MOL - Replication [LESSON]

Replication

DNA replication occurs during the synthesis (S) phase of interphase. The cell has been signaled that it is going to divide and the next logical step is to create a copy of ALL of the DNA in the cell. Prokaryotes need to simply copy their one circular chromosome, but eukaryotes need to copy multiple linear chromosomes. The goal of replication is to make an exact copy of the DNA so that the new cell will have the recipe book for creating any proteins it may need.

The basic idea is that the strands are opened by enzymes, each side is copied in a specific direction, and then we have two identical copies as shown below.

DNA double helix
Hydrogen bonds break and helix opens

However, the process carried out in the cell looks much more like the image below – it is extremely complex. 

The image shows all of the enzymes involved in replication and their location during the process.

Watch the Replication video below to learn more. This is a very complex process, so you may need to stop and rewind a couple of times.

Now, sequence the events below to represent the correct order of DNA replication in the Replication Sequence Ordering learning activity.

The leading and lagging strands can be very tricky to understand. Remember that each is in reference to the way that helicase is running. One strand could be the lagging strand in reference to one helicase and the leading strand in reference to another since there are two helicases running out from each of the multiple replication forks. Use the practice below to ensure that you understand how to code the complementary strand, how to label each end, and how to tell which one is leading and which one is lagging.

Which way is the new strand of DNA synthesized?

The new strand is ALWAYS synthesized in the 5’ right pointing arrow 3’ direction

Use the Replication Strand activity below to better understand the replication strands. Hover over each question mark to see what the replication would be, click answer to reveal all of the strands replication.

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