vector at compatible sites, DNA ligase to join them, and transformation to introduce the recombinant plasmid into bacterial cells. Modern cloning methods include Gibson Assembly, Gateway cloning, Golden Gate, and TOPO cloning — which avoid the need for compatible restriction sites. Cloning underlies recombinant protein production, transgenic organisms, gene therapy, and functional genomics.

All Calculators

No calculators found for this topic.

Classical Restriction-Ligation Cloning

  1. Digest insert DNA and vector with compatible restriction enzymes → produce compatible sticky ends
  2. Gel-purify insert and linearized vector (remove uncut DNA)
  3. Ligate: T4 DNA ligase + ATP; 16°C overnight or room temperature for rapid ligation
  4. Transform: heat shock or electroporation into chemically competent or electrocompetent E. coli
  5. Select: plate on LB + antibiotic (ampicillin, kanamycin) + X-gal/IPTG for blue-white screening
  6. Screen: colony PCR, restriction digest, or Sanger sequencing of candidate clones

Modern Cloning Methods

  • Gibson Assembly: Overlapping PCR products + 5′ exonuclease + DNA polymerase + ligase → seamless assembly in one reaction; no restriction sites required
  • Gateway: Recombination-based; att sites flank insert; highly efficient; compatible with destination vector library
  • Golden Gate: Type IIS restriction enzymes cut outside their recognition sequence → precise overhangs; scarless multi-fragment assembly
  • TOPO cloning: Topoisomerase I covalently linked to blunt or A-tailed PCR products → simple one-step cloning

Cloning Vectors

pUC19: high-copy E. coli plasmid; ampicillin resistance; MCS; lacZ for blue-white screening. pET: T7 promoter-based expression vector. lentiviruses, AAV: mammalian expression; used in gene therapy.

Glossary

Molecular Cloning
Inserting a DNA fragment into a vector, transforming into E. coli, and propagating to produce many identical copies; classical method uses restriction enzymes, ligation, and antibiotic selection.
Gibson Assembly
Isothermal single-tube DNA assembly using 5′ exonuclease, polymerase, and ligase with overlapping PCR fragments; seamless; no restriction sites required; standard for multi-fragment assembly.
Selectable Marker
An antibiotic resistance gene (ampR, kanR) in a cloning vector; allows selection of transformed bacteria on antibiotic plates; only cells carrying the vector survive.

Frequently Asked Questions

Molecular cloning inserts a DNA fragment into a vector, then amplifies it in a host cell. Classical steps: (1) Choose restriction enzymes that cut both insert and vector at compatible sites; digest both with the same enzyme(s). (2) Gel-purify the insert fragment and linearized vector. (3) Ligate: T4 DNA ligase joins complementary sticky ends → recombinant plasmid. (4) Transform: introduce recombinant plasmid into E. coli (heat shock or electroporation). (5) Select: plate on antibiotic plates (only bacteria carrying the vector with antibiotic resistance gene grow). (6) Screen: colony PCR or mini-prep + restriction digest → identify clones with insert. (7) Verify: Sanger sequence the insert to confirm correct sequence and orientation.

Gibson Assembly (Daniel Gibson, 2009): a single-tube, isothermal method for assembling multiple overlapping DNA fragments. How it works: each fragment is PCR-amplified with 15–30 bp overlaps with adjacent fragments. Assembly mix contains: 5′→3′ exonuclease (chews back 5′ ends to reveal single-stranded 3′ overhangs); Phusion polymerase (fills gaps); Taq ligase (seals nicks). The exonuclease and polymerase activities combine to anneal overlapping ends → seamlessly join fragments. Advantages over restriction-ligation: no restriction sites required; seamless (no extra bases); can assemble 3–10+ fragments in one reaction; junctions can be designed precisely. Limitations: requires PCR to add overlaps; PCR errors may be introduced.

A cloning vector is a DNA molecule capable of self-replicating in a host cell that carries the inserted DNA. Essential features: Origin of replication (ori): allows autonomous replication in the host; determines copy number (pUC = high copy, ~500 copies/cell; pBR322 = low copy, ~20 copies). Selectable marker: antibiotic resistance gene (ampR, kanR, cmR) — allows selection of cells that received the vector; without it, most bacteria don't take up the plasmid. Multiple cloning site (MCS): cluster of unique restriction sites for inserting the fragment. Optional features: Reporter gene (lacZ for blue-white screening); promoter (for expression vectors like pET, pGEX); purification tags (His-tag, GST, MBP, FLAG); promoters compatible with mammalian cells (for expression in human cells).

After selecting colonies on antibiotic plates, verify that the correct insert was cloned: Blue-white screening: in pUC vectors with lacZ-MCS; insertion disrupts lacZ → white colony = insert present; blue = no insert (intact lacZ). Colony PCR: use primers flanking the MCS or insert-specific primers; amplify directly from colony; size-check on gel → correct band = insert present and approximately correct size. Restriction digest mini-prep: extract plasmid DNA; digest with enzyme(s) that cut within insert and vector; run gel → correct band pattern confirms insert size and orientation. Sanger sequencing: gold standard; sequence the insert to confirm correct sequence and orientation, check for PCR errors, verify reading frame for expression constructs.