Agenda March 8th Part I
• Turn in 3 HW Handouts on Scientific
Method
• Quiz # 1
• Video: The Double Helix
• Notes: DNA Structure, DNA Scientists
• Lab # 10: Extracting DNA
• Break
• In Class Reading and Questions:
– The Structure of DNA: Cooperation and
Competition
1
2
3
Review: What is DNA?
• DNA is a molecule that
contains ALL of an
organism’s genetic
material and is
therefore responsible
for HEREDITY
• A strand of DNA
contains many GENES
all of which code for
PROTEINS
• Each of these proteins
has a different function
in a cell
Two scientists,
James Watson and
Francis Crick, were
the first to discover
the structure of DNA
They referred to it as a DOUBLE HELIX
because it contains two complementary
strands, each of which is shaped like a spiral
staircase
DNA stands for
Deoxyribonucleic
Acid
DNA is made up of 3 main
components:
Deoxyribose – a sugar
molecule
Phosphates – which make
up part of the backbone
Nitrogenous bases –
Thymine, Adenine,
Guanine, Cytosine
DNA
Structure
8
DNA
• Two strands coiled called
a double helix
• Sides made of a pentose
sugar Deoxyribose bonded
to phosphate (PO4) groups
by phosphodiester bonds
• Center made of nitrogen
bases bonded together by
weak hydrogen bonds
9
DNA Double Helix
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone
10
Helix
• Most DNA has a right-hand
twist with 10 base pairs in a
complete turn
• Left twisted DNA is called
Z-DNA or southpaw DNA
• Hot spots occur where right
and left twisted DNA meet
producing mutations
11
DNA
• Stands for
Deoxyribonucleic acid
• Made up of subunits
called nucleotides
• Nucleotide made of:
1. Phosphate group
2. 5-carbon sugar
3. Nitrogenous base
12
DNA Nucleotide
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C1
C4
Sugar
(deoxyribose)
C3
C2
Nitrogenous base
(A, G, C, or T)
13
Pentose Sugar
• Carbons are numbered clockwise
1’ to 5’
5
CH2
O
C1
C4
Sugar
(deoxyribose)
C3
C2
14
5
DNA
O
3
3
P
5
O
O
C
G
1
P
5
3
2
4
4
P
5
P
2
3
1
O
T
A
3
O
3
5
O
5
P
P
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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)
16
Nitrogenous Bases
• Double ring PURINES
Adenine (A)
Guanine (G)
A or G
• Single ring PYRIMIDINES
Thymine (T)
Cytosine (C)
T or C
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Base-Pairings
• Purines only pair with
Pyrimidines
• Three hydrogen bonds
required to bond Guanine
& Cytosine
3 H-bonds
G
C
18
•Two hydrogen bonds are
required to bond Adenine &
Thymine
T
A
19
Question:
• If there is 30%
Adenine, how much
Cytosine is present?
20
Answer:
• There would be 20%
Cytosine
• Adenine (30%) = Thymine
(30%)
• Guanine (20%) = Cytosine
(20%)
• Therefore, 60% A-T and
40% C-G
21
Lab 10
DNA extraction from bananas !!!
22
Banana DNA Lab
• Purpose: to extract DNA from the fruit
of a bananas…
23
Lab Objectives
• Follow steps for extracting DNA from
plant cells
• Observe DNA (Yes, you can actually
see DNA) !!!
Banana DNA Lab
• Follow procedure on the handout
• Complete pages 95-99
25
Lab Steps
•
•
•
•
•
•
Read the directions !!!
Squish the fruit to a slush in the baggie
Mix in detergent solution
Filter extract through a coffee filter
Layer cold alcohol over the extract
Repeat steps for the banana
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Lab Closure
Know the reason for each of these steps !
• Why do you squish the fruit to a slush ?
• Why do you mix in detergent solution
• Why filter extract through a coffee filter ?
• Why layer cold alcohol over the extract ?
27
Match these steps
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Review Questions
1. In what part of the cell is DNA found ?
2. What are the units (building blocks) of
DNA called ?
3. Those units are made up of what 3 parts
?
4. What are the names of the 4 bases ?
5. How do the bases pair up in a DNA molecule ?
What are the complementary bases to this
DNA strand: TTACCTGCAGGC
6. How does DNA impact our lives ?
Answers
1. DNA is found in the nucleus
2. The units (building blocks) of DNA are
called nucleotides
3. Those units are made up of these 3
parts: sugar, phosphate, base
4. The names of the 4 bases are adenine,
guanine, cytosine, thymine
5. A pairs with T and G pairs with C
6. TTACCTGCAGGC pairs with
AATGGACGTCCG
What are some common uses
of DNA technology today ?
• DNA evidence from crime scenes
(forensics)
• Genetic engineering of plants, animals
• Cloning of research animals
• Genetic screening of individuals for
hereditary diseases
• Paternity tests
•Dog Poop Tests !!!!
31
Testing Dog Poop DNA
• DNA testing can identify dogs through the
poop they leave behind…
• This is bad news for those who don’t clean
up after their pets…They face some pretty
stiff fines !!!
32
Objectives
To create a timeline of scientists who
have been important in the discovery of
DNA as the molecule of heredity
– List scientists and their contributions…
– Explain how the discovery of DNA
structure was both an example of
cooperation and an example of
competition
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DNA Scientists…
• Fredrich Miescher
• Frederick Griffith
• Oswald Avery, Colin Macleod,
Maclyn McCarty
• Erwin Chargaff
• Alfred Hershey and Martha Chase
• Rosalind Franklin and Maurice
Wilkins
• Linus Pauling
• James Watson and Francis Crick34
Timeline of
Discoveries:
The Search for DNA
35
Early DNA Scientists
36
37
38
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
39
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
40
Griffith Experiment
(1928)
41
Avery Experiment
(1943)
42
Avery Experiment
43
Erwin Chargaff (1950)
44
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%
45
Erwin Chargaff
46
Chargaff’s Rule
• Adenine must pair with
Thymine
• Guanine must pair with
Cytosine
• The bases form weak
hydrogen bonds
T
A
G
C
47
Hershey and Chase
(1952)
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Hershey and Chase
49
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 32P and 32s were injected into
bacteria. DNA has p (phosphorus) but not s
(sulfur). The 32P showed up in the bacteria
50
Rosalind Franklin (1953)
51
Rosalind Franklin
52
Rosalind Franklin
copyright cmassengale
53
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
54
Watson and Crick
(1953)
55
Linus Pauling: DNA as
a Triple Helix ???
copyright cmassengale
56
Watson and Crick
57
Don’t Forget Frederick
Sanger 1975
Sequencing of DNA
Bases
58
Structure of DNA Reading, Questions
1. What were the four initial clues that
gave insight into the importance and
structure of DNA?
2. What are the 3 basic components of
DNA ?
3. What are the 4 different DNA bases ?
4. How does this article show that
science relies on communication
within a diverse scientific community
?
59
Structure of DNA Reading, Questions
5. What technology came available in the
first half of the 20th century that made
solving the structure of DNA possible
? How did it help ?
6. Compare the approaches of Wilkins
and Franklin and the approaches of
Watson and Crick in solving DNA’s
structure
60
Structure of DNA Reading,
Questions
7. What was image “B51”? Who took it
?How did it help solve the puzzle of
DNA’s structure ?
8. How do the bases pair in DNA? How
does this agree with the previous
mysterious base ratios ?
9. How is reporting one’s findings and
sharing ideas essential for scientific
progress ? How did it make solving
61
the structure of DNA possible ?
Agenda March 8th Part II
•
•
•
•
•
Notes: DNA Replication
Notes: Proteins, Protein Structure
Lab # 5: Biomolecules II
Break
Protein Synthesis Video
• In Class Reading and Questions:
– Molecular Level of Genetics
• Video: One Wrong Letter
• Review for Exam I (Lectures 1,2,3,4)
62
DNA
Replication
63
Essential Question
• Think !!! How does the
structure of a double helix
ensure that all cells of an
organism get the same
genetic code ???
Lesson Objectives
1. Explain how DNA is
replicated (copied)
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
66
Synthesis Phase (S phase)
• S phase during interphase of the
cell cycle
• Nucleus of eukaryotes
S
DNA replication takes
place in the S phase.
phase
G1
interphase
G2
Mitosis
-prophase
-metaphase
-anaphase
-telophase
67
DNADNADNADNADNADNA
Replication Notes
DeoxyriboNucleic Acid
REPLICATION
VOCABULARY
•
•
•
•
•
•
•
•
Double Helix
Hydrogen Bonds
Sugar-Phosphate Backbone
Complementary
Template
Replication
DNA Polymerase
Helicase
DeoxyriboNucleic Acid
REPLICATION
• Replication is the duplication
of DNA that occurs in the S
Phase of Cell Cycle
• The two strands of DNA
separate and each acts as a
template for the formation of
a new strand.
Copying DNA
• Matching bases allows
DNA to be easily copied
Making new DNA
• Copying DNA
– replication
– DNA starts as a double-stranded
molecule
• matching bases (A:T, C:G)
– then it unzips…
DNA replication
• Strands “unzip” at the weak bonds
between bases
Enzyme: Helicase breaks
the hydrogen bonds
DNA replication
DNA bases
in nucleus
• Enzyme
DNA
polymerase
– DNA polymerase
– adds new bases
Copying
DNA
• Build daughter DNA
strand
– use original parent strand as
“template”
– add new matching bases
– synthesis enzyme =
DNA polymerase
DNA
Polymerase
New copies of DNA
• Get 2 exact copies of DNA to split
between new cells
DNA
polymerase
DNA
polymerase
Copied & Paired Up
Chromosomes
DeoxyriboNucleic Acid
REPLICATION
• There is only a 1 in a million chance
that there will be an error
– If there is an error it is called a
mutation (change in DNA)
• The cell proofreads the DNA and
repairs any mutations it might find
– So after this process a chance of
mutation is 1 in a billion
Question:
• What would be the
complementary DNA
strand for the following
DNA sequence?
DNA 5’-CGTATG-3’
79
Answer:
DNA 5’-CGTATG-3’
DNA 3’-GCATAC-5’
80
Review Proteins
!!!
Text pages 99-105
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82
Molecular Genetics
Reading and Questions
• Read through the article…
• Diagram in your notes the
role of m-rna and t-rna
• Answer questions 1-18 in
your notebooks
• Be prepared to share your
responses…
• Finished ? Work on Study
Guide
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