DNA, Gene Structure, and DNA Replication - Insect Molecular Genetics - page 20

Figure 1.10 DNA replication is semiconservative, meaning that each new DNA helix contains one
old and one new complementary strand. DNA synthesis relies on complementary base pairing to
replicate DNA accurately.
polymerases have two properties that complicate DNA synthesis. First, DNA
polymerase can synthesize only in the 5 ′ to 3 ′ direction; and, second, DNA poly-
merase cannot initiate the synthesis of new DNA strands without a primer .
1.16 DNA Replication Occurs Only in the 5 ′ to 3 ′ Direction
Because DNA polymerases can synthesize DNA only in the 5 ′ to 3 ′ direction, the
template strands must be read in the 3 ′ to 5 ′ direction ( Box 1.1 ). This process is
straight-forward for one of the DNA template strands, called the leading strand ,
and DNA synthesis can proceed in an uninterrupted manner the entire length of
the leading strand. However, DNA synthesis cannot proceed uninterrupted on
the other template strand, called the lagging strand ( Figure 1.12 ). DNA synthesis
on the lagging strand is discontinuous, occurring in short sections, and produces
short fragments (100-200nt in length) of DNA called Okazaki fragments , after
their discoverer who identified them in 1968 ( Ogawa and Okazaki 1980 ).