Question

What is the end replication problem?

Short answer

Answer: The end replication problem refers to the inability of the lagging strand to be fully replicated during DNA replication in linear DNA molecules, leading to their shortening with each round of cell division. This occurs because the RNA primers placed at the ends of the lagging strand cannot be replaced with DNA, as there is no space for DNA polymerase to attach and synthesize a new DNA strand. The problem is important because, if unchecked, the continuous shortening of DNA molecules may eventually lead to the loss of vital genes, causing cell death or malfunction. To counteract this issue, cells have evolved protective structures called telomeres and use an enzyme called telomerase to extend the ends of linear DNA molecules, preventing the loss of vital genetic information.

Step-by-step solution

Understanding DNA replication

DNA replication is a biological process where the two strands of a DNA molecule are separated, and each strand serves as a template to create a new complementary strand. This process is essential for cell division and ensures that the new cells contain the same genetic material as the original cell.

Leading and lagging strands in DNA replication

During DNA replication, one strand is synthesized continuously, known as the leading strand, while the other strand is synthesized discontinuously, known as the lagging strand. The lagging strand is synthesized in small fragments called Okazaki fragments, which are then joined together by DNA ligase enzymes.

Importance of the DNA replication ends

Since DNA replication occurs in two different directions, this causes a problem when it reaches the ends of a linear DNA molecule. In particular, the lagging strand cannot be fully synthesized because there is no place to start making the latest Okazaki fragment as the replication reaches the very end of the strand.

Understanding the end replication problem

The end replication problem refers to the fact that the lagging strand is unable to be fully replicated during DNA replication, which leads to the shortening of linear DNA molecules every time the cell divides. This shortening occurs because the RNA primers placed at the ends of the lagging strand cannot be replaced with DNA, as there is no space for DNA polymerase to attach and synthesize a new DNA strand. As a consequence, after each round of replication, the lagging strand loses a small portion from its end.

Consequences of the end replication problem

The end replication problem is important because if a DNA molecule continues to shorten with each round of replication, eventually, vital genes will be lost, causing cell death or malfunction. To prevent this issue, cells have evolved protective structures called telomeres, which are non-coding, repetitive DNA sequences that act as a "buffer zone" at the ends of chromosomes. These telomeres protect the coding regions from the end replication problem and can be extended by an enzyme called telomerase.