Which type of enzyme is classified as an endonuclease?

An endonuclease is an enzyme that plays a crucial role in molecular biology by cleaving the phosphodiester bonds within a nucleic acid strand. This action allows the enzyme to cut the nucleic acid at specific internal sites, rather than just at the ends.

The classification of endonucleases is based on their ability to function within the nucleotide sequence, making them essential in various biochemical processes, such as DNA replication, repair, and RNA processing. These enzymes are particularly useful in laboratory settings for manipulating DNA or RNA for cloning, sequencing, or other forms of genetic analysis.

The other options describe different types of enzymes that do not fit the definition of endonucleases. An enzyme that joins DNA fragments is known as a ligase, those that digest nucleic acids from the ends are termed exonucleases, and enzymes that synthesize RNA are known as RNA polymerases. Each of these enzymes has distinct functions and mechanisms that are fundamentally different from those of endonucleases.