Welcome 1/11/16 – 1/15/16
 Warm up #6-10
 Vocab #12 I’ll hand it out on Friday.
 Turn in Cornell Notes
 Notes on the history of DNA, Components of DNA
 Check for understanding questions
 Assign DNA Project
 Homefun: None! so that you can work on DNA project
immediately! Or Finishing the cell cycle paper that is
due this Friday!
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History of DNA
 Early scientists thought protein was the cell’s
hereditary material because it was more
complex than DNA
 Proteins were composed of 20 different amino
acids in long polypeptide chains
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Transformation
 Fred Griffith worked with virulent S and
nonvirulent R strain Pneumoccocus bacteria
 He found that R strain could become virulent
when it took in DNA from heat-killed S strain
 Study suggested that DNA was probably the
genetic material
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Griffith’s Experiments
S strain:
R strain: S strain: Mixture:
causes disease harmless heat killed R, dead S
Mouse dies Mouse
of pneumonia. lives.
Mouse Mouse dies
Live S strain
lives. of pneumonia.
Griffith Experiment
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History of DNA
 Chromosomes are made of both
DNA and protein
 Experiments on bacteriophage
viruses by Hershey & Chase
proved that DNA was the cell’s
genetic material
Radioactive
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32P
was injected into bacteria!
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Bacterial Viruses
Bacteriophage: a kind of virus that infects bacteria
DNA
head
tail sheath
tail fiber
Hershey-Chase Experiment
Bacteriophage with
radioactive tag in
DNA
Phage
infects
Radioactivity
inside bacterium
bacterium.
Bacteriophage with
radioactive tag in
protein coat
Phage infects
bacterium.
No radioactivity
inside bacterium
Discovery of DNA
Structure
 Erwin Chargaff showed the amounts of the four
bases on DNA ( A,T,C,G)
 In a body or somatic cell:
A = 30.3%
T = 30.3%
G = 19.5%
C = 19.9%
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Chargaff’s Rule
[A] = [T] and [C] = [G]
Chargaff’s Rule
 Adenine must pair with Thymine
 Guanine must pair with Cytosine
 The bases form weak hydrogen bonds
T
A
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G
C
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DNA Structure
 Rosalind Franklin took
diffraction x-ray photographs
of DNA crystals
 In the 1950’s, Watson & Crick
built the first model of DNA
using Franklin’s x-rays
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Franklin’s X-rays
• DNA is a helix.
• Likely two strands to the molecule
• Nitrogenous bases near the center of the molecule
The Work of Watson and Crick
DNA is a double helix, in which two strands of nucleotide
sequences are wound around each other.
The Double Helix: Antiparallel Strands
The two strands in a DNA molecule run in opposite
directions.
Check for understanding
Before, why did scientists thought protein was the cell’s
hereditary material?
2. Name the scientists and their experiments that rejected the
notion that protein was the cell’s hereditary material. And
what is indeed the cell’s hereditary materials?
3. What is Chargaff’s rule?
4. How did DNA model first constructed?
1.
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The Role of DNA: Storing Information
The genetic material stores information needed by every
living cell.
The Role of DNA: Copying and Transmitting
Copying
Information
Transmitting
Information
The Role of DNA: Summary
1. Store information
2. Copy information for daughter cells
3. Transmit information to daughter cells
DNA
 DNA is often called the
blueprint of life.
 In simple terms, DNA
contains the
instructions for making
proteins within the cell.
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Why do we study DNA?
We study DNA for many
reasons, e.g.,
 its central importance
to all life on Earth,
 medical benefits such
as cures for diseases,
 better food crops.
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Chromosomes and DNA
 Our genes are on
our chromosomes.
 Chromosomes are
made up of a
chemical called
DNA.
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The Shape of the Molecule
 DNA is a very long
polymer.
 The basic shape is like
a twisted ladder or
zipper.
 This is called a double
helix.
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The Double Helix Molecule
 The DNA
double helix
has two strands
twisted
together.
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One Strand of DNA
 The backbone of the
molecule is
alternating
phosphates and
deoxyribose sugar
 The teeth are
nitrogenous bases.
phosphate
deoxyribose
bases
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O
O -P O
O
O
O -P O
O
One deoxyribose together with
its phosphate and base make a
nucleotide.
O
O -P O
O
Nitrogenous
base
O
Phosphate
C
C
C
O Deoxyribose
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One Strand of DNA
nucleotide
 One strand of DNA is a
polymer of nucleotides.
 One strand of DNA has
many millions of
nucleotides.
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Four nitrogenous bases
DNA has four different bases:

Cytosine C
 Thymine T
 Adenine A
 Guanine G
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Two Kinds of Bases in DNA
 Pyrimidines are
single ring bases.
 Purines are double
ring bases.
N C
O C
N
C
N C
N
N C
C
C
N
N C
N C
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Thymine and Cytosine are
pyrimidines
 Thymine and cytosine each have one ring of
carbon and nitrogen atoms.
N
O
N
O
C
C C
N
N
C
C
thymine
O
C
C
C
N
C
cytosine
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Adenine and Guanine are purines
 Adenine and guanine each have two rings of
carbon and nitrogen atoms.
O
N
N
N
C
C
N
C
C
C
C
N
N
N
Adenine
N
C
N
C
Guanine
C
C
N
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Antiparallel Strands
 One strand of
DNA goes from
5’ to 3’ (sugars)
 The other
strand is
opposite in
direction going 3’
to 5’ (sugars)
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Two Stranded DNA
 Remember, DNA has two
strands that fit together
something like a zipper.
 Most DNA has a right-
hand twist with 10 base
pairs in a complete turn
 The teeth are the
nitrogenous bases but why
do they stick together?
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N
Hydrogen Bonds
C
N
N
O
C
C
 The bonds between cytosine
and guanine are shown here
with dotted lines
C
 Hydrogen bonds are weak but
there are millions and
millions of them in a single
molecule of DNA.
N
N
C
 The bases attract each other
because of hydrogen bonds.
N
C
N
C
C
C
O
N
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Hydrogen Bonds, cont.
 When making hydrogen
bonds, cytosine always
pairs up with guanine
 Adenine always pairs up
with thymine
N
O
O
C
C
C C
N
C
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DNA by the Numbers
 Each cell has about 2 m
of DNA.
 The average human has
75 trillion cells.
 The average human has
enough DNA to go from
the earth to the sun
more than 400 times.
 DNA has a diameter of
only 0.000000002 m.
The earth is 150 billion m
or 93 million miles from
the sun.
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Draw a model of
DNA double helix
with all of its
components label
How the Code Works
The combination of A,T,G,C determines what
traits you might have.....
C A T C A T = purple hair
T A C T A C = yellow hair
Think of the bases of DNA like letters.
Letters form words....
Words form sentences....
*endless
combinations
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 rings of the DNA
ladder? _______________________________________
Welcome 1/11/16 – 1/15/16
 Warm up #11-15
 Vocab #12
 Notes on DNA Continue
 Check for understanding questions
 Homefun: None, but make sure you work on your DNA
project
 Reminder: I’ll check “Check for understanding
question next Tuesday and Wednesday”
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Replication Facts
 DNA has to be copied
before a cell divides
 DNA is copied during the S
or synthesis phase of
interphase
 New cells will need identical
DNA strands
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Synthesis Phase (S phase)
 S phase during interphase of the
cell cycle
 Nucleus of eukaryotes
DNA replication takes
place in the S phase.
S
phase
G1
interphase
G2
Mitosis
-prophase
-metaphase
-anaphase
-telophase
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DNA REPLICATION
the process by which DNA makes a copy of
itself (cell division)
SEMI-CONSERVATIVE - half of the old strand is saved
Synthesis of the New DNA
Strands
 The Lagging Strand is synthesized
discontinuously against overall direction of
replication
 This strand is made in MANY short segments
It is replicated from the replication fork
toward the origin
Leading Strand
5
’
3’
DNA Polymerase
RNA Primer
5’
3’
Lagging Strand
3’
5’
3’
5’
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Lagging Strand Segments
 Okazaki Fragments - series of short
segments on the lagging strand
 Must be joined together by an enzyme
DNA
Polymerase
Okazaki Fragment
RNA
Primer
5’
3’
Lagging Strand
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3’
5’
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Joining of Okazaki Fragments
 The enzyme Ligase joins the Okazaki
fragments together to make one strand
DNA ligase
5’
3’
Okazaki Fragment 1
Lagging Strand
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Okazaki Fragment 2
3’
5’
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Replication of Strands
Replication
Fork
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Point of Origin
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Base Pair Rule
One side:
Other side:
A T A
T C A
T G C
G G G
Proofreading New DNA
 DNA polymerase initially makes about 1 in
10,000 base pairing errors
 Enzymes proofread and correct these
mistakes
 The new error rate for DNA that has been
proofread is 1 in 1 billion base pairing
errors
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Semiconservative Model of
Replication
 Idea presented by Watson & Crick
 The two strands of the parental
molecule separate, and each acts as a
template for a new complementary
strand
 New DNA consists of 1 PARENTAL
(original) and 1 NEW strand of DNA
DNA Template
Parental DNA
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New DNA
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DNA Damage & Repair
 Chemicals & ultraviolet radiation
damage the DNA in our body cells
 Cells must continuously repair
DAMAGED DNA
 Excision repair occurs when any of
over 50 repair enzymes remove
damaged parts of DNA
 DNA polymerase and DNA ligase
replace and bond the new nucleotides
together
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Question:
 What would be the
complementary DNA
strand for the following
DNA sequence?
DNA 5’-CGTATG-3’
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Answer:
DNA 5’-CGTATG-3’
DNA 3’-GCATAC-5’
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RNA - the messenger
*single strand
*ribose sugar
*contains no thymine, uracil instead
RNA carries the
"message" to the
ribosomes, where
proteins are made
Transcription - process where RNA is
made from DNA
Translation - process where proteins
are made from RNA
DNA --> RNA --> Protein
Proteins are the building
blocks of the organism (traits)
Transcription: DNA to RNA
DNA: A T A G C G
RNA:
1.
2.
3.
4.
Compare DNA vs. RNA
What is transcription?
Make up a sequence of DNA strand of 10 base
pairs, then use it to make an RNA strand
What is translation?
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