Question

1. ssdna stands for \single - stranded dna\ and dsdna for \double - stranded dna.\
2. the grayed - out insert, in the circle to the right, shows the split that forms the replication fork and how the single - stranded sections of the leading and lagging strands thread through the machine.
3. helicase, in blue and pictured at the far left here, is an enzyme that \unzips\ dna, breaking hydrogen bonds between complementary pairs to create ssdna.
4. the thioredoxin molecules shown in yellow help the complex move along the dna strands as replication continues.
5. an important enzyme called topoisomerase is not shown here but is sometimes considered part of the replisome. its function is to break and rejoin dna ahead of the replisome, to relieve the twisting force that is created as helicase continuously unzips the double helix. (you may have seen this twisting force in action if youve ever pulled the strands in a rope or braid apart on one end, and seen the other end jump or even kink on itself.)

if you look at the model carefully, you can see that the two copies of dna polymerase are in physical contact but are oriented at 180 degrees to each other—they face opposite ways. why? choose the single best answer.
they are each synthesizing dna 5 to 3, but work in the opposite direction because of the antiparallel orientation of the leading and lagging strands.
they are different versions of dna polymerase, with different structures and completely different functions, so they have different active sites and different orientations in the replisome.
one is involved in dna synthesis; the other is involved in keeping the leading and lagging strands separate and single - stranded.

Explanation:

DNA polymerase synthesizes DNA in the 5' to 3' direction. The two strands of DNA (leading and lagging) are antiparallel. So, to synthesize both strands simultaneously (as part of the replisome complex), the two copies of DNA polymerase must face opposite directions. DNA polymerase enzymes are not different in structure and function in this context (they all synthesize DNA), and the function of keeping strands separate is mainly of helicase (and single - strand binding proteins, not DNA polymerase).

Answer:

They are each synthesizing DNA 5' to 3', but work in the opposite direction because of the antiparallel orientation of the leading and lagging strands.