DNA
Replication Overview
DNA replication is an essential aspect of cellular and viral reproduction. Replication of a double-stranded DNA results in two double-stranded DNAs as products. Some important general points about DNA replication are as follows:
The mechanism of replication is semi-conservative--each newly made strand is copied from one of the parental strands and the products of replication are two molecules, each containing one parental strand and one newly synthesized strand (see here).
DNA replication intermediates contain "forked" structures at the site of replication (Figure 24.1).
Replication is orderly and sequential--it begins at a fixed point (called an origin) and closely follows parental duplex unwinding.
DNA replication uses deoxyribonucleoside-5'-triphosphates (dNTPs) to build the DNA chains.
DNA replication is discontinuous--synthesis of one strand (called the lagging strand) lags behind the other (called the leading strand) and occurs in pieces called Okazaki fragments (Figure 24.4). Replication of the leading strand is continuous (Figure 24.3).
Replication is exceedingly accurate--far more accurate than any other enzyme-catalyzed process.
Replication can be broken down into three processes--initiation, elongation, and termination.
Multiple proteins are required for DNA replication at a replication fork. These include DNA polymerases, single-strand DNA binding proteins, helicases, primase, topoisomerases, and DNA ligase. Some of these are multisubunit protein complexes.
DNA polymerase catalyzes the chemical reaction of DNA synthesis (Figure 24.2).
DNA chain growth (replication) proceeds only in the 5' to 3' direction.