What is semi conservative replication?
Semi-conservative replication is a type of DNA replication in which each newly synthesized double-stranded DNA molecule consists of one original (conserved) strand and one newly synthesized strand. This means that during DNA replication, the two strands of the double helix separate and each strand serves as a template for the synthesis of a new complementary strand. Each new DNA molecule produced has one strand from the original DNA molecule and one newly synthesized strand. This process ensures the genetic continuity of the cell across generations.
Semi-conservative replication is a process of DNA replication that was proposed by James Watson and Francis Crick in 1953 when they described the structure of DNA. It refers to the mechanism by which DNA makes copies of itself.
In semi-conservative replication, the double-stranded DNA helix unwinds and separates into two individual strands. Each separated strand then serves as a template for the synthesis of a new complementary strand. As a result, each new DNA molecule formed after replication contains one original (parental) strand and one newly synthesized (daughter) strand.
The process of semi-conservative replication involves several steps:
1. Initiation: DNA replication starts at specific sites on the DNA molecule called origins of replication. Enzymes called helicases unwind and separate the double helix at these sites.
2. Elongation: An enzyme known as DNA polymerase adds nucleotides to the new strand according to the base-pairing rules (A with T, G with C). It moves along the parent DNA strand in the 3' to 5' direction, synthesizing the new complementary strand in the 5' to 3' direction.
3. Priming: Before DNA polymerase can start adding nucleotides, a short RNA primer is synthesized by an enzyme called primase. This primer provides a starting point for DNA polymerase to initiate DNA synthesis.
4. Leading and Lagging Strand Synthesis: DNA replication occurs differently on the two template strands. On the leading strand, DNA synthesis proceeds continuously in the same direction as the replication fork. On the lagging strand, DNA synthesis occurs in small fragments called Okazaki fragments, which are later joined together by an enzyme called DNA ligase.
5. Termination: DNA replication concludes when the entire DNA molecule has been replicated. The replication forks eventually meet at the termination sites, and the newly synthesized DNA strands are sealed.
By conserving one parental strand in each newly synthesized DNA molecule, semi-conservative replication ensures the preservation of genetic information across generations and accurate replication of the DNA molecule.