Question

If the fragment of DNA shown below were to replicate, on which strand (A or B) would Okazaki fragments be formed? The origin of replication is at the right and the replication fork proceeds towards the left. Explain your reasoning.

Strand A: 5 -ATCGATCCCTAG-3
Strand B: 3 -TAGCTAGGGATC-5

Answer 1

thats the answer i was reading yet there is another answer if found on yahoo as well. Not sure which is the correct one.

They would form on strand B.

Explanation:
DNA is always synthesized in a 5' to 3' direction and a DNA helix is always antiparallel (the two strands that base-pair to make the helix are oriented in the opposite direction as drawn in your example). For this reason, as the replication fork is proceeding to the left, Strand A is replicated continuously because it is oriented in the opposite direction of the synthesized strand. To put it in other words, if the orientation of a strand is 3' to 5', the complementary DNA will be synthesized in a 5' to 3' direction.

Strand A: 5 -ATCGATCCCTAG-3 (DNA will be make in the following manner:)
<---------------------------- 3-GATC-5

Strand B on the other hand is oriented in a 5' to 3' manner. DNA cannot be replicated in a continuous manner since replication fork is moving to the left which means that strand B would have to be synthesized in a 3' to 5' manner; this is not how DNA is synthesized.
This is NOT how DNA is replicated:
<---------------------------- 5-CTAG-3
Strand B: 3 -TAGCTAGGGATC-5

So, strand B has to be synthesized as okazaki fragments:
.....................5-CG--> 5-CTA-->
Strand B: 3 -TAGCTAGGGATC-5

Answer 2

yeah could work.....

Answer 3

so would it be A or b?

Answer 4

and then found this

Despite this being biology, I'll still answer it.

This is the structure of a nucleotide. Notice that ONLY the 3' end is free for the molecule to be extended.

As such, DNA Polymerase III can ONLY add to the 3' end of a strand of DNA - this means that on one strand it will add continuously, whilst on the other strand it will add in short sections (okazaki fragments) as the DNA is denatured.

For the ones you posted, the okazaki fragments will form on Strand A.

Answer 5

\(\Huge\color{maroon}{\text{Genius :)}}\)

Answer 6

so would it be strand A or B is correct?

Answer 7

It is the strand B. The first explanation you provided illustrate it very well. Check out the following post whereby I mentioned the Okazaki fragments:
http://openstudy.com/study#/updates/53151d99e4b09b97a1862c86

Answer 8

replication happens from the 5' to 3' direction of the new strand being formed and DNA is antiparallel. Therefore the complimentary strand to strand A is being formed away from the replication fork (this is the lagging strand) and the complimentary strand to strand B is being towards the replication fork (this is the leading strand). The leading strand can form continuously but the lagging strand is formed in small fragments, each beginning with an RNA primer since DNA polymerase cannot initiate a new fragment without a free 3' end. When the primers are removed, you are left with small fragments of DNA with spaces in between. these are the okazaki fragments. Therefore, since strand A is the lagging strand, this is where the okazaki fragments will be found.

Other answer I found, thats why I'm confused which strand is right.