Question

Topoisomerases are enzymes involved in A. DNA replication. B. DNA transcription. C. RNA processing. D. RNA translation.

Short answer

A. DNA replication.

Step-by-step solution

Identify the Role of Topoisomerases

Topoisomerases are enzymes that help manage DNA supercoiling and prevent tangling during DNA processes.

Determine Which Processes Involve DNA

Among the options, DNA replication and DNA transcription both involve DNA.

Focus on DNA Replication Role

During DNA replication, topoisomerases help by relieving the tension that builds up as the DNA helix unwinds. This is their primary function.

Exclude Non-DNA Processes

Since RNA processing and RNA translation do not directly involve managing DNA supercoiling, these options can be excluded.

Select the Correct Answer

Based on the role of topoisomerases in managing DNA supercoiling during replication, the correct answer is A. DNA replication.

Key concepts

DNA replication

DNA replication is the process by which a cell copies its DNA before it divides. This ensures that each new cell has the exact same genetic material.
During replication, the double-stranded DNA helix unwinds to form two single strands. These strands serve as templates for creating new, complementary strands.
Enzyme helicase opens up the double helix by breaking hydrogen bonds between base pairs. Single-strand binding proteins then stabilize the unwound DNA.
The enzyme DNA polymerase adds new nucleotides to form the new strand, using the original strand as a template. Primase synthesizes a short RNA primer to kickstart this process.
Topoisomerases play a critical role during DNA replication by relieving the tension that builds up as the helix unwinds.

In simple terms, they act like a pair of scissors, cutting the DNA strands to release the tension and then rejoining them. This helps prevent the DNA from becoming too twisted, which can impede replication. Proper function of these enzymes is vital to ensure accurate and efficient replication.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are crucial for life and perform a wide variety of functions.
Enzymes are highly specific to the reactions they catalyze. Their shape allows them to bind to specific molecules called substrates. This binding occurs at a region on the enzyme called the active site.
The enzyme's specificity ensures it can perform its function without affecting other molecules or reactions. Once the reaction is complete, the enzyme releases the products and is ready to catalyze another reaction.
In the context of DNA replication, several enzymes are involved alongside topoisomerases:

• Helicase: Unwinds the DNA double helix.
• DNA polymerase: Adds new nucleotides to form the new DNA strand.
• Primase: Synthesizes an RNA primer to initiate DNA synthesis.
• Ligase: Joins Okazaki fragments on the lagging strand.

These enzymes must work in a coordinated fashion to ensure the DNA replication process occurs smoothly and accurately.

DNA supercoiling

DNA supercoiling refers to the twisting of the DNA double helix upon itself. This can occur naturally or be induced by various physiological processes.
Supercoiling is important because it helps DNA fit within the limited space of the cell nucleus. However, during DNA replication and transcription, negative supercoiling causes the DNA ahead of the replication fork to become overwound and create tension.
Topoisomerases are essential in managing DNA supercoiling. They function by cutting one or both strands of the DNA helix to relieve the tension, allowing the strands to be untwisted, and then rejoining the DNA strands.
There are two main types of topoisomerases:

• Type I topoisomerase: Cuts one strand of DNA, allows it to unwind, and then reseals the cut.
• Type II topoisomerase: Cuts both strands of DNA and allows passage of another segment of the double helix through the break before resealing.

This cutting and rejoining mechanism is essential for preventing knots and tangles, ensuring that DNA processes, such as replication and transcription, proceed efficiently.