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Ch 12: DNA and RNA
12–1 DNA
A. Griffith and Transformation
1. In 1928, British scientist Fredrick Griffith was trying to
learn how certain types of bacteria caused pneumonia.
2. He isolated two different strains of pneumonia bacteria
from mice and grew them in his lab.
3. Griffith made two observations:
a. The disease-causing strain of bacteria grew into
smooth colonies on culture plates.
b. The harmless strain grew into colonies with rough
edges.
4. Griffith set up four individual experiments.
a. Experiment 1: Mice were injected with the diseasecausing strain of bacteria. The mice developed
_________________.
b. Experiment 2: Mice were injected with the harmless
strain of bacteria. These mice _______________.
c. Experiment 3: Griffith heated the disease-causing
bacteria. He then injected the heat-killed bacteria
into the mice. The mice ___________.
d. Experiment 4: Griffith mixed his heat-killed,
disease-causing bacteria with live, harmless bacteria
and injected the mixture into the mice. The mice
____________________________.
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5. Griffith concluded that the heat-killed bacteria passed
their disease-causing ability to the harmless strain.
6. Griffith called this process transformation because one
strain of bacteria (the harmless strain) had changed
permanently into another (the disease-causing strain).
7. Griffith hypothesized that a factor must contain
information that could change harmless bacteria into
disease-causing ones.
B. Avery and DNA
1. _______________ repeated Griffith’s work to determine
which molecule was most important for transformation.
2. Avery and his colleagues made an extract from the heatkilled bacteria that they treated with enzymes.
3. The enzymes destroyed proteins, lipids, carbohydrates,
and other molecules, including the nucleic acid RNA.
4. Transformation still occurred.
5. Avery and other scientists repeated the experiment using
enzymes that would break down DNA.
6. When ___________, transformation did not occur. They
concluded that DNA was the transforming factor.
7. Avery and other scientists discovered that the nucleic
acid DNA __________________________________
from one generation of an organism to the next.
C. The Hershey-Chase Experiment
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1. Alfred Hershey and Martha Chase studied ________—
_____________________ than a cell that can infect
living organisms.
2. ___________________- a virus that infects bacteria
3. Bacteriophages are composed of a DNA or RNA core
and a protein coat.
4. When a bacteriophage enters a bacterium, the virus
attaches to the surface of the cell and
___________________________ into it.
5. The viral genes produce many new bacteriophages,
which eventually destroy the bacterium.
6. When the cell splits open, hundreds of new viruses burst
out.
7. If Hershey and Chase could determine which part of the
virus entered an infected cell, they would learn whether
genes were made of protein or DNA.
8. They grew viruses in cultures containing radioactive
isotopes of phosphorus-32 (32P) and sulfur-35 (35S).
9. If 35S was found in the bacteria, it would mean that the
viruses’ protein had been injected into the bacteria.
10. If ______ was found in the bacteria, then it was
the DNA that had been injected.
11. Nearly all the radioactivity in the bacteria was from
phosphorus (32P).
12. Hershey and Chase concluded __________
_________________________________________.
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Activity: Genetic Material 
Label the DNA with radioactive label, and the DNA without
radioactive label
~ What did Hershey and Chase conclude was the genetic
material of the virus? DNA or protein
D. The Components and Structure of DNA
1. DNA is made up of _______________________.
2. _________________- a monomer of nucleic acids
3. DNA is composed of:
a. a five-carbon sugar called _______________
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b. a phosphate group
c. a nitrogenous base.
i. There are four kinds of bases in in DNA:
1. __________ (A)
2. __________ (G)
3. __________ (C)
4. __________ (T)
4. The backbone of a DNA chain is formed by sugar and
phosphate groups of each nucleotide.
5. The nucleotides can be joined together in any order
E. Chargaff’s Rules
1. Erwin Chargaff discovered that:
a. The percentages of guanine [G] and cytosine [C]
bases are ___________ in any sample of DNA.
b. The percentages of adenine [A] and thymine [T]
bases are __________ in any sample of DNA.
F. X-ray Evidence
1. _____________________ used X-ray diffraction to get
information about the structure of DNA.
2. She aimed an X-ray beam at concentrated DNA samples
and recorded the scattering pattern of the X-rays on film.
G. The Double Helix
1. Using clues from Franklin’s pattern, James Watson and
Francis Crick built a model that explained how DNA
carried information and could be copied.
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2. Watson and Crick's model of DNA was a double helix, in
which two strands were wound around each other.
3. Watson and Crick discovered that hydrogen bonds can
form only between certain base pairs—adenine and
thymine, and guanine and cytosine.
4. This principle is
called base
pairing
Activity: Base
Paring 
- write the missing
letter to complete
the base pair
~ What nucleotide is
always paired with
thymine?
~ What are the 3
parts of a DNA
nucleotide?
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12–2 Chromosomes and DNA Replication
A. DNA and Chromosomes
1. In prokaryotic cells, DNA is located in the cytoplasm.
2. Most prokaryotes have a single DNA molecule
containing nearly all of the cell’s genetic information.
3. Many eukaryotes have 1000 times the amount of DNA as
prokaryotes.
4. Eukaryotic DNA is located in the cell nucleus inside
chromosomes.
5. The number of chromosomes varies widely from one
species to the next.
B. Chromosome Structure
1. Eukaryotic chromosomes contain DNA and protein,
tightly packed together to form chromatin.
2. Chromatin consists of DNA tightly coiled around
proteins called histones.
3. DNA and histone molecules form nucleosomes.
4. Nucleosomes pack together, forming a thick fiber.
C. DNA Replication
1. Each strand of the DNA double helix has all the
information needed to reconstruct the other half by the
mechanism of base pairing.
2. In most prokaryotes, DNA replication begins at a single
point and continues in two directions.
3. In eukaryotic chromosomes, DNA replication occurs at
hundreds of places.
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4. Replication fork- the site where separation and
replication occur
D. Duplicating DNA
1. Before a cell divides, it duplicates its DNA in a process
called replication.
2. Replication ensures that each resulting cell will have a
complete set of DNA.
3. During DNA replication, the DNA molecule separates
into two strands, then produces two new complementary
strands following the rules of base pairing. Each strand
of the double helix of DNA serves as a template for the
new strand.
E. How Replication Occurs
1. DNA replication is carried out by enzymes that “unzip” a
molecule of DNA.
2. Hydrogen bonds between base pairs are broken and the
two strands of DNA unwind.
3. The principal enzyme involved in DNA replication is
DNA polymerase.
4. DNA polymerase joins individual nucleotides to produce
a DNA molecule and then “proofreads” each new DNA
strand.
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12–3 RNA and Protein Synthesis
A. Introduction
1. Genes are coded DNA instructions that control the
production of proteins.
2. Genetic messages can be decoded by copying part of the
nucleotide sequence from DNA into RNA.
3. RNA contains coded information for making proteins.
B. The Structure of RNA
6. RNA consists of a long chain of nucleotides.
7. Each nucleotide is made up of:
a. a 5-carbon sugar called ribose
b. a phosphate group
c. a nitrogenous base
8. There are three main differences between RNA and
DNA:
a. The sugar in RNA is ribose instead of deoxyribose.
b. RNA is generally single-stranded.
c. RNA contains uracil in place of thymine.
i. A bonds with U
ii. G bonds with C
9. There are three main types of RNA:
a. messenger RNA (mRNA) has the instructions for
joining amino acids to make protein
b. Proteins are assembled on ribosomes. Ribosomes
are made up of proteins and ribosomal RNA (rRNA)
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c. During protein construction transfer RNA (tRNA)
transfers each amino acid to the ribosome.
C. Transcription
1. Transcription- RNA molecules are produced by copying
part of a nucleotide sequence of DNA into a
complementary sequence in RNA.
a. Transcription requires the enzyme RNA polymerase.
2. During transcription, RNA polymerase binds to DNA
and separates the DNA strands.
3. RNA polymerase then uses one strand of DNA as a
template from which nucleotides are assembled into a
strand of RNA.
4. RNA polymerase binds only to regions of DNA known
as promoters.
5. Promoters are signals in DNA that indicate to the
enzyme where to bind to make RNA.
6. RNA Editing
a. The DNA of eukaryotic genes contains sequences of
nucleotides, called introns, that are not involved in
coding for proteins.
b. The DNA sequences that code for proteins are called
exons
c. When RNA molecules are formed, introns and exons
are copied from DNA.
d. The introns are cut out of RNA molecules.
e. The exons are the spliced together to form mRNA
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Activity: Transcription 
- label the DNA and RNA
- label the missing nucleotides marked on the diagram
~ In RNA what nucleotide is always paired with uracil?
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Activity: Decoding mRNA 
- write the amino acid that corresponds to each mRNA code.
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D. The Genetic Code
1. The genetic code is the “language” of mRNA
instructions.
2. The code is written using four “letters” (the bases: A, U,
C, and G).
3. Codon- consists of three consecutive nucleotides on
mRNA that specify a particular amino acid.
4. Each codon specifies a particular amino acid that is to be
placed on the polypeptide chain.
5. Some amino acids can be specified by more than one
codon.
6. There is one codon AUG that can either specify the
amino acid methionine or serve as a “start” codon for
protein synthesis.
7. There are three “stop” codons that do not code for any
amino acid. These “stop” codons signify the end of a
polypeptide.
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Activity: Comparing DNA Replication and Transcription -
fill in the missing information. One row has been completed
for you
E. Translation
1. Translation is the decoding of an mRNA message into a
polypeptide chain (protein).
2. Translation takes place on ribosomes.
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3. During translation, the cell uses information from
messenger RNA to produce proteins.
4. Translation is the decoding of an mRNA message into a
polypeptide chain (protein).
5. Translation begins when an mRNA molecule attaches to
a ribosome.
6. As each codon of the mRNA molecule moves through
the ribosome, the proper amino acid is brought into the
ribosome by tRNA.
7. In the ribosome, the amino acid is transferred to the
growing polypeptide chain.
8. Each tRNA molecule carries only one kind of amino
acid.
9. In addition to an amino acid, each tRNA molecule has
three unpaired bases.
10. These bases, called the anticodon, are
complementary to one mRNA codon.
11. The ribosome binds new tRNA molecules and
amino acids as it moves along the mRNA.
12. The process continues until the ribosome reaches a
stop codon.
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Activity: Translation 
- Number the four tRNA anticodons in the order in which they
should appear to match the codons in the mRNA strand
F. The Roles of RNA and DNA
1. The cell uses the DNA “master plan” to prepare RNA
“blueprints.” The DNA stays in the nucleus.
2. The RNA molecules go to the protein building sites in
the cytoplasm—the ribosomes.
3. Genes contain instructions for assembling proteins.
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4. Many proteins are enzymes, which catalyze and regulate
chemical reactions.
5. Proteins are each specifically designed to build or
operate a component of a living cell.
6. The sequence of bases in DNA is used as a template for
mRNA.
7. The codons of mRNA specify the sequence of amino
acids in a protein.
12–4 Mutations
A. Kinds of Mutations
1. Mutations are changes in the genetic material.
2. Gene mutations- mutations that produce changes in a
single gene
3. Chromosomal mutations- mutations that produce
changes in whole chromosomes
B. Gene mutations
1. Gene mutations involving a change in one or a few
nucleotides are known as point mutations because they
occur at a single point in the DNA sequence.
2. Point mutations include substitutions, insertions, and
deletions.
a. Substitutions- usually affect no more than a single
amino acid.
b. Frameshift mutation- an insertion or deletion of a
nucleotide
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i. Are usually more dramatic because it causes a
shift in the grouping of codons.
ii. Frameshift mutations may change every amino
acid that follows the point of the mutation.
iii. Frameshift mutations can alter a protein so
much that it is unable to perform its normal
functions.
c. Insertion- an extra base is inserted into a base
sequence
d. Deletion- the loss of a single base is deleted and the
reading frame is shifted.
C. Chromosomal Mutations
1. Chromosomal mutations
involve changes in the
number or structure of
chromosomes.
2. Chromosomal mutations
include deletions,
duplications, inversions,
and translocations.
a. Deletions- involve
the loss of all or
part of a chromosome.
b. Duplications- produce extra copies of parts of a
chromosome.
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c. Inversions- reverse the direction of parts of
chromosomes.
d. Translocations- occurs when part of one
chromosome breaks off and attaches to another.
D. Significance of Mutations
1. Many mutations have little or no effect on gene
expression.
2. Some mutations are the cause of genetic disorders.
3. Beneficial mutations may produce proteins with new or
altered activities that can be useful.
4. Polyploidy is the condition in which an organism has
extra sets of chromosomes.
12-5 Gene Regulation
A. Gene Regulation: An Example
1. E. coli provides an example of how gene expression can
be regulated.
2. Operon- a group of genes that operate together.
3. In E. coli, these genes must be turned on so the
bacterium can use lactose as food.
a. Therefore, they are called the lac operon.
4. The lac genes are turned off by repressors and turned on
by the presence of lactose.
5. On one side of the operon's three genes are two
regulatory regions.
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a. In the promoter (P) region, RNA polymerase binds
and then begins transcription.
b. The other region is the operator (O).
6. When the lac repressor binds to the O region,
transcription is not possible.
7. When lactose is added, sugar binds to the repressor
proteins.
8. The repressor protein changes shape and falls off the
operator and transcription is made possible.
9. Many genes are regulated by repressor proteins.
10. Some genes use proteins that speed transcription.
11. Sometimes regulation occurs at the level of protein
synthesis
B. Eukaryotic Gene Regulation
1. Operons are generally not found in eukaryotes.
2. Most eukaryotic genes are controlled individually and
have regulatory sequences that are much more complex
than those of the lac operon.
3. Many eukaryotic genes have a sequence called the
TATA box.
4. The TATA box seems to help position RNA polymerase.
5. Eukaryotic promoters are usually found just before the
TATA box, and consist of short DNA sequences.
6. Genes are regulated in a variety of ways by enhancer
sequences.
7. Many proteins can bind to different enhancer sequences.
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8. Some DNA-binding proteins enhance transcription by:
a. opening up tightly packed chromatin
b. helping to attract RNA polymerase
c. blocking access to genes.
Activity: Gene Regulation 
- Label the repressor, operators and genes in each diagram
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C. Development and Differentiation
1. As cells grow and divide, they undergo differentiation,
meaning they become specialized in structure and
function.
2. Hox genes control the differentiation of cells and tissues
in the embryo.
3. Careful control of expression in hox genes is essential for
normal development.
4. All hox genes are descended from the genes of common
ancestors.
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