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DNA
"The Blueprint of Life“
Discovery the DNA is the Genetic
Material for a Cell
1831 Swiss biochemist Friedrich Miescher
* Discovered a microscopic substance in the pus of discarded
surgical bandages (residue from the nuclei of cells).
* Miescher called the substance “nuclein”. (We now call this
DNA)
1919 Phoebus Levene identified the base, sugar and phosphate
nucleotide unit. Levene suggested that DNA consisted of a string
of nucleotide units linked together through the phosphate groups.
However, Levene thought the chain was short and the bases
repeated in a fixed order.
1937 William Astbury produced the first x-ray diffraction patterns
that showed that DNA had a regular structure.
Who was awarded the Nobel Prize in Physiology
for determining the exact composition of nuclein?
1910Albrecht Kossel
* In one of his first experiments, he boiled
nuclein and determined that it contained
phosphorus and hypoxanthine (a breakdown
product of nucleoproteins).
* In later investigations, he found the bases
adenine, guanine, and thymine.
Frederick Griffith (1928)
Showed that nonlethal bacteria could be transformed into lethal
bacteria.
Bacteria = Streptococcus pneumonia
S strain = causes pneumonia
R strain = harmless
Experiment 1:
injected mice with live R cells (harmless)
a. mice lived
Experiment 2:
Injected mice with live S cells (harmful)
a. mice died
Experiment 3:
Injected mice with heat killed S cells (harmful but dead)
a. mice lived
Experiment 4:
Injected mice with mixed (living R –harmless mixed with dead harmful S)
a. mice died
Frederick Griffith
Final conclusions: Some material must have been
transferred from the heat-killed S (harmful) into
the live R (harmless) bacteria.
Transforming Principle: The mystery material that
could change the harmless bacteria into harmful
bacteria.
Oswald Avery 1944
Purpose for the combination: to determine exactly what
the transforming principle was.
Purification purpose: It allowed them to directly observe
the transformation from R (harmless) into S (harmful)
(They wanted to see if the transforming principle was
DNA or proteins)
Conclusion: DNA is the transforming principle (genetic
material) In other words…. The material basis for a
gene is DNA
Following the Work of Griffith
Colin M. MacLeod and Maclyn McCarty
1. Published a paper in 1944
2. Followed the work of Griffith in order to
discover what causes nonlethal bacteria to
transform to a lethal strain.
3. Used special enzymes to determine that, in
fact, DNA is the transforming factor.
Hershey and Chase (1952)
Did Hershey and Chase provide conclusive evidence that showed
DNA to be the transforming/genetic material? YES
Why a virus?
* A virus contains two parts: Genetic material (DNA) and a
protein coat.
* Bacteriophages were big (for a virus) and will not harm a
human
who was studying it. “Phage” only attacks bacteria.
Conclusion:
DNA is the only part of the phage that entered into the bacteria,
therefore DNA is the genetic material/transforming factor.
(Further proved that Avery’s team was correct)
Why were the 1950’s such an
important era for DNA research?
1. In the wake of World War II, when research was
primarily driven by wartime need, researchers
returned to basic rather than applied research.
2. The 1950’s was a period of intense study as
scientists attempted to understand the nature of
DNA and the gene.
3. The structure of DNA was attacked from both
biochemical and structural aspects.
The Race for the Double Helix
1950’s
Researchers
Chargaff (1950)
The race for DNA’s structure begins
Chargaff studied the base composition of DNA from
various organisms.
Chargaff’s findings:
1. There were 4 bases in DNA (Adenine = A, Thymine = T, Cytosine = C
and Guanine = G) found in all living things, but the proportion of the four
bases differs.
Which bases are equal:
Adenine is equal with Thymine
Cytosine is equal with Guanine
“Chargaff’s Rule”
Base Pairing Rules
A=T
C=G
Franklin and Wilkins (1951)
Technique called: X-Ray Crystallography (X-ray picture
of DNA)
Suggestions:
The image showed an “X” shape surrounded by a circle.
This suggested that DNA is in the shape of a double
helix (twisted ladder) that consist of 2 strands (sides)
that are a regular, consistent width apart.
Maurice Wilkins (male)won a Nobel prize (1962) for
this discovery. Rosalind Franklin (female) did not.
She died of cancer before the prize was awarded.
Watson and Crick (1953)
Backbone of DNA: (sides)
* Phosphate group covalently bonded to a deoxyribose sugar
group. (P-S)
Middle of DNA:
* Nitrogen bases (A, T, C or G)
Overall Shape:
* Double Helix
Both Watson and Crick along with Wilkins won the Nobel Prize
in 1962 for their discovery.
Francis Crick passed away on July 28, 2004
James Watson is still living. He was born April 6, 1928… that
makes him 84-85 years old!
A lot has happened since 1866 when Mendel worked with his pea
plants.
DNA stands for...
DeoxyriboNucleic Acid
Location for Chromosomes
The chromosomes are located in the nucleus of a
eukaryotic cell.
DNA can be found in the:
Nucleus of a cell
Mitochondria of a cell
Chloroplast of plant cells
Structure of DNA
1.
2.
Credit for the structure of DNA is
given to James Watson and
Francis Crick.
DNA’s shape was determined to
be a double helix.
Sides of DNA
1. The sides of DNA are
made up of:
a. Phosphate group
bonded to a Dexoyribose
Sugar.
2. The sides are held
together by covalent
bonds. (strong bonds)
Middle of DNA
1. The middle of DNA is
composed of:
a. Nitrogen bases
(Adenine, Cytosine,
Thymine or Guanine).
2. The middle bases are
held together by
hydrogen bonds. (easy
to break)
Sugar Found In DNA
Deoxyribose Sugar
Base Bonding
Adenine bonds with Thymine
Guanine bonds with Cytosine
Nucleotides
1. DNA is made up of
repeating units called:
Nucleotides
2. 3 parts of a nucleotide:
a. Phosphate group
b. Deoxyribose sugar group
c. Nitrogen base
Review
http://www.youtube.com/watch?v=qy8dk5iS1f0
Function
Codes for proteins that create your genes (traits)
Structure
made of repeating subunits called nucleotides
Bonding
1. The sides of the DNA ladder are
a. Phosphate & sugar
2. Held together by Covalent bonds
3. In the middle are the bases.
a. held together by hydrogen
bonds.
Base Pairing Rules
Adenine <==> Thymine
Guanine <==> Cytosine
Base Pair Rule Practice
One side:
Other side:
A T A
T C A
T G C
G G G
Let's Review What We Know About DNA
1. DNA stands for: De _____ ribo ______ acid
2. What is the shape of DNA? _______________
3. Who established the structure of DNA? ____________
4. Adenine always pairs with _______________
5. The sides of the DNA ladder are deoxyribose and _____
6. Guanine always pairs with _____________
7. What is the complimentary sequence: A A T G C A
8. The two sides of DNA are held together by _______
bonds.
9. DNA is composed of repeating subunits called
______________________
10. What are the 4 bases that make up the rungs of the DNA
ladder? _______________________________________
Review of History of DNA
Griffith, Avery, Hershey-Chase, WatsonCrick, Wilkins-Franklin, Chargaff
1. Which group worked with viruses?
2. What does “Chargaff’s Rules” state?
3. X-ray diffraction photographs by Wilkins and
Franklin suggested that DNA have what shape?
4. Which scientist worked with bacteria and said
that something “transformed” the harmless into
harmful bacteria?
5. Which scientists also worked with bacteria and
said that DNA was the “transforming” factor?
DNA Replication (DNA  DNA)
1. DNA is located in the nucleus.
2. DNA replication occurs in the nucleus.
3. DNA replication occurs during the S phase of
Interphase in mitosis/meiosis.
4. DNA needs to replicate in order to assure that
each cell has a complete set of identical genetic
information.
5. Steps to DNA replication are on page 237 in HBT.
Replication
• DNA is semiconservative because each molecule
(new DNA molecule) contains an original strand
and one new strand.
• Enzymes
– Helicase: “unwinds” the helix
– DNA polymerase: bond the new nucleotides together
– Ligase: “proof-reads” the final product to check for
errors
Replication Review
Replication takes place where in the cell?
During which part of the cell cycle does replication
occur?
What does replication make? DNA 
RNA
Central Dogma:
Information flows in one direction
From DNA to RNA
Consist of three processes
1. Replication: DNA  DNA
2. Transcription: DNA  RNA (m-RNA)
3. Translation: protein synthesis
Types of RNA
A. Messenger RNA: (m-RNA)
•
•
Intermediate message that is translated to form a protein.
Assembled in the nucleus during transcription; a single
strand copied from original DNA strand (T replaced with U)
Codes for the amino acids.
B. Transfer RNA: (t-RNA)
1.
Found in the cytoplasm; bonds at a ribosome; anticodon on
one end bonds with matching mRNA codon during
translation. Carries the amino acid to the mRNA in order to
form the protein.
C. Ribosomal RNA: (r-RNA)
1. Helps in the creation of the structure of a ribosome.
RNA carries the
"message" to the
ribosomes, where
proteins are made
Central Dogma of Protein Formation
DNA --> RNA --> Protein
(nucleus)
(ribosomes)
Proteins are the building
blocks of the organism (traits)
Transcription
Transcription - process where RNA is made
from DNA
DNA  RNA
(DNA  mRNA)
Begins = _____ Ends at = _____
Reading a Codon Chart
If DNA has the code: TAC GGG ATT
What would the mRNA code be:
What amino acids would this code for?
Transcription Review
Transcription
DNA 
Where does it occur?
begins:
ends:
The mRNA is called the codon
Translation/ Protein Synthesis
• Translation - process where proteins are
made from RNA
Protein Synthesis
Takes place = _________
Uses tRNA which is called the anticodon