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Interest Grabber
Section 12-1
Order! Order!
Genes are made of DNA, a large, complex molecule. DNA is composed of
individual units called nucleotides. Three of these units form a code. The
order, or sequence, of a code and the type of code determine the meaning
of the message.
1. On a sheet of paper, write the word cats. List the letters or units that
make up the word cats.
2. Try rearranging the units to form other words. Remember that each
new word can have only three units. Write each word on your paper,
and then add a definition for each word.
3. Did any of the codes you formed have the same meaning?
4. How do you think changing the order of the nucleotides in the
DNA codon changes the codon’s message?
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Section:
Section Outline
Section 12-1
12–1
DNA
A. Griffith and Transformation
1. Griffith’s Experiments
2. Transformation
B. Avery and DNA
C. The Hershey-Chase Experiment
1. Bacteriophages
2. Radioactive Markers
D. The Components and Structure of DNA
1. Chargaff’s Rules
2. X-Ray Evidence
3. The Double Helix
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Section:
Fred Griffith’s
Transformation
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Section:
Avery’s Experiment
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Frederick Griffith’s Experiment
Mice infected with live coated bacteria (S strain) died of pneumonia
Mice infected with live uncoated bacteria (R strain) survived
Mice infected with heat killed coated bacteria (S strain) survived
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Frederick Griffith’s Experiment
Mice infected with both live uncoated bacteria and heat killed coated
bacteria died
 30156-9
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Figure 12–4 Hershey-Chase Experiment
Section 12-1
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Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Figure 12–4 Hershey-Chase Experiment
Section 12-1
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Section:
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Figure 12–4 Hershey-Chase Experiment
Section 12-1
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Section:
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Structure of DNA
DNA is made of
chains of nucleotides
a Nucleotide is made
of three subunits
– phosphorus group
– 5 carbon sugar
group
– nitrogenous base
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Section:
Structure of DNA
DNA has four types of
nucleotides, each with a
different nitrogenous
base:
–
–
–
–
A=Adenine
G=Guanine
C=Cytosine
T=Thymine
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Section:
Figure 12–5 DNA Nucleotides
Section 12-1
Purines
Adenine
Guanine
Phosphate
group
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Section:
Pyrimidines
Cytosine
Thymine
Deoxyribose
Percentage of Bases in Four Organisms
Section 12-1
Source of DNA
A
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8
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Section:
Chargaff’s Rule
Chargaff found that the amount of adenine in an organism is always equal
to the amount of thymine (A=T)
Also, he found that the amount of cytosine always equals the amount of
guanine (C=G).
This suggested that DNA had some sort of regular structure where the
pairing of these bases are involved
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Section:
Cytosine makes up 38% of the nucleotides in a
sample of DNA from an organism. What
percent of the nucleotides in this sample will
be thymine?
A.
B.
C.
D.
E.
12
24
31
38
It cannot be determined from the
information provided.
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Section:
In an analysis of the nucleotide composition of DNA, which of the following is true?
A. A = C
B. A = G and C = T
C. A + C = G + T
D. A + T = G + C
E. Both B and C are true
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Section:
In analyzing the number of different bases
in a DNA sample, which result would be consistent with the base-pairing
rules?
– A=G
– A+G=C+T
– A+T=G+T
– A=C
– G=T
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Section:
Franklin
Franklin did X-ray diffraction studies on DNA
Photographs suggested that the DNA molecule resembled a tightly coiled
spring - a helix
 30167
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Section:
Figure 16.6 Rosalind Franklin and her X-ray diffraction
photo of DNA
(a) Rosalind Franklin
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Section:
(b) Franklin’s X-ray diffraction
Photograph of DNA
X-Ray diffraction of DNA
indicated that DNA was
2nm thick and has a
helical structure, one full
turn every 3.4nm, 10
bases per turn
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WATSON AND CRICK
Using Chargaff’s rule and the information from Franklin about the shape of
DNA
Watson & Crick determined the structure of the DNA molecule and how it
makes a copy of itself.
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Section:
WATSON AND CRICK
DNA is made of two strands of nucleotides chains that wind around each
other
This DNA structure is called a:
– double helix
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Section:
Figure 12–7 Structure of DNA
Section 12-1
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
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Section:
Interest Grabber
Section 12-2
A Perfect Copy
When a cell divides, each daughter cell receives a complete set of
chromosomes. This means that each new cell has a complete set of the
DNA code. Before a cell can divide, the DNA must be copied so that there
are two sets ready to be distributed to the new cells.
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Section:
Interest Grabber continued
Section 12-2
1. On a sheet of paper, draw a curving or zig-zagging line that divides the
paper into two halves. Vary the bends in the line as you draw it. Without
tracing, copy the line on a second sheet of paper.
2. Hold the papers side by side, and compare the lines. Do they look the
same?
3. Now, stack the papers, one on top of the other, and hold the papers up
to the light. Are the lines the same?
4. How could you use the original paper to draw exact copies of the line
without tracing it?
5. Why is it important that the copies of DNA that are given to new
daughter cells be exact copies of the original?
Go to
Section:
Section Outline
Section 12-2
12–2
Chromosomes and DNA Replication
A. DNA and Chromosomes
1. DNA Length
2. Chromosome Structure
B. DNA Replication
1. Duplicating DNA
2. How Replication Occurs
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Section:
Prokaryotic Chromosome Structure
Section 12-2
Chromosome
E. coli bacterium
Bases on the chromosome
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Section:
Figure 12-10 Chromosome Structure
of Eukaryotes
Section 12-2
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
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Section:
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WATSON AND CRICK
The double helix looks like a twisted ladder
The sides of the ladder are made of alternating sugar and phosphate
groups
– the sugar and phosphate groups form the backbone of the DNA
molecule
The steps or rungs of the ladder are made of nitrogenous base pairs
 30168-70
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Section:
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WATSON AND CRICK
Adenine and Guanine are double ring structures called purines
Cytosine and Thymine are single ring structures called pyrimidines
In DNA, A always pairs with T and
G always pairs with C
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Section:
A Purine always
pairs with a
Pyrimidine
A with T
G with C.
X-Ray diffraction
of DNA indicated
that DNA was 2nm
thick
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Antiparallel
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DNA REPLICATION
DNA must make a copy of itself during Interphase
Watson and Crick postulated that the DNA molecule unzipped itself
between the bases (because of the weak bonds)
– Once opened, the exposed bases could serve as a template,
allowing floating nucleotides to bond with them and follow their
pattern in forming new DNA strands
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Section:
Link to DNA Replication
DEMO
Old DNA
strands act as
a template for
the new DNA
strands
New DNA is
half old and
half new
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Section:
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1. What do the yellow
strands of DNA
represent?
new DNA
strands
Semi-conservative replication
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Section:
Figure 12–11 DNA Replication
occurs at replication bubbles
Section 12-2
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
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Section:
Original
strand
Nitrogenous
bases
Telomeres include incomplete ends to the
DNA
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Section:
telomere
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Telomeres protect the ends of the DNA, but
become shorter during each replication
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Interest Grabber Answers
1. On a sheet of paper, write the word cats. List the letters or units that make
up the word cats.
The units that make up cats are c, a, t, and s.
2. Try rearranging the units to form other words. Remember that each
new word can have only three units. Write each word on your paper, and
then add a definition for each word.
Student codes may include: Act; Sat; Cat
3. Did any of the codes you formed have the same meaning?
No
4. How do you think changing the order of the nucleotides in the DNA codon
changes the codon’s message?
Changing the order of the nucleotides changes the meaning of the codon.
Interest Grabber Answers
1. On a sheet of paper, draw a curving or zig-zagging line that divides the paper
into two halves. Vary the bends in the line as you draw it. Without tracing,
copy the line on a second sheet of paper.
2. Hold the papers side by side, and compare the lines. Do they look the same?
Lines will likely look similar.
3. Now, stack the papers, one on top of the other, and hold the papers up to the
light. Are the lines the same?
Overlaying the papers will show variations in the lines.
4. How could you use the original paper to draw exact copies of the line without
tracing it?
Possible answer: Cut along the line and use it as a template to draw the line
on another sheet of paper.
5. Why is it important that the copies of DNA that are given to new daughter
cells be exact copies of the original?
Each cell must have the correct DNA, or the cell will not
have the correct characteristics.
Interest Grabber Answers
1. Why do you think the library holds some books for reference only?
Possible answers: The books are too valuable to risk loss or damage to
them. The library wants to make sure the information is always available
and not tied up by one person.
2. If you can’t borrow a book, how can you take home the information in it?
Students may suggest making a photocopy or taking notes.
3. All of the parts of a cell are controlled by the information in DNA, yet DNA
does not leave the nucleus. How do you think the information in DNA might
get from the nucleus to the rest of the cell?
Students will likely say that the cell has some way to copy the information
without damaging the DNA.
Interest Grabber Answers
1. Copy the following information about Protein X: Methionine—Phenylalanine—
Tryptophan—Asparagine—Isoleucine—STOP.
2. Use Figure 12–17 on page 303 in your textbook to determine one possible sequence of
RNA to code for this information. Write this code below the description of Protein X.
Below this, write the DNA code that would produce this RNA sequence.
Sequences may vary. One example follows: Protein X: mRNA: AUG-UUU-UGG-AAUAUU-UGA; DNA: TAC-AAA-ACC-TTA-TAA-ACT
3. Now, cause a mutation in the gene sequence that you just determined by deleting the
fourth base in the DNA sequence. Write this new sequence.
(with deletion of 4th base U) DNA: TAC-AAA-CCT-TAT-AAA-CT
4. Write the new RNA sequence that would be produced. Below that, write the amino acid
sequence that would result from this mutation in your gene. Call this Protein Y.
mRNA: AUG-UUU-GGA-AUA-UUU-GA Codes for amino acid sequence: Methionine—
Phenylalaine—Glycine—Isoleucine—Phenylalanine—?
5. Did this single deletion cause much change in your protein? Explain your answer.
Yes, Protein Y was entirely different from Protein X.
Interest Grabber Answers
1. Do you think that cells produce all the proteins for which the DNA (genes)
code? Why or why not? How do the proteins made affect the type and
function of cells?
Cells do not make all of the proteins for which they have genes (DNA).
The structure and function of each cell are determined by the types of
proteins present.
2. Consider what you now know about genes and protein synthesis. What
might be some ways that a cell has control over the proteins it produces?
There must be certain types of compounds that are involved in determining
what types of mRNA transcripts are made and when this mRNA translates
at the ribosome.
3. What type(s) of organic compounds are most likely the ones that help to
regulate protein synthesis? Justify your answer.
The type of compound responsible is probably a protein, specifically
enzymes, because these catalyze the chemical reactions
that take place.