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BLASTN (Nucleotide), BLASTP (Protein), BLASTX (Translate Query), TBLASTN (Translate DB)
Picture This (Mental Hook): A bioinformatician sits at NCBI: blastn is for plain DNA vs DNA. blastp is for amino acids vs amino acids. When you don't know the reading frame, blastx translates your Query in 6 frames, while tblastn translates the entire Database!
📊 Visual Diagram & Mental Flow:
┌───────────┬─────────────────────┬──────────────────────────┬─────────────────────────────┐ │ Program │ Query Input │ Target Database │ Translational Operation │ ├───────────┼─────────────────────┼──────────────────────────┼─────────────────────────────┤ │ blastn │ Nucleotide (DNA/RNA)│ Nucleotide │ None (direct base matching) │ │ blastp │ Protein (Peptide) │ Protein │ None (scoring matrices PAM) │ │ blastx │ Nucleotide │ Protein │ Translates QUERY in 6 frames│ │ tblastn │ Protein │ Nucleotide │ Translates DB in 6 frames │ │ tblastx │ Nucleotide │ Nucleotide │ Translates BOTH in 6 frames │ └───────────┴─────────────────────┴──────────────────────────┴─────────────────────────────┘
🔍 The Decoded Sequence:
blastn
N to N
Compares nucleotide query against nucleotide database
blastp
P to P
Compares amino acid query against protein database using BLOSUM62
blastx
Trans Query
Translates nucleotide query into 6 reading frames to find protein hits
tblastn
Trans DB
Compares protein query against 6-frame translated nucleotide database
Examiner Trap / Never Forget: BLOSUM matrices (e.g. BLOSUM62) are derived from observed local alignments in blocks of closely related proteins. Higher BLOSUM numbers (BLOSUM80) are for closely related sequences, lower numbers (BLOSUM45) for distant homologues!
