DNA replication is the semi-conservative process by which a cell makes an exact copy of its DNA. It works through complementary base pairing between nucleotides on each strand. The Meselson-Stahl experiment provided support for this semi-conservative model. During replication, helicase unwinds the double helix and separates the two strands. DNA polymerase then links new nucleotides to each old strand using them as templates to build new complementary strands. The leading strand is replicated continuously while the lagging strand is replicated discontinuously in segments that are later joined by ligase.

1. IB Biology Chapter 2 Notes: DNA Replication (2.7 & 7.1) NAME:
Word Definition
Template Something that serves as a model for others to copy
Nucleoside tri-
phosphate
Nucleotide with three phosphates instead of 1. Has high energy bond (like ATP)
Leading strand The strand of DNA that is replicated continuously
Lagging strand The strand of DNA that is replicated discontinuously, in segments
Okazaki fragments The segments of DNA made in the lagging strand
Mutation A change in the DNA sequence (base sequence)
Semi-conservative The model of DNA replication where one old strand is paired with one new strand
Replication fork
(bubble, origin of
replication)
The place(s) where replication starts
DNA replication The process of copying the DNA in a cell to make an exact copy
Helicase The enzyme that unzips DNA
DNA Polymerase III The enzyme that adds complementary nucleotides to the template strand in a 5’ 3’
direction
DNA Polymerase I The enzyme that replaces the RNA primer nucleotides with DNA nucleotides
DNA Primase The enzyme that creates the RNA primer
DNA ligase The enzyme that “glues” together the backbone of the new DNA strands (okasaki
fragments or where primer was)
Single-Stranded
Binding Proteins
Proteins that keep the single strands of DNA separated long enough to allow them to
be copied during replication.
DNA Gyrase
(Topoisomerase)
The enzyme that guides and stabilizes the unwinding of the DNA double helix

2. 2.7.1 The replication of
DNA is semi-conservative
and depends on
complimentary base-pairing.
2.7.12 Analysis of Meselson
and Stahl’s results to obtain
support for the theory of
semi-conservative
replication of DNA.
2.7.2 Helicase unwinds the
double helix and separates
the two strands by breaking
hydrogen bonds.
2.7.3 DNA polymerase links
nucleotides togetherto form
a new strand,using the pre-
existing strand as a template.
2.7.9 Use of Taq DNA
polymerase to produce
multiple copies of DNA
rapidly by the polymerase
chain reaction (PCR).
What occurs in DNA replication?
What does it mean that DNA replication is semi-conservative?
What is complimentary base-pairing?
Describe the Meselson-Stahl experiment:
Describe the structure and function of Helicase:
Describe the structure and function of DNA Polymerase:
What is the Polymerase Chain Reaction (PCR)?
Outline what the steps that occur in PCR:
What is Taq Polymerase?

3. 7.1.1 DNA structure
suggested a mechanism for
DNA replication.
7.1.3 DNA replication is
continuous on the leading
strand and discontinuous on
the lagging strand.
7.1.4 DNA replication is
carried out by a complex
series of enzymes.
7.1.5 DNA polymerases can
only add nucleotides to the
3’ end of a primer.
7.1.9 Use of nucleotides
containing
dideoxyribonucleic acid to
stop DNA replication in
preparation of samples for
base sequencing.
Leading strand:
Lagging strand:
Enzyme Function
DNA Topoisomerase
Single Stranded
Binding Proteins
Helicase
DNA Polymerase III
Primase
DNA Polymerase I
DNA Ligase