GC Content Calculator

GC content is the percentage of guanine (G) and cytosine (C) bases in a DNA or RNA sequence — a key measure used in genetics, PCR design, and genomic analysis to assess sequence stability and species identification. Paste your DNA/RNA sequence in plain text or FASTA format into the GC Content Calculator, then select your sequence type to get the GC Content %, nucleotide counts (A, T/U, G, C), sequence length, and estimated melting temperature (Tm). You can also set a window size for sliding window GC analysis across longer sequences.

Accepts A, T/U, G, C nucleotides. Non-standard bases are counted separately.

Optional: Analyze GC content in sliding windows of specified size

Results

GC Content

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Sequence Length

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Adenine (A)

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Thymine/Uracil (T/U)

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Guanine (G)

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Cytosine (C)

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Estimated Tm

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Results Table

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Frequently Asked Questions

What is GC content and why is it important?

GC content is the percentage of guanine (G) and cytosine (C) nucleotides in a DNA or RNA sequence. It's important because GC pairs are bound by three hydrogen bonds while AT pairs have only two, affecting DNA stability, melting temperature, and secondary structure formation.

How is GC content percentage calculated?

GC content is calculated as (Count of G + Count of C) / (Total count of A + T + G + C) × 100%. This gives you the percentage of the sequence that consists of guanine and cytosine bases.

Why does GC content matter in PCR experiments?

GC content affects the annealing temperature of primers and template DNA. Higher GC content increases melting temperature, requiring adjustment of PCR cycling conditions for optimal amplification efficiency and specificity.

What is a CpG island and how does it relate to GC content?

CpG islands are DNA regions with high GC content (>50%) and frequent CpG dinucleotides. They're often found in gene promoters and are important for gene regulation, especially in epigenetic modifications like DNA methylation.

How does GC content affect protein expression?

High GC content can lead to strong secondary structures in mRNA that may impede translation. In codon optimization for protein expression, GC content is balanced to ensure efficient translation while maintaining protein sequence.

What is the typical GC content range for different organisms?

GC content varies widely: human genome (~41%), E. coli (~50%), some bacteria can range from 25% to 75%. Extremophiles often have either very high or very low GC content adapted to their environments.

Can I analyze RNA sequences with this calculator?

Yes, this calculator works for both DNA and RNA sequences. For RNA, uracil (U) is treated equivalent to thymine (T) in the calculations, and the GC content principles remain the same.

What does the melting temperature (Tm) estimate represent?

The estimated Tm is the temperature at which 50% of DNA strands are denatured. It's calculated based on GC content using the formula: Tm ≈ 81.5°C + 16.6(log[Na+]) + 0.41(%GC) - 675/length. This is a rough estimate for short sequences.