Practice Quiz

IB Biology Exam Prep

Category - Biology

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Which of the following best describes an operator in prokaryotic gene expression?
  1. It is a specific nucleotide sequence that indicates where DNA replication begins.
  2. It controls access of RNA polymerase to the genes in a transcription unit.
  3. It is a transposable genetic element that activates an operon.
  4. It controls access of RNA polymerase to the genes in a transcription unit.
  5. None of the above
Explanation
Correct Response: D. An operator is a DNA sequence to which a repressor can bind, blocking RNA polymerase from transcribing prokaryotic genes. The operator does not function as an origin of replication (A), nor is an operator able to remove introns, which are non-coding sections of RNA (B). A spliceosome typically performs this process. Transposable elements are DNA segments capable of excising and reinserting themselves into new locations within the chromosome (C). They do not activate operons.
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