Answer to Question #62777 in Molecular Biology for Sanjukta Ghosh

Question

I stumbled upon this paragraph in a book and couldn't make out what it means.

Link for the paragraph:http://biology.stackexchange.com/questions/52585/primase-activity-and-leading-strand

Doubts:

(1) What is meant by 'in the direction opposite to that in which the DnaB helicase is moving'? Does it mean that the DnaG will separate from the Helicase to move in opposite direction ( 5'−> 3') and synthesise a short RNA strand?

(2) I don't quite understand what is meant by opposite direction in the second quotation.

P.S. I couldn't couldn't accommodate the paragraph due to word limit so provided an external link.

Answer 1

Synthesis of DNA can occur only in one direction, and it always occurs in this direction. And there was intriguing question in the beginning of DNA synthesis studying - how can it be if helicase moves only in one direction and strands are antiparallel? It turned out that the only the first DNA strand is synthesized continuously (the leading strand), and the second strand had to be synthesized discontinuously, fragment by fragment (ladding strand). These fragments, also called as Okazaki fragments, are synthesized in the direction opposite to the helicase moving.