Question

Why can't both strands of DNA be replicated at the same time?

Answer 1

Answer: DNA is a molecule made up of two strands, twisted around each other in a double helix shape. The two strands are complementary which have a 5 prime end and a 3 prime end. To understand this question you must first understand the steps that follow.

DNA Replication:

Step one:

DNA Helicase (unzips) separates the strands.

Step two:

DNA Primase starts the process and makes a small piece of RNA called a primer. This marks the starting point for the DNA.

Step three:

DNA Polymerase binds to the primer and will make the new strand of DNA. DNA Polymerase can only add DNA bases in one direction, from the 5 prime end to the 3 prime end.

• The leading strand is made continuously.
• The lagging strand does not run continuously because it runs in the opposite direction. Each fragment is started with an RNA primer. DNA Polymerase then adds a short row of DNA bases from the 5 prime to 3 prime direction. This results in okazaki fragments because it can only replicate in small chunks. The process is repeated.

Step four:

Once the new DNA is complete the enzyme exonuclease removes all the RNA primers from both strands of DNA.

Step five:

Another DNA Polymerase fills in the gaps that are left behind with DNA.

Step six:

DNA Ligase seals up the fragments in DNA, in both strands to make a continuous double strand.

Final answer:

DNA Replication cannot replicate at the same time due to the leading and lagging strand.

Good luck!