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Explain why half of DNA is replicated in a discontinuous fashion. a. Replication of the lagging strand occurs in the direction away from the replication fork in short stretches of DNA, since access to the DNA is always from the 5’ end. This results in pieces of DNA being replicated in a discontinuous fashion. b. Replication of the leading strand occurs in the direction away from the replication fork in short stretches of DNA, since access to the DNA is always from the 5’ end. This results in pieces of DNA being replicated in a discontinuous fashion. c. Replication of the lagging strand occurs in the direction of the replication fork in short stretches of DNA, since access to the DNA is always from the 5’ end. This results in pieces of DNA being replicated in a discontinuous fashion. d. Replication of the lagging strand occurs in the direction away from the replication fork in short stretches of DNA, since access to the DNA is always from the 3’ end. This results in pieces of DNA being replicated in a discontinuous fashion.

Step by step solution

01

Understand DNA Replication

DNA replication involves unwinding the double helix and synthesizing new strands from each of the original strands. Each new strand is built in the 5’ to 3’ direction.

02

Leading and Lagging Strands

The leading strand is synthesized continuously in the direction of the replication fork (5' to 3'). The lagging strand, however, is synthesized in short stretches in the direction away from the replication fork.

03

Directionality Constraints

DNA polymerase can only add nucleotides to the 3' end of a primer. This means that replication on the lagging strand must happen in short, discontinuous segments known as Okazaki fragments, because the polymerase has to work away from the replication fork.

04

Identify the Correct Answer

Option a. correctly states that replication of the lagging strand occurs in the direction away from the replication fork in short stretches of DNA, since access to the DNA is always from the 5’ end. This results in DNA being replicated discontinuously.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

lagging strand

In the process of DNA replication, the lagging strand is synthesized discontinuously. This is because DNA polymerase can only add new nucleotides in a 5’ to 3’ direction. The replication fork unwinds the DNA, separating the strands. The lagging strand must elongate away from the replication fork. Therefore, it is built in short segments called Okazaki fragments. These fragments are later connected by the enzyme DNA ligase to create a continuous strand.

Here are key points to remember about the lagging strand:

• It is synthesized discontinuously in short sections known as Okazaki fragments.
• The replication process moves away from the replication fork.
• DNA ligase is needed to join the Okazaki fragments together.
• It replicates in a 5' to 3' direction, but opposite to the unwinding direction of the fork.

leading strand

Unlike the lagging strand, the leading strand is synthesized continuously during DNA replication. It grows in the same direction as the replication fork, which allows it to be made in one continuous piece. This continuous synthesis makes it much simpler compared to the lagging strand, which is built in fragments.

Some important details about the leading strand include:

• It is synthesized in a continuous manner.
• The direction of synthesis is the same as the movement of the replication fork.
• Like the lagging strand, it also extends in a 5’ to 3’ direction.

Since the template strand for the leading strand runs in a 3' to 5' direction, DNA polymerase can function smoothly without interruptions.

Okazaki fragments

Okazaki fragments are short sequences of DNA nucleotides which are synthesized discontinuously. They occur on the lagging strand during DNA replication. These fragments are essential because DNA polymerase can only synthesize new DNA in a 5’ to 3’ direction. During replication:

• The lagging strand template, which reads from 3’ to 5’, necessitates the creation of these fragments.
• RNA primers provide starting points for DNA polymerase to begin synthesis of each fragment.
• Once multiple Okazaki fragments are synthesized, they are joined together by DNA ligase to form a continuous strand.

By filling in the gaps between individual fragments, the replication machinery ensures that the lagging strand is accurately copied and completed in a fragmented yet effective manner.