Q.17 Accession number is a unique identification assigned to a

• (A) Single database entry for DNA/Protein
• (B) Single database entry for DNA only
• (C) Single database entry for Protein only
• (D) Multiple database entry for DNA/Protein

  Accession numbers serve as permanent, unique identifiers in bioinformatics databases like GenBank, UniProt, and EMBL. They enable precise retrieval of sequence records regardless of updates or versioning, forming the backbone of genomic data sharing.

  Correct Answer: (A) Single database entry for DNA/Protein
  Accession numbers identify individual database records containing either DNA or protein sequences (or both). Each submission gets a unique alphanumeric code (e.g., NM_000001, P12345) tracking that specific entry across versions.

  Accession Number Fundamentals

  When researchers submit sequences, databases assign stable accession numbers. DNA records (GenBank) use formats like “J00522” or “NM_001”; protein records (UniProt) use “P00533”. These persist even if sequences update—version numbers (e.g., NM_001.5) track changes while the accession remains constant.

  Explanation of All Options

  Each option’s accuracy regarding accession scope:

  • (A) Single database entry for DNA/Protein
    Correct. One accession = one record, applicable to nucleotide (GenBank/EMBL/DDBJ) or protein (UniProtKB) databases.

  • (B) Single database entry for DNA only
    Incorrect. Excludes protein databases like UniProt, Swiss-Prot where accessions identify protein records.

  • (C) Single database entry for Protein only
    Incorrect. Ignores nucleotide databases (GenBank) using same accession concept for DNA/RNA.

  • (D) Multiple database entry for DNA/Protein
    Incorrect. Accessions are unique to single records; cross-references use separate IDs.

  Option	Scope	Covers DNA?	Covers Protein?	Correct?
  (A) Single entry DNA/Protein	Both	Yes	Yes	✓
  (B) Single entry DNA only	Nucleotides	Yes	No	✗
  (C) Single entry Protein only	Proteins	No	Yes	✗
  (D) Multiple entries	Many records	N/A	N/A	✗

  Practical Bioinformatics Applications

  Example lookups:

  • DNA: NM_000546.6 → TP53 gene (NCBI)

  • Protein: P04637.6 → p53 protein (UniProt)

  Use accessions in BLAST searches, primer design, phylogenetic analysis. Essential for citing sequences reproducibly in publications and databases. For your biotech workflow: always record accession numbers when analyzing sequences!