Chapter 12 Molecular Genetics
Section 1: DNA: The Genetic Material
Section 2: Replication of DNA
Section 3: DNA, RNA, and Protein
Section 4: Gene Regulation and Mutation
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Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Griffith
 Performed the first major experiment that led to
the discovery of DNA as the genetic material
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Avery
 Identified the molecule that transformed the
R strain of bacteria into the S strain
 Concluded that when the S cells were killed,
DNA was released
 R bacteria incorporated this DNA into their
cells and changed into S cells.
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Hershey and Chase
 Used radioactive labeling to
trace the DNA and protein
 Concluded that the viral
DNA was injected into the
cell and provided the
genetic information needed
to produce new viruses
Chapter 12 Molecular Genetics
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
DNA Structure
 Nucleotides
 Consist of a five-carbon sugar, a phosphate
group, and a nitrogenous base
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Chargaff
 Chargaff’s rule:
C = G and T = A
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
X-ray Diffraction
 X-ray diffraction data helped solve the
structure of DNA
 Indicated that DNA was a double helix
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Watson and Crick
 Built a model of the double helix that
conformed to the others’ research
1. two outside strands consist of alternating
deoxyribose and phosphate
2. cytosine and guanine bases pair to each
other by three hydrogen bonds
3. thymine and adenine bases pair to each
other by two hydrogen bonds
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
DNA Structure
 DNA often is compared to a twisted ladder.
 Rails of the ladder are represented by the
alternating deoxyribose and phosphate.
 The pairs of bases (cytosine–guanine or
thymine–adenine) form the steps.
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Orientation
 On the top rail, the strand is said to be oriented 5′ to 3′.
 The strand on the bottom runs in the opposite
direction and is oriented 3′ to 5′.
Chapter 12 Molecular Genetics
12.1 DNA: The Genetic Material
Chromosome Structure
 DNA coils around histones to form nucleosomes,
which coil to form chromatin fibers.
 The chromatin fibers supercoil to form chromosomes
that are visible in the metaphase stage of mitosis.
Chapter 12 Molecular Genetics
12.2 Replication of DNA
Semiconservative Replication
 Parental strands of
DNA separate, serve
as templates, and
produce DNA
molecules that have
one strand of
parental DNA and
one strand of new DNA.
Chapter 12 Molecular Genetics
12.2 Replication of DNA
Unwinding
 DNA helicase, an enzyme, is responsible for
unwinding and unzipping the double helix.
 RNA primase adds a short segment of RNA,
called an RNA primer, on each DNA strand.
Chapter 12 Molecular Genetics
12.2 Replication of DNA
Base pairing
 DNA polymerase continues adding appropriate
nucleotides to the chain by adding to the 3′ end
of the new DNA strand.
Chapter 12 Molecular Genetics
Chapter 12 Molecular Genetics
12.2 Replication of DNA
 One strand is called the leading strand
and is elongated as the DNA unwinds.
 The other strand of DNA, called the
lagging strand, elongates away from
the replication fork.
 The lagging strand is synthesized
discontinuously into small segments,
called Okazaki fragments.
Chapter 12 Molecular Genetics
12.2 Replication of DNA
Joining
 DNA polymerase removes the RNA primer
and fills in the place with DNA nucleotides.
 DNA ligase links the two sections.
Chapter 12 Molecular Genetics
12.2 Replication of DNA
Comparing DNA Replication in Eukaryotes
and Prokaryotes
 Eukaryotic DNA unwinds in multiple areas
as DNA is replicated.
 In prokaryotes, the circular DNA strand is
opened at one origin of replication.
Chapter 12 Molecular Genetics
12.3 DNA, RNA, and Protein
Central Dogma
 RNA
 Contains the sugar ribose and the
base uracil
 Usually is single stranded
Chapter 12 Molecular Genetics
12.3 DNA, RNA, and Protein
Messenger RNA (mRNA)
 Long strands of RNA nucleotides that are
formed complementary to one strand of DNA
Ribosomal RNA (rRNA)
 Associates with proteins to form ribosomes
in the cytoplasm
Transfer RNA (tRNA)
 Smaller segments of RNA nucleotides that
transport amino acids to the ribosome
Chapter 12 Molecular Genetics
12.3 DNA, RNA, and Protein
Chapter 12 Molecular Genetics
Chapter 12 Molecular Genetics
12.3 DNA, RNA, and Protein
Transcription
 Through transcription,
the DNA code is
transferred to mRNA
in the nucleus.
 DNA is unzipped in
the nucleus and RNA
polymerase binds to a specific section where an
mRNA will be synthesized.
Chapter 12 Molecular Genetics
Chapter 12 Molecular Genetics
12.3 DNA, RNA, and Protein
RNA Processing
 The code on the DNA is interrupted
periodically by sequences that are not in the
final mRNA.
 Intervening sequences are called introns.
 Remaining pieces of DNA that serve as the
coding sequences are called exons.
DNA and
Genes
Chapter 12 Molecular Genetics
12.3 DNA, RNA, and Protein
The Code
 Experiments during the 1960s demonstrated
that the DNA code was a three-base code.
 The three-base code in DNA or mRNA is
called a codon.
Chapter 12 Molecular Genetics
12.3 DNA, RNA, and Protein
Translation
 In translation, tRNA
molecules act as the
interpreters of the mRNA
codon sequence.
 At the middle of the folded
strand, there is a three-base
coding sequence called the
anticodon.
 Each anticodon is
complementary to a codon
on the mRNA.
Chapter 12 Molecular Genetics
12.3 DNA, RNA, and Protein
Visualizing
Transcription
and Translation
Chapter 12 Molecular Genetics
12.3 DNA, RNA, and Protein
One Gene—
One Enzyme
 The Beadle and Tatum
experiment showed
that one gene codes
for one enzyme. We
now know that one
gene codes for one
polypeptide.
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
Prokaryote Gene Regulation
 Ability of an organism to control which genes
are transcribed in response to the environment
 An operon is a section of DNA that contains the
genes for the proteins needed for a specific
metabolic pathway.
 Operator
 Promoter
 Regulatory gene
 Genes coding for proteins
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
The Trp Operon
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
The Lac Operon
Lac-Trp Operon
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
Eukaryote Gene Regulation
 Controlling transcription
 Transcription factors ensure that a gene
is used at the right time and that proteins
are made in the right amounts
 The complex structure of eukaryotic DNA
also regulates transcription.
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
Hox Genes
 Hox genes are
responsible for
the general body
pattern of most
animals.
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
RNA Interference
 RNA interference can stop the mRNA from
translating its message.
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
Mutations
 A permanent change that occurs in a cell’s
DNA is called a mutation.
 Types of mutations
 Point mutation
 Insertion
 Deletion
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
Protein Folding and Stability
 Substitutions also can lead to genetic
disorders.
 Can change both the folding and stability
of the protein
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
Causes of Mutation
 Can occur spontaneously
 Chemicals and radiation also can
damage DNA.
 High-energy forms of radiation, such as X rays
and gamma rays, are highly mutagenic.
Chapter 12 Molecular Genetics
12.4 Gene Regulation and Mutation
Body-cell v. Sex-cell Mutation
 Somatic cell mutations are not passed on
to the next generation.
 Mutations that occur in sex cells are passed
on to the organism’s offspring and will be
present in every cell of the offspring.
Chapter 12 Molecular Genetics
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Formative Test Questions
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Standardized Test Practice
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Chapter 12 Molecular Genetics
Chapter Diagnostic
Questions
Which scientist(s) definitively proved
that DNA transfers genetic material?
A. Watson and Crick
B. Mendel
C. Hershey and Chase
D. Avery
Chapter 12 Molecular Genetics
Chapter Diagnostic
Questions
Name the small segments of the lagging
DNA strand.
A. ligase
B. Okazaki fragments
C. polymerase
D. helicase
Chapter 12 Molecular Genetics
Chapter Diagnostic
Questions
Which is not true of RNA?
A. It contains the sugar ribose.
B. It contains the base uracil.
C. It is single-stranded.
D. It contains a phosphate.
Chapter 12 Molecular Genetics
12.1 Formative
Questions
The experiments of Avery, Hershey and
Chase provided evidence that the carrier
of genetic information is _______.
A. carbohydrate
B. DNA
C. lipid
D. protein
Chapter 12 Molecular Genetics
12.1 Formative
Questions
What is the base-pairing rule for purines
and pyrimidines in the DNA molecule?
A. A—G and C—T
B. A—T and C—G
C. C—A and G—T
D. C—U and A—G
Chapter 12 Molecular Genetics
12.1 Formative
Questions
What are chromosomes composed of?
A.chromatin and histones
B. DNA and protein
C. DNA and lipids
D. protein and centromeres
Chapter 12 Molecular Genetics
12.2 Formative
Questions
True or False
The work of Watson and Crick solved
the mystery of how DNA works as a
genetic code.
Chapter 12 Molecular Genetics
12.2 Formative
Questions
Which is not an enzyme involved in DNA
replication?
A. DNA ligase
B. DNA polymerase
C. hilicase
D. RNA primer
Chapter 12 Molecular Genetics
12.2 Formative
Questions
During DNA replication, what nucleotide
base sequence is synthesized along an
original strand that has the sequence
TCAAGC?
A. AGTTCG
B. ATGGCG
C. CTGGAT
D. GACCTA
Chapter 12 Molecular Genetics
12.3 Formative
Questions
Which shows the basic chain of events
in all organisms for reading and expressing
genes?
A. DNA RNA protein
B. RNA DNA protein
C. mRNA rRNA
tRNA
D. RNA processing transcription
translation
Chapter 12 Molecular Genetics
12.3 Formative
Questions
In the RNA molecule, uracil replaces
_______.
A. adenine
B. cytosine
C. purine
D. thymine
Chapter 12 Molecular Genetics
12.3 Formative
Questions
Which diagram shows messenger
RNA (mRNA)?
A.
C.
B.
D.
Chapter 12 Molecular Genetics
12.3 Formative
Questions
What characteristic of the mRNA molecule
do scientists not yet understand?
Chapter 12 Molecular Genetics
12.3 Formative
Questions
A. intervening sequences in the mRNA molecule
called introns
B. the original mRNA made in the nucleus called
the pre-mRNA
C. how the sequence of bases in the mRNA
molecule codes for amino acids
D. the function of many adenine nucleotides
at the 5′ end called the poly-A tail
Chapter 12 Molecular Genetics
12.4 Formative
Questions
Why do eukaryotic cells need a complex
control system to regulate the expression
of genes?
Chapter 12 Molecular Genetics
12.4 Formative
Questions
A. All of an organism’s cells transcribe the same
genes.
B. Expression of incorrect genes can lead to
mutations.
C. Certain genes are expressed more frequently
than others are.
D. Different genes are expressed at different
times in an organism’s lifetime.
Chapter 12 Molecular Genetics
12.4 Formative
Questions
Which type of gene causes cells to
become specialized in structure in
function?
A. exon
B. Hox gene
C. intron
D. operon
Chapter 12 Molecular Genetics
12.4 Formative
Questions
What is an immediate result of a mutation
in a gene?
A. cancer
B. genetic disorder
C. nonfunctional enzyme
D. amino acid deficiency
Chapter 12 Molecular Genetics
12.4 Formative
Questions
Which is the most highly mutagenic?
A. chemicals in food
B. cigarette smoke
C. ultraviolet radiation
D. X rays
Chapter 12 Molecular Genetics
Chapter Assessment
Questions
Look at the following figure. Identify the
proteins that DNA first coils around.
Chapter 12 Molecular Genetics
Chapter Assessment
Questions
A. chromatin fibers
B. chromosomes
C. histones
D. nucleosome
Chapter 12 Molecular Genetics
Chapter Assessment
Questions
Explain how Hox genes affect an organism.
A. They determine size.
B. They determine body plan.
C. They determine sex.
D. They determine number
of body segments.
Chapter 12 Molecular Genetics
Chapter Assessment
Questions
Explain the difference between body-cell
and sex-cell mutation.
Chapter 12 Molecular Genetics
Chapter Assessment
Questions
Answer: A mutagen in a body cell becomes
part of the of the genetic sequence
in that cell and in future daughter
cells. The cell may die or simply not
perform its normal function. These
mutations are not passed on to the
next generation. When mutations
occur in sex cells, they will be
present in every cell of the offspring.
Chapter 12 Molecular Genetics
Standardized Test
Practice
What does this
diagram show about
the replication of DNA
in eukaryotic cells?
Chapter 12 Molecular Genetics
Standardized Test
Practice
A. DNA is replicated only at certain places along
the chromosome.
B. DNA replication is both semicontinuous and
conservative.
C. Multiple areas of replication occur along the
chromosome at the same time.
D. The leading DNA strand is synthesized
discontinuously.
Chapter 12 Molecular Genetics
Standardized Test
Practice
What is this process called?
Chapter 12 Molecular Genetics
Standardized Test
Practice
A. mRNA processing
B. protein synthesis
C. transcription
D. translation
Chapter 12 Molecular Genetics
Standardized Test
Practice
What type of mutation results in this change
in the DNA sequence?
TTCAGG
A. deletion
B. frameshift
C. insertion
D. substitution
TTCTGG
Chapter 12 Molecular Genetics
Standardized Test
Practice
How could RNA interference be used
to treat diseases such as cancer and
diabetes?
Chapter 12 Molecular Genetics
Standardized Test
Practice
A. by activating genes to produce proteins that
can overcome the disease
B. by interfering with DNA replication in cells
affected by the disease
C. by preventing the translation of mRNA into
the genes associated with the disease
D. by shutting down protein synthesis in the
cells of diseased tissues
Chapter 12 Molecular Genetics
Standardized Test
Practice
True or False
The structure of a protein can be altered
dramatically by the exchange of a single
amino acid for another.
Chapter 12 Molecular Genetics
Glencoe Biology Transparencies
Chapter 12 Molecular Genetics
Image Bank
Chapter 12 Molecular Genetics
Image Bank
Chapter 12 Molecular Genetics
Vocabulary
Section 1
double helix
nucleosome
Chapter 12 Molecular Genetics
Vocabulary
Section 2
semiconservative replication
DNA polymerase
Okazaki fragment
Chapter 12 Molecular Genetics
Vocabulary
Section 3
RNA
intron
messenger RNA
exon
ribosomal RNA
translation
transfer RNA
transcription
RNA polymerase
codon
Chapter 12 Molecular Genetics
Vocabulary
Section 4
gene regulation
operon
mutation
mutagen
Chapter 12 Molecular Genetics
Animation
 DNA Polymerase
 Transcription
 Visualizing Transcription and
Translation
 Lac-Trp Operon