1. What is Plasmid Copy Number?

The plasmid copy number (CN) represents the number of copies of a plasmid present in a single bacterial cell relative to the single copy of the genomic DNA. It's an important parameter in molecular biology and genetic engineering.

2. How Does the Calculator Work?

The calculator uses the following equation:

Where:

• \( Ct_g \) — Threshold cycle for genomic DNA
• \( Ct_p \) — Threshold cycle for plasmid DNA

Explanation: The equation calculates the relative copy number based on the difference in threshold cycles (Ct values) between genomic and plasmid DNA in qPCR experiments.

3. Importance of Copy Number Calculation

Details: Knowing plasmid copy number is essential for gene expression studies, protein production optimization, and maintaining plasmid stability in bacterial cultures.

4. Using the Calculator

Tips: Enter the Ct values obtained from qPCR experiments for both genomic DNA and plasmid DNA. The values should be from the same sample run under identical conditions.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical plasmid copy number?
A: Copy numbers vary widely depending on plasmid origin of replication, from 1-2 copies per cell (low-copy) to 500+ copies per cell (high-copy).

Q2: Why use genomic DNA as reference?
A: Genomic DNA serves as a single-copy reference since each bacterial cell contains exactly one copy of its chromosome.

Q3: How accurate is this method?
A: The method provides a good estimate but assumes 100% PCR efficiency. For more precise measurements, standard curves should be used.

Q4: Can I use this for eukaryotic cells?
A: The principle is similar, but you would need to adjust for ploidy and chromosome copy number in eukaryotic systems.

Q5: What if my Ct values are very close?
A: If Ct_g ≈ Ct_p, the copy number is approximately 1 (single copy). Small differences in Ct values can lead to large differences in calculated copy numbers.