The helicase modifies the DNA in such a way as to eliminate the affinity between the two strands.

Single-strand binding proteins bind the unwound DNA and prevent the double helix from re-forming.

The helicase pushes the two strands so far apart that they have no chance of finding each other.

DNA polymerase follows the helicase so closely that there is no chance for the strands to come back together.

ligase

primase

relievase

helicase

topoisomerase

nuclease

DNA polymerase I

ligase

primase

DNA polymerase III

ribosomes

sucrases

proteases

RNA primer

messenger RNA

ligase, primase, DNA polymerase, helicase

helicase, primase, ligase, DNA polymerase

primase, helicase, DNA polymerase, ligase

helicase, DNA polymerase, primase, ligase

helicase, primase, DNA polymerase, ligase

DNA ligase

DNA polymerase

primase

helicase

topoisomerase

sugar group ... phosphate group

3′ end ... 3′ end

5′ end ... 5′ end

3′ end ... 5′ end

5′ end ... 3′ end

ATAGGT

TATCCA

TGGATA

UAUCCA

TGGAUA

only one of the two strands can be used as a template for replication, because DNA polymerase only works in one direction

they both run in the 3' to 5' direction

one strand is actually composed of RNA

the two strands are mirror images

one strand runs in the 5' to 3' direction, and the other runs in the 3' to 5' direction