Introduction
Replication is the copying of DNA by end to end template synthesis it is based on complementary recognition of nucleotides
- 1953: watson and circle described double- helical structure
- DNA replication is semi Conservative because is composed of one old and one new Strand
- 1958 : In the famous Meselson–Stahl experiment of 1958 he and Frank Stahl demonstrated through nitrogen isotope labeling that DNA is replicated semi-conservatively. In addition, Meselson, François Jacob, and Sydney Brenner discovered the existence of messenger RNA in 1961
- Nucleotides are utilized in the form of triphosphates during DNA synthesis.
- Nucleotides are selected for joining based on complementary binding, where their bases form hydrogen bonds with exposed bases on the template DNA. This process is spontaneous and does not require energy or enzymes. Subsequently, DNA polymerase is needed to connect the nucleotides.
- Replication is→the copying of DNA by end to end template syntheses(its based on complementary recognition of nucleotides)
- What are some basic modes of replication ?
- Bubble : both strands of the parent DNA serve as template simultaneously the is majority of linear and circular DNAs
- Rolling Circle endonuclease produces a nick-single stranded cut in DNA, DNA polymerase binds and makes several circles and produces a long repeated leading strand. (the F factor Bactria)
- factor of bacteria
- D-loop : their 2 strands have different replication origins, newly synthesised DNA displaces old complementary strand this happens in the mitochondria and plastid genomes.
list and describe all the stages of DNA Replication (3 stages)↓
- Initiation:
- Replication begins at specific DNA sites called replication origins (Ori).
- Helicase unwinds the DNA double helix using ATP energy, creating a replication fork.
- Topoisomerase alters DNA supercoiling, preventing snapping back together.
- Single-strand binding proteins prevent fork closure.
- Elongation:
- DNA polymerase synthesizes a new DNA strand on top of the existing one by adding new nucleotides.
- Leading strand is synthesized continuously in the 5' - 3' direction by DNA polymerase.
- Lagging strand is synthesized discontinuously, forming Okazaki fragments.
- Primase synthesizes RNA primers, extended by DNA polymerase.
- DNA ligase joins Okazaki fragments together.
- Termination:
- Exonuclease removes RNA primers and replaces them with appropriate bases.
- DNA ligase joins Okazaki fragments to the growing strand.
- Telomerase solves end replication problem in linear DNA by adding missing flaps.
- Topoisomerases