Overview of DNA Replication
DNA replication is the process by which a cell copies its entire DNA genome before cell division, ensuring each daughter cell receives an identical set of genetic instructions. This semi-conservative mechanism, first described by Watson and Crick, involves unwinding the double helix and synthesizing two new strands using the original as templates.
Key Steps in the Replication Process
The process begins at origins of replication where helicase enzymes unwind the DNA double helix, creating replication forks. Primase adds RNA primers, and DNA polymerase synthesizes new strands: leading strand continuously in the 5' to 3' direction, while the lagging strand forms Okazaki fragments. Ligase joins these fragments, and proofreading enzymes correct errors for fidelity.
Practical Example in Eukaryotic Cells
In human cells during mitosis, DNA replication occurs in the S phase of the cell cycle. For instance, a skin cell preparing to divide replicates its 6 billion base pairs of DNA, allowing two identical daughter cells to form for tissue repair. Errors here could lead to mutations, as seen in cancer development if proofreading fails.
Importance in Cell Division and Beyond
DNA replication is essential for cell division (mitosis and meiosis), enabling growth, tissue maintenance, and reproduction. It preserves genetic integrity across generations; without accurate replication, organisms couldn't evolve or adapt. In medicine, understanding this process aids treatments for genetic disorders and cancer therapies targeting replication enzymes.