Synthesis Phase (S phase)S phase in interphase of the cell
cycle.Nucleus of eukaryotes
DNA Nucleotide
Figure 11.7 Base Pairing in DNA Is Complementary
DNA ReplicationDNA must replicate during each cell divisionTHREE
alternative models for DNA replication were hypothesized:
Semiconservative replication Conservative replication Dispersive
replication
Figure 11.8
Watson & Crick predicted that each DNA strand could serve as
a template for the replication of a new strandQ: What is the mode
of replication?
The Mechanism of DNA ReplicationDNA replication is catalyzed by
DNA polymerase DNA polymerase needs an RNA primerDNA polymerase
adds nucleotides to the 3 end of the growing strandNucleotides are
added by complementary base pairing with the template strand
Figure 11.11
The Mechanism of DNA ReplicationMany proteins assist in DNA
replicationDNA helicases unwind the double helix, the template
strands are stabilized by other proteins
Figure 11.16
The Mechanism of DNA ReplicationMany proteins assist in DNA
replicationDNA helicasesRNA primase catalyzes the synthesis of
short RNA primers, to which nucleotides are added.DNA polymerase
III extends the strand in the 5-to-3 direction
Figure 11.15
RNA primase
The Mechanism of DNA ReplicationDNA synthesis on the leading
strand is continuous. It reads the template in the 3-to -5
direction (the same direction as helicase)The lagging strand grows
in the opposite direction to the Replication Fork. DNA is always
made in the 5-to-3 direction.Therefore, DNA synthesis on the
lagging strand is discontinuousDNA is created as short fragments
(Okazaki fragments) that are subsequently ligated together
Figure 11.17
The Mechanism of DNA ReplicationMany proteins assist in DNA
replicationDNA helicasesRNA primaseDNA polymerase IIIDNA polymerase
I degrades the RNA primer and replaces it with DNADNA ligase joins
the DNA fragments into a continuous daughter strand
