Microbiology Demystified

replication. DNA is replicated by taking one parent double-stranded DNA mol-
ecule, unzipping it and building two identical daughter molecules. Bases along
the two strands of double-helical DNA complement each other. One strand of the
pair acts as a template for the other.
DNA is replication requires complex cellular proteins that direct the sequence
of replication. Replication begins when the parent double-stranded DNA mole-
cule unwinds; then the two strands separate. The DNA polymerase enzyme uses
a strand as a template to make a new strand of DNA. The DNA polymerase
enzyme examines the new DNA and removes bases that do not match and then
continues DNA synthesis.
The point at which the double-stranded DNA molecule unzips is called
the replication fork (Fig. 7-1). The two new strands of DNA each have a base

CHAPTER 7 Microbial Genetics^121

Parental helix

G C

AT

G

C

TA

TA

GC

AT

A

T A

C G

CG

AT

AT

G

GC

AT

T A

CG

C

TA

A T

GC

New New Parental

5 ′ 3 ′

3 ′ 5 ′ 3 ′ 5 ′

Parental

AT

AT

GC

AT

T A

CG

C

TA

A T

G C

Replication fork

Replicas

G

Fig. 7-1. In semiconservative replication, new strands are synthesized

after the replication fork.