1. Initiation:
- DNA replication starts at specific locations in the DNA molecule called the origins of replication.
- Enzymes called helicases break the hydrogen bonds between complementary base pairs, causing the DNA double helix to "unzip" and unwind, creating two replication forks.
2. Elongation:
- Each replication fork serves as a template for DNA synthesis.
- An enzyme called DNA polymerase reads the template strand from the 3' to 5' direction.
- It catalyzes the addition of complementary nucleotides to the growing DNA molecule.
- The nucleotides are added one by one, matching with their complementary bases (A with T, G with C) according to the base-pairing rules.
- This process continues, resulting in the elongation of the new DNA strands.
3. Leading and Lagging Strands:
- As the DNA unwinds at the replication fork, it creates a "Y" shape.
- One strand, known as the leading strand, is synthesized continuously towards the replication fork.
- The other strand, called the lagging strand, is synthesized discontinuously in small fragments known as Okazaki fragments.
- These fragments are later joined together by an enzyme called DNA ligase.
4. Termination:
- DNA replication proceeds until the entire DNA molecule has been copied.
- It ends when special sequences, called telomeres, are reached at the ends of the chromosomes.
- Telomeres protect the ends of DNA and prevent them from unraveling.
5. Proofreading and Repair:
- DNA polymerases have proofreading capabilities to minimize errors during replication.
- They can detect incorrect nucleotide insertions and remove them.
- Additionally, other repair mechanisms identify and correct any errors that escape the proofreading process.
6. Completion and Cell Division:
- Once DNA replication is complete, two identical copies of the original DNA molecule are produced.
- During cell division (mitosis), these copies are distributed to the daughter cells, ensuring that each new cell receives its own complete set of genetic material.
Overall, DNA replication is a tightly regulated and highly accurate process that ensures faithful transmission of genetic information during cell division and reproduction.
