AP BIOLOGY

Detailed explanation-1: -RecBCD binds to the ends of a double stranded DNA break and initiates unwinding of the duplex using its ATP-dependent helicase activity. RecBCD also contains a single stranded (ss)DNA exonuclease activity that initially degrades the unwound ssDNA from both the 3’ and 5’ ends.

Detailed explanation-2: -Helicases are enzymes that use ATP-driven motor force to unwind double-stranded DNA or RNA.

Detailed explanation-3: -History of DNA helicases DNA helicases were discovered in E. coli in 1976. This helicase was described as a “DNA unwinding enzyme” that is “found to denature DNA duplexes in an ATP-dependent reaction, without detectably degrading".

Detailed explanation-4: -During replication, the helicase has to unwind a long stretch of DNA, and that requires the helicase to couple strand-separation activity to translocation. The mechanisms of these critical processes of the helicase reaction are largely unknown.