What is a replication bubble?




A.A complex of replication enzymes on the DNA template strand



B.A DNA sequence that initiates replication



C.A tangle of denatured DNA strands near the replication fork



D.A locally denatured segment of DNA where replication originates



E.A localized site in the nucleus where chromosomes are replicating

The correct answer is D. A replication bubble is a locally denatured segment of DNA where replication originates.

To understand what a replication bubble is, it's important to first understand the process of DNA replication. DNA replication is the process by which a cell makes an exact copy of its DNA. It occurs during the S phase of the cell cycle.

During replication, the DNA double helix is unwound and separated into two strands by an enzyme called helicase. This separation of the two DNA strands creates a structure called the replication fork. The replication fork is the Y-shaped structure that forms as the DNA strands separate.

At the replication fork, DNA replication occurs bidirectionally. The synthesis of the new DNA strand proceeds in opposite directions on the two template strands of DNA. This creates two replication forks moving in opposite directions along the DNA molecule.

In order for DNA replication to occur, the double-stranded DNA must be unwound and separated into single strands. This is done by an enzyme called DNA helicase. As DNA helicase separates the DNA strands, it creates a region of locally denatured DNA called a replication bubble.

The replication bubble is a region where the two DNA strands have been separated and the DNA helicase is actively unwinding the DNA. It is at this site that DNA replication originates. The two replication forks move in opposite directions from the replication bubble, each synthesizing a new DNA strand complementary to the template strand.

In summary, a replication bubble is a locally denatured segment of DNA where replication originates. It is a result of the unwinding and separation of the DNA strands by DNA helicase at the replication fork.