Chapter 12: DNA
Deoxyribonucleic Acid
Section 1:
The Discovery of DNA
Discovery of DNA
Scientist new that people
had different traits
because they had
different genes.
Scientist did not know what
type of molecule made
up our genes.
Frederick Griffith
• Studied bacteria that caused
pneumonia
• He figured out that you
could change one strain of
bacteria into another strain
of bacteria – transformation
Griffith’s Experiment
Two Strains of Bacteria
R strain - Harmless
S strain – Deadly
Discovery of DNA
Explain the results of Griffith’s experiment. Why
did mouse 4 die?
Discovery of DNA
Griffith’s Conclusion: “something”
transformed the harmless bacteria into
the deadly bacteria. (He called this
process transformation)
Oswald Avery – repeated Griffith’s work
to determine which molecule was
responsible for transformation
• Conclusion: DNA was the
transforming factor that caused the
change in the R-strain
Discovery of DNA
Alfred Hershey & Martha Chase
• Question: Are genes made of DNA or
proteins?
• What they know:
 viruses use other organisms to
reproduce
 Viruses only contain DNA and a
protein coat.
 Whichever virus particle enters the
cell must be the material that makes
up genes.
Discovery of DNA
Hershey and Chase
• Experiment:
– They tagged the virus DNA
with blue radioactive
phosphorous
– They tagged the protein coat
with red radioactive sulfur
• Results:
– the cells only contained blue
radioactive phosphorous.
• Conclusion:
– Virus only injects DNA
(confirms Avery’s results)
Section 2: Structure of DNA
Function: Stores and transmits genetic information.
Structure:
• Type of organic macromolecule = nucleic acid
• Polymer = polynucleotide
• Monomer = nucleotide
–
Each nucleotide contains 3 parts:
1. Sugar (deoxyribose)
2. Phosphate group
3. Nitogen-containing base
Structure of DNA
DNA has 4 different nitrogenous bases
What is the structural difference between purine and
pyrimidine bases.
Chargaff
• Analyzed the percentage of each
base in a strand of DNA.
• His results:
– The amount of adenine is equal
to the amount of thymine
– Cytosine is equal to guanine
– Why did he get these results?
Structure of DNA
Base Pairing
• Adenine (A) always bonds with Thymine (T)
• Guanine (G) always bond with Cytosine (C)
Hydrogen Bonding
• What is a hydrogen bond?
• Hydrogen bonds hold the two
strands of the DNA molecule
together
• There are 3 bonds between C and G
• There are 2 bonds between A and T
Structure of DNA
• Rosalind Franklin
– Took pictures of DNA
using x-rays.
– First person to determine
that the shape of a DNA
molecule was a double
helix.
Structure of DNA
James Watson and Francis Crick
• Built the first correct model of
a DNA molecule.
• What they learned . . .
– DNA is made of two
strands.
– Each strand has a sugarphosphate backbone.
– The bases are in the middle
Structure of DNA
• The strands are antiparallel
– They run in opposite directions.
– One strand is arranged 5’ to 3’
while the other strand is 3’ to 5’
– 5’ and 3’ refer to the carbon
atoms in the deoxyribose sugar.
Section 3:
DNA Replication
•
How does the structure of
DNA allow it to store
information?
•
How does the structure of
DNA allow it to
replicate?replicate?
DNA Replication
DNA Replication
How does it replicate?
1. Helicase: an enzyme that separates the 2 DNA
strands by breaking the hydrogen bonds.
– Nucleotides are added according to base pairing
rules, using DNA polymerase.
• DNA polymerase only move in one direction,
from 5’ to 3’.
DNA Replication
2. DNA Polymerase: adds nucleotides to the single
stranded DNA according to base pairing rules.
• DNA polymerase only move in one direction,
from 5’ to 3’.
DNA Replication
• Leading Strand: the 5’ to 3’ strand, polymerase can add
nucleotides to make one continuous strand.
• Lagging Strand: the 3’ to 5’ strand, polymerase moves in
the opposite direction.
– Polymerase forms short segments of DNA called
Okazaki fragments.
DNA Replication
3. Ligase: connects together the Okazaki fragments in
the lagging strand.
Chapter 12 Practice Quiz
Name the 3 parts that make up a DNA
nucleotide.
Which number represents a molecule of
deoxyribose?
Which numbers represent the parts of the
nucleotide that make up the backbone of
a DNA molecule?
Which number represents that part of the
nucleotide that can be found in the
center of a DNA molecule?
If DNA sequence is compose of 15%
adenine; how much thymine, guanine,
cytosine is in the DNA?
Chapter 12 Practice Quiz
Write the complementary sequence for the
DNA molecule from top to bottom.
What type of bond forms between two
complimentary bases in a double
stranded DNA molecule.
Which end of the DNA molecule is the 5’
end (Top or Bottom)?
How many nucleotides are shown in the
diagram?
Adenine and Guanine considered purine
bases. How is the structure of purine
different than pyrimidine's.
Chapter 12 Practice Quiz
9. Adds DNA nucleotides
during replication.
10. Connects together the
Okazaki fragments.
11. Separates the double helix
during replication.
12. The strand of DNA that
runs 5’ to 3’ and can be
made continuously.
a. Helicase
b. Ligase
c. DNA
Polymerase
d. Leading
Strand
e. Lagging
Strand
DNA Replication
Telomeres: The DNA found at the ends of the
chromosome.
– The DNA at the end of the chromosome is
difficult to replicate
– Telomerase adds short repeating segments of
DNA to the chromosome