AP BIOLOGY

Detailed explanation-1: -To unwind a long stretch of DNA, a helicase has to move unidirectionally along the DNA and couple translocation to local base pair separation. As the helicase moves along the DNA, it successively makes and breaks interactions with the DNA.

Detailed explanation-2: -During DNA replication, DNA helicases unwind DNA at positions called origins where synthesis will be initiated. DNA helicase continues to unwind the DNA forming a structure called the replication fork, which is named for the forked appearance of the two strands of DNA as they are unzipped apart.

Detailed explanation-3: -Helicases are involved in virtually all cellular processes that involve DNA and RNA. Their claim to fame, though, is unwinding DNA so it can be copied during cell division.

Detailed explanation-4: -Topoisomerase I reduces the torsional strain in DNA resulting from local unwinding for replication and transcription by forming a transient complex with DNA catalysing the cleavage, unwinding and relegation of DNA.

Detailed explanation-5: -DNA helicases catalyze the disruption of the hydrogen bonds that hold the two strands of double-stranded DNA together. This energy-requiring unwinding reaction results in the formation of the single-stranded DNA required as a template or reaction intermediate in DNA replication, repair and recombination.