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Bellringer
Key Ideas
DNA: The Genetic Material
Searching for the Genetic Material
The Shape of DNA
The Information in DNA
Discovering DNA’s Structure
Summary
Section 1: The Structure of DNA
DR 13.1. Section: The Structure of DNA
Read each question, and answer based upon what you learn in the section.
1. With what kinds of bacteria did Griffith inject mice?
2. What was different about the S bacteria and the R bacteria?
3. Why were the heat-killed S bacteria harmless?
4. Why was the mixture of heat-killed S bacteria and R bacteria virulent?
5. What did Griffith discover as a result of his experiments?
6. How did Avery discover that the material responsible for transformation in bacteria
was DNA?
7. Viruses that infect bacteria are called [bacteriophages / rough].
8. A virus is made of DNA and [proteins / cell walls].
9. Radioactive sulfur was used to label the [DNA / protein] in the viruses.
10. Radioactive phosphorus was used to label the [DNA / protein] in the viruses.
11. Hershey and Chase discovered that after the 32P-labeled phages infected the
bacteria, most of the radioactive phosphorus was found in the layer containing
[bacteria / phage].
Match the letter of the phrase with the appropriate term
_____ 12. double helix
a. a five-carbon sugar
_____ 13. nucleotides
b. type of weak bond between base pairs that holds the double helix
_____ 14. deoxyribose
together
_____ 15. hydrogen bond
c. four kinds and they form specific pairs
_____ 16. nitrogenous bases d. subunits that make up DNA
e. one of two pyrimidines used as a nitrogenous base in nucleotides
_____ 17. adenine
f. one of two purines used as a nitrogenous base in nucleotides
_____ 18. cytosine
g. discovered that the amount of adenine always equaled the amount of
_____ 19. Chargaff
cytosine and that guanine always equaled cytosine
h. two strands of nucleotides twisted around each other
Explain how the terms in each pair are related to each other.
20. base-pairing rules, complementary
21.Wilkins and Franklin, DNA structure
This is DNA.
 What do you
know about
it?
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DNA
What is its job & why
is it important?
 How was it
discovered?
 What is its structure?
 How does it get
created/duplicated?
 How does the
information contained
therein get accessed?
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Heredity is one of the 7 properties of life.
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What is this?
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How is the passing of traits from parents
to offspring achieved?
Properties of Life:
Linking to Current Content
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In the 1800’s, Austrian monk Gregor Mendel discovered
how traits (the physical things you can see on the outside
of an organism) are passed on from parent to offspring.
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The information Mendel lacked was what these traits were
transported in or on.
◦ Physically, how did the trait exist in an organism?
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We now know that traits
are transferred from
parents to offspring
through the transfer and
sharing of genes
contained in DNA.
But it took 50 years of
research in studies
performed by important
scientists.
DNA: The
Genetic Material
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Today you are going to learn all about the basic
structure of the molecule that holds our
heredity… DNA.
By the end of this lesson you will be able to…
◦ Identify the substance that makes up genetic material.
◦ Name the experiments that identified the role of DNA as
the genetic material.
◦ Name the studies that led to the discovery of DNA’s
structure.
◦ Relate the structure of DNA to the function of DNA as a
carrier of information.
◦ Build a model of a DNA molecule.
Objectives: DNA Structure
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Gene
DNA
Nucleotide
Purine
Pyrimidine
Vocabulary
Part I: DNA History
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So, Mendel knew what happens with traits but
not how they were stored and transferred.
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Traits are contained as directions in DNA
(deoxyribonucleic acid): the primary genetic
material that contains genes.
◦ It causes recognizable, inheritable characteristics in
related groups of organisms.
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Traits are “written” into specific areas, called
genes, within the large, continuous DNA
molecules called chromosomes.
A gene is the most basic physical unit of
heredity
◦ A gene contains the instructions for to make a trait, just
like a recipe contains the instructions for a meal.
DNA, the Genetic Material
Searching for the Genetic Material
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Three major experiments led to the
conclusion that DNA is the genetic
material in cells.
These experiments were performed by:
Discovering DNA as the genetic material
Scientist (s)
Griffith
Avery
Hershey and Chase
Contribution
Searching for the Genetic Material
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Griffith worked with two related strains of bacteria which cause
pneumonia in mice.
◦ One strain was deadly… it made the mice sick and killed them.
◦ The other strain did little to nothing to the mice.
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Griffith discovered that when harmless live bacteria were
mixed with heat-killed disease-causing bacteria and then
injected into mice, the mice died.
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These results led Griffith to discover transformation.
Transformation is a change in genotype that is caused when
cells take up foreign genetic material.
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Griffith’s experiments led to the conclusion that genetic
material could be transferred between cells.
Griffith’s Discovery of Transformation
Harmless
bacteria
Deadly
bacteria
Deadly bacteria that
was made harmless
because it was boiled
to death.
Harmless bacteria
mixed with killed deadly
bacteria…
Conclusion… Whatever made the deadly bacteria deadly was being
transferred into the harmless bacteria. This process of exchanging information
between organisms is called TRANSFORMATION…
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So first, genetic material is known to
exist and it can be transferred in a
process called transformation.
Searching for the Genetic Material
Griffith proved hereditary information can
be transferred but what was it?
 Avery wanted to determine whether the
transforming agent in Griffith’s
experiments was protein, RNA, or DNA.
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Avery used enzymes to destroy each of
these molecules in heat-killed bacteria.
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Avery’s experiments led to the conclusion
that DNA is responsible for transformation
in bacteria.
So first genetic material is known to
exist and it can be transferred in a
process called transformation.
 Then we knew that DNA was the
genetic material being passed
on…but was it the only genetic
material?
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Searching for the Genetic Material
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Hershey and Chase studied
bacteriophages.
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Bacteriophages are viruses that infects
bacteria.
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By using radioactive isotopes (chemical
that emit light when charged with UV
radiation) painted in the virus’s DNA and
proteins, Hershey and Chase showed that
DNA, not protein, is the genetic material
in viruses.
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– Griffith
So first genetic material was known to exist
and it can be transferred.
– Avery
Then we knew that DNA was the genetic
material being passed on…but was it the
only genetic material?
– Hershey & Chase
Next a discovery lead to the realization that
DNA, not anything else, was responsible for
containing the genetic information that is
passed between organisms.
The next question…What is the structure?...
Discovering DNA’s Structure
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The search for DNA’s structure was
headed by several scientists that each
contributed a little at a time:
Discovering DNA Structure
Scientist (s)
Watson & Crick
Chargaff
Franklin & Wilkins
Contribution
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The discovery of the structure of DNA
was credited to Watson & Crick
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but they borrowed information from several
other scientists.
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Chargaff:
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Franklin and Wilkins:
◦ Showed that the amount of adenine always equaled the
amount of thymine
◦ & the amount of guanine always equaled the amount of
cytosine.
◦ Developed X-ray diffraction images of strands of DNA
that suggested the DNA molecule resembled a tightly
coiled helix.
Discovering DNA’s Structure
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Watson and Crick used both Chargaff’s data and
the X-ray diffraction studies to create a complete
three-dimensional model of DNA.
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Their model showed a “spiral staircase” in which
two strands of nucleotides twisted around a
central axis.
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These pictures are looking straight down the
staircase.
Discovering DNA’s Structure,
continued
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What were the three experiments that
lead to the discovering what the genetic
material in humans was?
 What is the name of the molecule that
contains genetic information?
 Who is credited for discovering the
structure of DNA?
 Name two other contributing scientists
and what they discovered.
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Concept Check:
Part II: DNA Structure
DNA is often
compared to a
ladder or a spiral
staircase. Look at
picture to the
right and answer
the following
questions.
How is the structure of DNA similar to that of a
ladder or spiral staircase?
How is it different from that of a ladder or spiral
staircase?
The Shape of DNA
The spiral shape of DNA is known
as a double helix.
 Double
= two strands
 Helix
= spiraled around itself.
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The Structure of DNA
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DNA is made up of
individual nucleotides
bonded to each other.
The Structure of DNA
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A nucleotide is a DNA subunit made up of three
parts: a phosphate group, a 5-carbon sugar
group, and a nitrogen-containing base.
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The five-carbon
sugar in DNA is
called deoxyribose,
from which DNA
gets its full name,
deoxyribonucleic
acid.
◦ “de” means removed =
it lacks one hydroxide
group present in RNA
The Shape of
DNA
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The blue ribbon area is known as
the BACKBONE
◦ These are always the same.
◦ PhosphateRibosePhosphateRibose
Phosphate…
P
P
P
P
R
R
R
R
Phosphate
Deoxyribose
Phosphate
DNA Backbone
The Shape of DNA
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The two strands are antiparallel.
The backbones are equidistant but
going in opposite directions.
The Structure of DNA
The term “anti-parallel” refers to the fact that
whereas DNA backbones are equidistant from each
other, they go in opposite directions.
 One strand goes in the 3’5’ direction
 The other goes in the 5”  3’ direction
 The 3’ or 5’ refers the carbons in the ribose sugar.
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C#5
C#4
Ribose
C#3
Anti-Parallel
Carbon#1
C#2
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Ribose is a 5carbon sugar.
5’ refers to the
end of the
nucleotide
closest to the
#5 carbon.
3’ refers to the
end of the
nucleotide
closest to the
#3 carbon.
The Shape of
DNA
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The two strands are
complimentary.
One strand contains
bases that are
complimentary to the
other strand’s bases.
Compliments… not mirror images
• DNA is held together by hydrogen bonds.
• They are represented by dashed lines.
• Notice the # of H-bonds. They change depending
on the bases involved.
DNA: Hydrogen Bonding
The Bases
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The four kinds of bases are adenine (A), guanine
(G), thymine (T), and cytosine (C).
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Bases A and G have a double-ring structure and
are classified as purines.
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Bases T and C have a single-ring structure and are
classified as pyrimidines.
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A purine on one strand of a DNA molecule is always
paired with a pyrimidine on the other strand.
Specifically, adenine always pairs with thymine,
and guanine always pairs with cytosine.
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Base-pairing rules (as given to us by
Chargaff) are dictated by the chemical
structure of the bases.
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It has to do with the category
(purine/pyrimidine) as well as their hydrogen
bonding characteristics.
◦ A double bonds with T
◦ G triple bonds with C
◦ The bonds are HYDROGEN BONDS
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Whereas hydrogen bonds are weak
individually, the billions of bonds between
bases keep the two long strands of DNA
together.
Base-Pairing
The “puzzle piece”
refers to the
hydrogen bonding
between the
paired bases.
Guanine and
cytosine have 3
hydrogen bonds
Complimentary Bases
whereas thymine
and adenine have
2 hydrogen bonds.
How The Bases Fit Into Larger
Molecules
What to Know at This Point
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The three experiments that lead to the discovery of
DNA as the genetic material.
Who contributed to the discovery of the structure
of DNA?
The structure of DNA
◦ What a nucleotide is composed of.
◦ How the nucleotides are arranged to create strands of
DNA.
◦ What holds the bases together…Hydrogen Bonds (Hbonds)
◦ The base-paring rules
 A – T, C – G, pyrimidine, purine.
 How many hydrogen bonds between the bases
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HW: Complete the half-sheet. Fill in all shapes with
abbreviations for the part that goes there. Label
the hydrogen bonds too.
Summary: Complete the Illustration in
your notes.
Using the rules of complementary bases and h-bonding,
determine what each shape is.
To solve:
Look at the number of rings then the number of bonds…
Nitrogenous base
Tyrosine
Ribose
Phosphate
Phosphate
Ribose
Ribose
Phosphate
Phosphate
Nitrogenous base
Cytosine
Ribose
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Take out your homework
◦ The half sheet you had from yesterday.
We’ll discuss in 5 minutes.
 Make sure you check with neighbors and
get clarification on anything you couldn’t
get.
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Day 2
The Information in DNA
The information in DNA is contained in the
order of the bases.
 The order of how the bases are arranged
determines the trait that will result.
 This order is called the “sequence”
 Different sequences, called “spellings”, give
different genes.
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◦ AATGCTAGC would be spelling of one the
sequence in one gene
◦ TGCATACCG would be part of another
◦ It’s the same stuff, just a different arrangement
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Paired bases on opposite sides of a double helix are said to
be complementary because they fit together like puzzle
pieces.
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Because of base-pairing rules, if the sequence (the order)
of bases is known for one strand of DNA, then the
sequence of bases for the complementary strand (the
other) can be quickly identified or predicted.
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Ex. CTGAA BONDS WITH…. This is the TEMPLATE strand
GACTT
This is the COMPLEMENTARY strand
What is the complementary strand for.
◦ CCGTATACCGATTG? (Template Strand)
◦ GGCATATGGCTAAC (Complimentary Strand)
The Information in DNA
Pick up an
assignment sheet
from the back.
 This is HOMEWORK
and is due by
tomorrow.
 Scissors and tape
are up front.
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Homework
Check in when complete.
It’s due tomorrow if not.

DNA is the primary material that causes inheritable
characteristics in related groups of organisms.

Three major experiments led to the conclusion that DNA is the
genetic material in cells. These experiments were performed
by Griffith, Avery, and Hershey and Chase.

A DNA molecule is shaped like a spiral staircase and is
composed of two parallel strands of linked subunits.
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The information in DNA is contained in the order of the bases,
while the base-pairing structure allows the information to be
copied.
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Watson and Crick used information from experiments by
Chargaff, Wilkins, and Franklin to determine the threedimensional structure of DNA.
Summary
Nitrogenous Bases: Categories,
pairing
Base
Number
of rings
Makes it a
Hydrogen Structure
bonds with
Adenine
2
Purine
Thymine
Guanine
2
Purine
Cytosine
Thymine
1
Pyrimidine
Adenine
Cytosine
1
Pyrimidine
Guanine