Question

Broken DNA can be repaired by DNA ligase (single-strand breaks) or nonhomologous end-joining (double-strand breaks). Explain why the cell’s set of repair enzymes also includes tyrosyl–DNA phosphodiesterases.

Short answer

In order for other enzymes to repair the DNA strand, it degrades the phosphotyrosyl from imprisoned topoisomerase, allowing its dissociation from DNA.

Step-by-step solution

DNA ligase

By facilitating the creation of a phosphodiester bond, the enzyme known as DNA ligase makes it easier to link DNA strands together.Although certain forms may only mend double-strand breaks, it contributes to the repair of single-strand breaks in duplex DNA in living things.

Cell’s set of repair enzymes includes tyrosyl–DNA phosphodiesterases

Topoisomerases cleave one or both DNA strands, covalently binding the 3’ or 5’ phosphate to a Tyr residue in the enzyme. It helps in maintaining the appropriate supercoiling in DNA during replication. The enzyme will remain attached to DNA if the catalytic cycle is not complete, which interferes with the replication and repair of DNA.

Tyrosyl-DNA phosphodiesterases break down the phosphotyrosyl from trapped topoisomerase allowing its disassociation from DNA so that other enzymes can repair the DNA strand.