The DNA replication machinery in a human can copy approximately 6.5 billion bases in a few hours. It can operate so quickly in part because:
a) multiple ribosomes can attach to a single message, forming a polysome that greatly speeds up translation.
b) Okazaki fragments are pre-formed by the action of DNA polymerase I and DNA ligase, and so can be added rapidly to the leading strand.
c) RNA polymerase is capable of copying the DNA template at >5 million bases/chromosome/hour.
d) DNA replication is initiated simultaneously at many points along each chromosome.