Générateur de séquence DNA / RNA

GC content is the percentage of guanine (G) and cytosine (C) bases in a nucleic acid molecule. Because G–C pairs share three hydrogen bonds compared with two for A–T pairs, regions with higher GC content have a higher melting temperature and greater structural stability. GC content also varies systematically across organisms and genomic regions, so controlling it is important when designing primers, generating realistic synthetic data, or modeling specific taxa.

The complement of a strand replaces each base with its Watson–Crick partner (A↔T, G↔C, A↔U for RNA) while preserving the 5′ to 3′ reading direction. The reverse complement does the same base substitution and then reverses the string so that it represents the actual sequence of the antisense strand read 5′ to 3′. Reverse complement is what biologists usually want when pulling the opposing strand from a double-stranded molecule.

Transcription is the biological process of copying a DNA template into RNA, which mechanically corresponds to swapping each thymine (T) for uracil (U). Reverse transcription is the opposite — converting an RNA molecule back into complementary DNA (cDNA) by replacing each U with T. Real cells use enzymes (RNA polymerase and reverse transcriptase) for these conversions; the sequence-level transformation is a simple character swap.

The IUPAC nucleotide codes are single-letter symbols that represent positions where more than one base may occur. R stands for purine (A or G), Y for pyrimidine (C or T/U), S for strong (G or C), W for weak (A or T/U), K for keto (G or T/U), M for amino (A or C), and N for any base. They are commonly used in primer design, consensus motifs, and multiple sequence alignments where positions are degenerate or unknown.

FASTA is a plain-text format for representing nucleotide or protein sequences. Each entry begins with a single description line that starts with a greater-than symbol (>), followed by an identifier and optional metadata, and is then followed by one or more lines of sequence characters. Sequences are typically wrapped at 60 or 80 characters per line. FASTA is the lingua franca of bioinformatics tooling because it is human-readable and trivially parseable.