How to Make Billions of Copies of a DNA Segment

This patent describes the Polymerase Chain Reaction (PCR), a method to rapidly create many copies of a specific piece of DNA or RNA, enabling its detection and analysis.

What it covers

This patent details a process for amplifying and detecting specific nucleic acid sequences. First, a sample containing DNA or RNA is treated with two short DNA pieces called oligonucleotide primers, one for each strand of the target sequence (Claim 1a). These primers attach to the target, and an enzyme then extends them, building new complementary strands. Next, the sample is heated to separate the newly made strands from their original templates (denaturing, Claim 1b). The process of adding primers and extending them is then repeated, using the newly separated strands as templates (Claim 1c). Repeating these steps many times creates a massive number of copies of the target sequence (Claim 2). Finally, a labeled probe is added to detect if the amplified sequence is present (Claim 1d, 1e). For example, this process can detect a specific genetic mutation like the one causing sickle cell anemia (Claim 11, 12).

What it doesn't cover

• —Does not cover amplification methods that do not use two oligonucleotide primers for each strand of the target sequence.
• —Does not cover detection methods that do not involve adding a labeled oligonucleotide probe after amplification.
• —Does not cover processes where the primer extension products are not separated from their templates before further amplification steps.
• —Does not cover amplification using enzymes that are inactivated by the high temperatures required for strand separation, unless a heat-stable enzyme is explicitly used (Claim 15).
• —Does not cover methods that amplify nucleic acids without repeating the primer extension and denaturation steps at least once.

The clever bit

The core innovation was the realization that by repeatedly heating DNA to separate its strands and then cooling it to allow primers and an enzyme to build new copies, a specific DNA segment could be exponentially amplified. This cycling process, especially with a heat-stable enzyme (hinted at in Claim 15), made PCR incredibly efficient and practical.

Why it matters

This patent describes the Polymerase Chain Reaction (PCR), a foundational technique in molecular biology. It revolutionized genetic research, medical diagnostics, and forensic science by making it possible to study tiny amounts of DNA. The inventor, Kary Mullis, received the Nobel Prize in Chemistry for his work on PCR, highlighting its immense scientific impact. Cetus Corp, the original assignee, commercialized this technology, which became essential for countless applications.

Real-world examples

• 1.COVID-19 diagnostic tests (RT-PCR)
• 2.Forensic DNA analysis (e.g., crime scene investigation)
• 3.Paternity testing
• 4.Genetic disease screening (e.g., cystic fibrosis, sickle cell anemia)
• 5.Gene cloning and sequencing in research labs
• 6.Detection of pathogenic organisms in clinical samples