Definition

Noun: A type of enzyme (nuclease) that cleaves nucleotides one at a time from the end of a DNA or RNA molecule. It works sequentially, beginning at either the 3' or 5' terminus of the nucleic acid chain.

Usage

The term is used in molecular biology and genetics to describe enzymes that degrade nucleic acids from the ends, in contrast to endonucleases which cut internally. - It is a countable noun (e.g., an exonuclease, several exonucleases). - It is often specified by the direction of its activity (e.g., 3'→5' exonuclease, 5'→3' exonuclease).

Examples

• In a general statement:
  • DNA polymerase I has an exonuclease activity that proofreads newly synthesized DNA.
• Describing a specific function:
  • The researcher used an exonuclease to remove nucleotides from the 3' end of the RNA probe.
• In a comparative context:
  • Unlike an endonuclease, an exonuclease requires a free end to initiate digestion.

Advanced Usage

• Process/Activity: The term can refer to the enzymatic activity itself.
  • The exonuclease activity is crucial for DNA repair mechanisms.
• As a Modifier: Used adjectivally in compound terms (listed in variants).
  • The exonuclease domain of the enzyme is highly conserved.

Variants and Related Words

• Exonucleolytic (adjective): Pertaining to or characterized by exonuclease activity.
  • The exonucleolytic degradation was monitored over time.
• Exoribonuclease (noun): A specific type of exonuclease that acts on RNA.
• Exodeoxyribonuclease (noun): A specific type of exonuclease that acts on DNA.

Synonyms

• Terminal nuclease: A less common synonym emphasizing action at the terminus.
• Nuclease (specific type): While "nuclease" is the broader category, "exonuclease" specifies the mode of action.

Notes on Meaning

The core meaning is defined by its direction of cleavage (from an end) and its mechanism (sequential removal of single nucleotides). This distinguishes it fundamentally from endonucleases. Its primary role in biological systems is in processes like DNA replication proofreading, repair, and RNA turnover.

Noun

1. a nuclease that releases one nucleotide at a time (serially) beginning at one of a nucleic acid