How to Make Many Copies of a DNA Piece with Heat

This patent describes the Polymerase Chain Reaction (PCR) method, a technique to make millions of copies of a specific DNA segment using a heat-resistant enzyme and repeated temperature changes.

What it covers

The patent describes the core steps of the Polymerase Chain Reaction (PCR). It involves taking a DNA sample and adding building blocks called nucleoside triphosphates, short starting pieces called oligonucleotide primers, and a special heat-resistant enzyme (a "thermostable enzyme"). First, the DNA strands are separated by heating the mixture (claim 1(d)). Then, the mixture is cooled so the primers can attach to their specific spots on the single DNA strands (claim 1(e)). Next, the enzyme builds new DNA strands starting from these primers (claim 1(f)). This cycle of heating, cooling, and building is repeated many times, creating a huge number of copies of the target DNA sequence. For example, a tiny blood sample from a crime scene can be amplified to get enough DNA for forensic analysis.

What it doesn't cover

• —Amplification methods that do not use a thermostable enzyme, as claim 1(b) specifically requires a "thermostable enzyme."
• —Processes that do not involve repeated cycles of heating to separate DNA strands and cooling for primer binding and extension, as described in claim 1(d), (e), and (f).
• —Methods that do not use two oligonucleotide primers for each specific sequence being amplified, as claim 1(a) specifies "two oligonucleotide primers."
• —Amplification of RNA directly without first converting it to DNA, as claim 1 primarily focuses on amplifying "DNA or a mixture of nucleic acids."

The clever bit

The key innovation was combining the known principles of DNA replication with a *thermostable* enzyme. This allowed the reaction mixture to be heated to separate DNA strands without destroying the enzyme, meaning fresh enzyme didn't need to be added in each cycle, making the process efficient and automatable.

Why it matters

This patent describes the fundamental process of Polymerase Chain Reaction (PCR), a technique that revolutionized molecular biology and biotechnology. It enabled scientists to quickly and efficiently make millions of copies of specific DNA sequences from tiny samples. This capability became essential for genetic research, disease diagnosis, forensic science, and paternity testing, making previously impossible analyses routine.

Real-world examples

• 1.COVID-19 diagnostic tests
• 2.Forensic DNA analysis (e.g., crime scene investigation)
• 3.Paternity testing
• 4.Genetic disease screening
• 5.Gene cloning
• 6.Archaeological DNA studies