Question

Topoisomerases are enzymes involved in: (A) DNA replication and transcription. (B) posttranscriptional processing. (C) RNA synthesis and translation. (D) posttranslational processing.

Short answer

(A) DNA replication and transcription.

Step-by-step solution

- Understanding the role of Topoisomerases

Topoisomerases are enzymes that help manage DNA supercoiling and tangling. They work by cutting and rejoining DNA strands to relieve tension created during DNA replication and transcription.

- Elimination of incorrect options based on function

Topoisomerases are not directly involved in posttranscriptional processing (B), RNA synthesis and translation (C), or posttranslational processing (D). These processes involve other specific enzymes and machinery.

- Confirming the correct option

Given their role in managing DNA supercoiling, topoisomerases are primarily involved in (A) DNA replication and transcription.

Key concepts

Topoisomerases: Unsung Heroes of DNA Processing

Topoisomerases play a crucial role in both DNA replication and DNA transcription by relieving the torsional stress generated as the DNA double helix unwinds. These enzymes cut the DNA strands, allow them to untwist, and then rejoin the strands. This action is critical because it prevents the DNA from becoming supercoiled, which could make the replication or transcription processes halt or proceed with errors.

There are two main types of topoisomerases: Type I and Type II.

• Type I topoisomerases cut one strand of the DNA, leading to the release of excess twists and then rejoining the strand.
• Type II topoisomerases cut both strands, which allows for the separate DNA helices to pass through one another, alleviating supercoiling on a larger scale.

Their ability to manage the shape and tension of DNA is what keeps the genomic processes running smoothly.

DNA Replication

DNA replication is the process by which a cell copies its entire genome before cell division. This ensures that each daughter cell receives an exact copy of the parent cell's DNA.

During replication, the double helix structure of the DNA is unwound by an enzyme called helicase. This creates a replication fork with two single DNA strands. Topoisomerases come into play to prevent the upstream DNA from becoming too tightly supercoiled as it is unwound.

Primase lays down a primer, which is a short RNA segment, to provide a starting point for DNA polymerase. DNA polymerase then attaches to the primer and starts synthesizing the new DNA strand by adding complementary nucleotides to the original strands. This results in two identical double helices, each consisting of one old strand and one newly synthesized strand.

DNA Transcription

DNA transcription is the process by which a specific segment of DNA is copied into RNA. This RNA can then be used as a template for protein synthesis.

Just like in DNA replication, helicase unwinds the DNA strand during transcription. Topoisomerases again are essential as they alleviate the supercoiling tension that arises when the DNA double helix is unwound.

RNA polymerase binds to a promoter region on the DNA and starts synthesizing RNA by adding RNA nucleotides complementary to one of the DNA strands. This RNA, called messenger RNA (mRNA), is a single-stranded molecule that undergoes further processing before being translated into proteins. The coordinated action of these enzymes ensures that cells efficiently manage their genetic information, allowing for proper gene expression and cellular function.