DNA Replication
Inquiry into Life – pg. 489-493
Today’s Objectives:
 Describe DNA Replication, including:
 Describe the three steps in the semi-conservative replication of DNA:
 “unzipping” (DNA helicase)
 Complementary base pairing (DNA polymerase)
 Joining of adjacent nucleotides (DNA polymerase)
 Describe the purpose of DNA replication
 Identify the site of DNA replication within the cell
Background information
 It is important to recall the information we learned about DNA from the last 2 units:
 DNA stands for ________________________
 DNA is the molecule that makes up _______________ and serves as
________________information
Nucleic Acids
 There are two types of nucleic acids, _____and _____
 Both DNA and RNA are ____________ of
_________________ (chains of joined nucleotides)
 They form ___________ material and are involved in
the functioning of _______________ and protein
____________
 DNA Structure:
 The shape of DNA is a __________ _________ made
up of repeating nucleotide units
Nucleotide Structure
 Nucleotides are composed of 3 parts:
 1) ______________ molecule
 2) ________________
 Deoxyribose in DNA
 Ribose in RNA
 3) ___________ containing _______
Nitrogen containing bases
 Two types:
 ___________ – adenine (A) and guanine (G)
 _______________ – thymine (T), uracil (U) and cytosine (C)
 DNA has A,G,T,C, RNA has A,G,U,C
 Purines are __________ than pyrimidines and have a __________ ring structure
 Pyrimidines are __________ than purines and have a ________ ring structure
 When the bases bond together to form the “rungs of the DNA _________” they do so in
a set pattern.
 The alternating sugar and phosphates make up the _______ (_____________).
 The bases make up the _________.
Complementary Base Pairing
 ____________ always bonds to ___________
 ______ hydrogen bonds
 _________ always bonds to _________
 ________ hydrogen bonds
 This bonding of bases is called
___________________ base pairing
 They cannot bond any other way because 2
purines would __________ and 2 pyrimidines would
be too _________ to form the rungs of the ladder
The double strand is held in place by hydrogen bonds
between the bases.
It is the ____________ and ________ as well as the
________ of the bases that determine what kind of
____________ will develop.
Order of Bases
 Example:
 ATCCGATT means something entirely different than ACCGTTAT,
just as the words hate and heat mean different things even
though they contain the same letters
 As a DNA strand lengthens, it twists into a double spiral called a
__________ ________
Candy DNA Model
 Next class you will build a DNA molecule using CANDY! (you can
eat it after you are finished)
Functions of DNA
 1) _____________ (duplicates) itself so each new cell has a
complete, ____________ copy
 2) ____________ the activities of a cell by producing ____________
 The combination of proteins determines the characteristics of each living
organism
 3) Undergoes occasional _____________ (mistakes in replication) which accounts for the
_________ of living things on earth
DNA Replication
 Steps in DNA Replication:
1. The DNA molecule becomes untwisted by the enzyme _______ ___________ breaking the
H-bonds. The 2 strands that make up DNA become _____________. Each side acts as a
_____________. (ie. The weak hydrogen bonds between the paired bases are broken by an
enzyme)
2. New complementary ________________, always present in the nucleus,
move into place and pair with complementary bases on the ___________
__________.
 ___ joins to ___
 ___ joins to ___
3. The ____________ nucleotides, through their sugar-phosphate
components become ___________ together along the newly
forming chain. The enzyme _______ _______________ helps this.
(Adds nucleotides to template).
4. When the process is finished, 2 ______________ DNA
molecules are present, ____________to each other and to the
___________ molecule.
5.
Both DNA will now wind back up into their _________ shape.
 DNA replication is called __________________________ because each new double helix
is composed of an old (___________) strand and a new (____________) strand.
 Each strand conserves a length of the old strand
 ___________ assist the ___________ process, _______ together the nucleotides, and
assist the ______________ process and many others.
 When errors are made in replication. A ___________ can arise.