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DNA is defined by containing 2'-deoxy-ribose nucleic acid while RNA is defined by containing ribose nucleic acid. [1] In some occasions, DNA and RNA may contain some minor bases. Methylated forms of the major bases are most common in DNA. In viral DNA, some bases may be hydroxymethylated or glucosylated.
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.
The eukaryotic cell cycle consists of four distinct phases: G 1 phase, S phase (synthesis), G 2 phase (collectively known as interphase) and M phase (mitosis and cytokinesis). M phase is itself composed of two tightly coupled processes: mitosis, in which the cell's nucleus divides, and cytokinesis, in which the cell's cytoplasm and cell membrane divides forming two daughter cells.
During DNA replication, the replisome will unwind the parental duplex DNA into a two single-stranded DNA template replication fork in a 5' to 3' direction. The leading strand is the template strand that is being replicated in the same direction as the movement of the replication fork.
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.
A primer binding site is a region of a nucleotide sequence where an RNA or DNA single-stranded primer binds to start replication. The primer binding site is on one of the two complementary strands of a double-stranded nucleotide polymer , in the strand which is to be copied, or is within a single-stranded nucleotide polymer sequence.
At the G1/S checkpoint, p53 acts to ensure that the cell is ready for DNA replication, while at the G2/M checkpoint p53 acts to ensure that the cells have properly duplicated their content before entering mitosis. [40] Specifically, when DNA damage is present, ATM and ATR kinases are activated, activating various checkpoint kinases. [41]
The DNA re-replication response is different from the response taken when damage is due to oxygen radical generation. Damage from oxygen radical generations leads to a response from the Myc oncogene, which phosphorylates p53 and H2AX. [16] The ATM/ATR DNA damage network will also respond to cases where there is an overexpression of Cdt1.