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DNA replication occurs on multiple origins of replication along the DNA template strands. As the DNA double helix is unwound by helicase, replication occurs separately on each template strand in antiparallel directions. This process is known as semi-conservative replication because two copies of the original DNA molecule are produced, each copy ...
DNA was extracted periodically and was compared to pure 14 N DNA and 15 N DNA. After one replication, the DNA was found to have intermediate density. Since conservative replication would result in equal amounts of DNA of the higher and lower densities (but no DNA of an intermediate density), conservative replication was excluded.
The process of semiconservative replication for the site of DNA replication is a fork-like DNA structure, the replication fork, where the DNA helix is open, or unwound, exposing unpaired DNA nucleotides for recognition and base pairing for the incorporation of free nucleotides into double-stranded DNA.
Eukaryotes initiate DNA replication at multiple points in the chromosome, so replication forks meet and terminate at many points in the chromosome. Because eukaryotes have linear chromosomes, DNA replication is unable to reach the very end of the chromosomes. Due to this problem, DNA is lost in each replication cycle from the end of the chromosome.
[4] [5] This process is considered semi-conservative because, after replication, each copy of DNA contains a strand from the original DNA molecule and a strand from the newly-synthesized DNA molecule. [5] An RNA primer is a short chain of single-stranded RNA, consisting of roughly five to ten nucleotides complementary to the DNA template strand.
The temporal order of replication of all the segments in the genome, called its replication-timing program, can now be easily measured in two different ways. [1] One way simply measures the amount of the different DNA sequences along the length of the chromosome per cell.
Reassembly of nucleosomes behind the replication fork is mediated by chromatin assembly factors (CAFs) that are loosely associated with replication proteins. [4] [11] Though not fully understood, the reassembly does not appear to utilize the semi-conservative scheme seen in DNA replication. [11]
DNA replication also works by using a DNA template, the DNA double helix unwinds during replication, exposing unpaired bases for new nucleotides to hydrogen bond to. Gene synthesis, however, does not require a DNA template and genes are assembled de novo. DNA synthesis occurs in all eukaryotes and prokaryotes, as well as some viruses. The ...