DNA synthesis—the process of building DNA molecules from individual nucleotide building blocks—is fundamental to all life on earth and underpins modern biotechnology. While cells naturally synthesize DNA during replication, scientists have developed powerful methods to create custom DNA sequences in the laboratory, revolutionizing research and medicine.
The Process of DNA Synthesis in Nature (DNA Replication)
In living organisms, DNA synthesis occurs primarily through “template-dependent” processes that make copies of existing DNA molecules. During cell division, DNA polymerase enzymes read DNA strands as templates and assemble complementary new strands by linking nucleotides (A, C, G, and T) in precise sequences matching the template. DNA polymerases can achieve remarkable accuracy through their proofreading ability, correcting errors as synthesis proceeds. Furthermore, cells have auxiliary proofreading machinery that helps detect and correct any errors missed by the polymerase’s proofreading activity.
The process unfolds in several carefully regulated steps:
- Initiation – Helicase enzymes unwind the double helix at origins of replication, creating a replication fork; Primase creates short RNA primers to provide a starting point for elongation.
- Elongation – DNA polymerase extends the new strand by pairing nucleotides with their complements in the template strand. If DNA polymerase incorporates a base which does not match the template, it stalls elongation until it can remove the incorrect base, after which it proceeds with synthesis (Proofreading).
- Termination – DNA polymerase stops elongating and falls off of the DNA molecule; other intracellular machinery removes RNA primers and joins fragments into one continuous sequence as necessary.
This template-dependent synthesis ensures faithful copying of genetic information from parent to daughter cells.
Template-Dependent vs Template-Independent DNA Synthesis
Interestingly, nature also performs limited “template-independent” synthesis— i.e. creating new DNA sequences from scratch. In our immune system, as precursor cells develop into B and T cells, they deliberately create random DNA sequences at specific junction points between certain gene segments that code for antibodies and T-cell receptors. This “junctional diversity”, on top of the combinatorial diversity generated by VDJ Recombination, contributes to the vast antibody repertoire needed to recognize countless foreign molecules—a rare example of controlled randomness in biological DNA synthesis.
De Novo DNA Synthesis: Building Custom Sequences
Unlike template-dependent synthesis that copies existing DNA, de novo synthesis creates entirely new sequences from scratch according to researchers’ specifications. This capability transforms how scientists study genes, develop therapeutics, and engineer organisms.
Chemical DNA Synthesis: Oligonucleotides and Their Uses
Since the 1980s, phosphoramidite chemistry has dominated de novo DNA synthesis. This chemical method builds DNA chains by adding one nucleotide at a time through a four-step cycle: deprotection, coupling, capping, and oxidation. Each cycle takes several minutes and achieves approximately 99.5% efficiency, meaning some molecules fail to incorporate the intended nucleotide.
This accumulation of errors limits phosphoramidite synthesis to relatively short DNA sequences called oligonucleotides, typically 100-200 nucleotides long. The harsh chemicals involved also damage DNA during synthesis, further restricting length and introducing modifications that differ from natural DNA.
Applications of synthetic oligonucleotides span scientific research and biotechnology. Oligonucleotides serve as PCR primers, enabling copying of specific DNA sequences for study, probes for detecting specific sequences, and as reagents for editing genomes. Furthermore, synthetic oligonucleotides can be stitched together into longer sequences such as complete genes or even genomes.
Gene Synthesis Through Oligonucleotide Assembly
To create longer DNA sequences than a few hundred bases, scientists must assemble multiple short oligonucleotides. Many vendors now offer this service, routinely serving scientists around the world with synthetic DNA molecules thousands of bases long for wide-ranging applications.
Polymerase cycling assembly (PCA) and similar techniques stitch together overlapping oligonucleotides, but each assembly step has the potential to introduce errors and failures. “Complex” sequences containing repeats, unusual structures, or extreme GC content often fail entirely with these methods.
Synthetic genes enable protein production, metabolic engineering, and basic research into gene function. However, length limitations and complexity restrictions have constrained what scientists can achieve.
Enzymatic DNA Synthesis: The Next Generation
Enzymatic DNA synthesis represents a paradigm shift, using modified enzymes rather than harsh chemistry to build DNA from scratch. These methods can achieve higher accuracy (>99.9% per cycle) and avoid damaging the growing DNA strands as occurs in chemical synthesis, enabling synthesis of much longer sequences directly.
Terminal deoxynucleotidyl transferase (TdT), the enzyme that naturally adds random nucleotides during antibody gene rearrangement, has been engineered for controlled synthesis. Companies including ours have developed TdT-based systems where the enzyme is reversibly blocked after adding each specified nucleotide, enabling a precisely controlled stepwise synthesis of a specified sequence with high efficiency.
Why Enzymatic DNA Synthesis Is More Accurate and Sustainable
The superior accuracy of enzymatic synthesis compounds dramatically over long sequences. While chemical synthesis might yield only 20% full-length product for a 300-nucleotide sequence, enzymatic methods can achieve over 75% full-length product—a seven-fold improvement. This enables direct synthesis of useful sequences up to 750 nucleotides, far exceeding chemical synthesis limits.
Longer oligonucleotides transform gene assembly. Building a 5,000-base gene requires over 40 chemically synthesized oligonucleotides but only 7-9 enzymatically synthesized ones, dramatically improving assembly success rates and reducing errors. Complex sequences that fail with chemical synthesis—including repeats, secondary structures, and extreme GC content—become accessible with enzymatic methods.
Environmental benefits also distinguish enzymatic synthesis. Aqueous reaction conditions replace toxic organic solvents, reducing hazardous waste and improving sustainability.
In short, chemical and enzymatic synthesis differences are striking: chemical DNA synthesis remains useful for short fragments, but it struggles with accuracy, length, and complex sequences. Enzymatic DNA synthesis overcomes these barriers—delivering longer, more precise, and more sustainable DNA production.
Current Applications of DNA Synthesis
Today, DNA synthesis already powers many essential tools in biology:
- Molecular biology: Supports gene cloning, mutagenesis, and the construction of plasmids and vectors.
- Genome editing: Provides CRISPR guide RNAs and DNA templates for homology-directed repair, which enables precise modifications to the genome of living cells.
- Diagnostics: Supplies synthetic DNA probes and standards for PCR, FISH, and sequencing validation.
- Drug discovery: Accelerates research through DNA libraries and enables recombinant protein production.
- Gene therapy: Enables construction of recombinant viral vectors that can deliver precise genetic payloads to cells.
- Cell therapy: Enables expression of recombinant proteins including chimeric antigen receptors to create “reprogrammed” living medicines .
- mRNA vaccines: Provides DNA templates for production of mRNA.
- Agricultural biotechnology: Provides DNA constructs that encode traits for crop improvement.
- Industrial biotechnology & metabolic engineering: Enables microbial strains with tailored genetic modifications or entire inserted metabolic pathways for sustainable chemical production.
Enzymatic DNA synthesis enables applications that were once out of reach, including:
- Greater access to much longer DNA constructs for complex genome editing
- A much wider range of regulatory elements for more precise control of cell and gene therapies for better efficacy and fewer side effects
- Longer templates with optimized untranslated regions for more potent and efficacious vaccines
- Large constructs that enable knock-ins of entire complex traits into crops
- Bioprospecting, refactoring, and reconstituting entire biosynthetic pathways for biomanufacturing starting from only metagenomic sequencing data
As synthesis technologies advance, scientists continue to expand the scale and precision of DNA design, creating new opportunities across healthcare, agriculture, and industry.
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Ansa Biotechnologies: Advancing Gene Synthesis Beyond Limits
Ansa Biotechnologies has commercialized enzymatic DNA synthesis technology capable of producing 750-nucleotide oligonucleotides—the longest commercially available. Our platform uses these oligonucleotides to build genes up to 7.5 kb routinely, and up to 50 kb in our early access program. This represents a substantial improvement over conventional limits for routine gene synthesis.
Beyond length, Ansa’s technology handles sequences that were previously impossible to manufacture using conventional scalable techniques. Our sequence-agnostic synthesis assembly methods work reliably regardless of complexity, and we use long-read sequencing to ensure that the material we create precisely matches the intended sequence. Our robust and scalable process enables us to guarantee delivery of complete orders on time—unprecedented in an industry plagued by delays and failures. This commitment serves as our DNA synthesis reliability guarantee, ensuring researchers can depend on every sequence they order. This makes Ansa’s platform one of the most advanced gene synthesis services available today.
What’s Next for DNA Synthesis
De novo DNA synthesis has progressed from chemical oligonucleotide synthesis to today’s enzymatic methods capable of producing long, complex sequences. These advances, which power our gene synthesis platform, remove historical constraints on DNA sequence space available for designs.
As synthesis technology continues to improve, the ability to write DNA as easily as we now read it will accelerate biotechnology’s impact on medicine, agriculture, chemicals, and materials.
The question shifts from “can we synthesize this DNA?” to “what DNA should we synthesize?”—limited only by our understanding of biological systems and our imaginations.