Question

All of the following enzymes are involved in the replication process of DNA EXCEPT: (A) DNA helicase (B) DNA polymerase (C) RNA polymerase (D) RNA primase (E) DNA ligase

Short answer

The enzyme not involved in the DNA replication process is (C) RNA Polymerase.

Step-by-step solution

Understand the role of each enzyme

DNA Helicase is the enzyme that unwinds the double-stranded DNA. DNA Polymerase is the enzyme that synthesizes new strands of DNA. RNA Primase synthesizes a short RNA segment that serves as a primer for DNA polymerase. DNA Ligase is the enzyme that connects DNA fragments (Okazaki fragments on the lagging strand) together to create a single DNA strand.

Identify the enzyme not involved in DNA replication

RNA Polymerase is the enzyme that produces RNA by following a strand of DNA. This enzyme is not directly involved in DNA replication, but rather in transcription, which is the process of making RNA from a DNA template.

Key concepts

DNA helicase

DNA helicase plays a crucial role in the process of DNA replication by unwinding the double-stranded DNA. This enzyme is like a zipper, gliding along the DNA strand, causing it to separate into two single strands. This unwinding creates a replication fork, which is a structure that resembles a fork in a road, providing two paths for the new DNA to be synthesized.

Without DNA helicase, the DNA strands would remain tightly coiled, making it impossible for the replication process to occur. The action of separating the strands allows the other enzymes involved in DNA replication to access the DNA template. This ensures that each original strand can be copied by the other enzymes involved.

• Unwinds DNA strands
• Creates replication fork
• Enables access for other enzymes

DNA polymerase

DNA polymerase is the enzyme responsible for creating the new DNA strand by adding nucleotides to a primer RNA. It reads the template strand and matches the corresponding nucleotides, effectively constructing a new DNA strand in the 5’ to 3’ direction.

There are different types of DNA polymerase enzymes, each with a unique role during DNA replication. Some focus on replicating the leading strand, while others work on the lagging strand. Importantly, DNA polymerases also have proofreading abilities, checking and correcting mistakes as they go to ensure high fidelity in DNA replication.

• Synthesizes new DNA strands
• Works in 5' to 3' direction
• Proofreads to ensure accuracy

RNA primase

RNA primase plays an essential role in preparing the DNA template for replication. It synthesizes a short RNA segment, known as an RNA primer. This primer provides a starting point for DNA polymerase to begin DNA synthesis. Without this primer, the DNA polymerase would not be able to attach and start adding nucleotides.

During replication, multiple primers are laid down on the lagging strand to initiate synthesis of each Okazaki fragment. The presence of RNA primase is crucial as it sets the stage for DNA polymerase to efficiently build the DNA strand.

• Creates RNA primers
• Enables DNA polymerase attachment
• Essential for Okazaki fragment synthesis

DNA ligase

DNA ligase is tasked with sealing the nicks between neighboring DNA segments, particularly on the lagging strand during DNA replication. After DNA polymerase has filled in the DNA gaps left by the removal of RNA primers, small segments of DNA, known as Okazaki fragments, remain unlinked.

DNA ligase acts like a glue, joining these Okazaki fragments to form a continuous strand. This action is crucial for maintaining the structural integrity and continuity of the DNA molecule. Without DNA ligase, the completion and overall replication of the DNA strand would not be possible.

• Joins Okazaki fragments
• Ensures DNA continuity
• Maintains structural integrity of DNA