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DNA:
Genetic Material
Review:
 All
living things must have genetic
material Species must be able to
pass on that genetic material to
future generations.
DNA: Deoxyribonucleic acid
 It is located in the nucleus of cells in
eukaryotes.
 It is found in the cytoplasma of prokaryotes
 It is the blueprint that makes you who you
are.
 It is described as a double helix.
DNA: Deoxyribonucleic acid
DNA is a type of organic compound.
 It is used for storing and transmitting genetic info
 It is found in in all living organisms
 Eukaryotes – in nucleus only.
 Prokaryotes - free floating.
The Structure of DNA
Building Blocks of DNA
Nucleotides: subunits that make up the
extraordinarily long thin molecule of DNA.
Each nucleotide consists of three parts:
A phosphate group
A five-carbon sugar molecule
A nitrogen base
Building Blocks of DNA
 The five-carbon sugar
molecule is called
deoxyribose.
 The phosphate group is
attached to the sugar and
is the same for all
molecules of DNA.
 These two molecules form
the backbone of a DNA
strand.
Building Blocks of DNA
The nitrogen base found in each nucleotide of
the DNA molecule is one of four different bases:




Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
Chargaff’s Rule
 Adenine must pair with
Thymine
 Guanine must pair with
Cytosine
 The bases form weak
hydrogen bonds
T
G
A
copyright cmassengale
C
9
Building Blocks of DNA
Purines: a class of organic
molecules that have a double ring of
carbon and nitrogen atoms
 Adenine
 Guanine
Building Blocks of DNA

Pyrimidines: a
class of organic
molecules that have
a single ring of
carbon and nitrogen
– Thymine
– Cytosine
Chargarff’s Rules

Base pairing rules: for
the DNA in each
Organism
– The amount of guanine
always equals the amount
of cytosine (number of G
= number of C)
– The amount of adenine
always equals the amount
of thymine (number of A =
number of T)
Why are the bases so picky?
DNA is a Double Helix
1953: Watson and Crick
 Using the base pairing rule
and X-ray photos from
1950 made a 3-D model
using tin and wire.
 The result was the double
helix, a “spiral staircase”
configuration
DNA is a Double Helix
The Double Helix Model:
 It has a sugar and phosphate
backbone
 Adenine pairs with Thymine
Guanine pairs with Cytosine
 The nitrogen bases are held
together by hydrogen bonds.
 Due to the base pairing the
two strands are
complementary to each other
DNA is a Double Helix
Write the complementary
strand for the following
sequence
AGTCCTGAAATCGG
TCAGGACTTTAGCC
DNA Replication
Before a cell can divide:

the DNA in the nucleus of the
cell must be copied.

this process is called
Replication

Replication ensures that each
new cell receives an exact
copy of the cells genetic
information.
DNA Replication
 During Replication the DNA molecule “untwists” into
two strands or replication forks.
 The separation occurs at the hydrogen bonds between
the nitrogenous bases.
DNA Replication
 The separation of the
replication fork is
accomplished by an
enzyme called Helicase.
 The helicase breaks
the DNA molecule into
two strands
DNA Replication
The original individual strands serve as a template
for the building of two new complimentary strands
of DNA
DNA Replication
Polymerase an enzyme, joins new nucleotides to
each existing strand according to the base pairing
rule:
Adenine >Thymine and Guanine > Cytosine
DNA Replication
 The two new molecules
“re-twist”
 Each new DNA molecule
consists of one original
strand and 1 new strand
 As a result DNA
Replication is said to be
semi- conservative
DNA Replication Practice
Using the base pairing rule what complimentary
strand would produced from the following DNA
base sequence(s)
A
C
T
__ __ __
G
__
G
__
C
__
A
__
C
__
G
__
A G
__ __
T
__
A
__
T
__
A
__
C
__
C
__
G
__
DNA Replication Practice
A DNA molecule is 60 nucleotide bases long. 40 of the nucleotide
bases are identified as adenine. How many thymine nucleotides
must there be in this DNA molecule? How many Cytosine? Guanine?
Adenine __ Thymine __ Cytosine __ Guanine __
A DNA molecule is 100 nucleotide bases long. 20 of the
nucleotide bases are identified as Guanine. How many Cytosine
nucleotides must there be in this DNA molecule? How many
Adenine? Thymine?
Adenine __ Thymine __ Cytosine __ Guanine __