WHAT IS SEMI-CONSERVATIVE DNA REPLICATION
Semi-conservative DNA replication is the process of DNA synthesis in which each strand of the original double helix acts as a template for a new complementary strand. During replication, the double helix of DNA is separated into two strands by an enzyme called helicase. Each single strand then serves as a template for the synthesis of a new complementary strand by DNA polymerase. The end result is two identical double-stranded DNA molecules, each containing one original parental strand and one newly synthesized daughter strand. This mode of replication was first proposed by Watson and Crick in 1953, and it has been extensively studied and confirmed since then.
Semi-conservative DNA replication is the process by which DNA molecules are duplicated. It was first proposed by James Watson and Francis Crick in 1953, based on data gathered by Matthew Meselson and Franklin Stahl in 1958.
During semi-conservative DNA replication, the DNA double helix unwinds and the two strands separate. Each separated strand serves as a template for the synthesis of a new complementary strand. The replication process occurs in the following steps:
1. Initiation: The replication begins at specific sites on the DNA molecule called origins of replication. At the origin, enzymes called helicases unwind and separate the DNA strands, forming a replication fork.
2. Elongation: DNA polymerase enzymes move along each separated DNA strand in opposite directions. One strand, known as the leading strand, is synthesized continuously, while the other strand, known as the lagging strand, is synthesized discontinuously in short fragments called Okazaki fragments.
3. Priming: Before DNA polymerase can begin synthesizing a new DNA strand, a short segment of RNA called a primer is added by another enzyme called primase. This provides a starting point for DNA polymerase to begin adding nucleotides.
4. Base pairing: DNA polymerase adds nucleotides to the growing DNA strand by following the base-pairing rules. Adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).
5. Proofreading and repair: Throughout the replication process, DNA polymerase performs proofreading, meaning it checks for errors and corrects them. In case of errors that are not fixed during replication, DNA repair mechanisms play a role in correcting the mistakes.
6. Termination: The replication process continues until the entire DNA molecule is replicated. At the termination point, specific sequences called termination sites signal the completion of replication.
After semi-conservative DNA replication is complete, each resulting DNA double helix consists of one original, or parental, strand and one newly synthesized strand. This is why it is called "semi-conservative," as half of the original DNA molecule is conserved in each daughter DNA molecule.
Overall, semi-conservative DNA replication ensures the faithful duplication of genetic information and is essential for cell division, growth, and development.