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Chapter 10
Introduction
Molecular Biology of the Gene
 Viruses infect organisms by
– binding to receptors on a host’s target cell,
– injecting viral genetic material into the cell, and
– hijacking the cell’s own molecules and organelles to
produce new copies of the virus.
 The host cell is destroyed, and newly replicated
viruses are released to continue the infection.
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
© 2012 Pearson Education, Inc.
Introduction
Figure 10.0_1
Chapter 10: Big Ideas
 Viruses are not generally considered alive
because they
– are not cellular and
The Structure of the
Genetic Material
DNA Replication
The Flow of Genetic
Information from DNA to
RNA to Protein
The Genetics of Viruses
and Bacteria
– cannot reproduce on their own.
 Because viruses have much less complex
structures than cells, they are relatively easy to
study at the molecular level.
 For this reason, viruses are used to study the
functions of DNA.
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Figure 10.0_2
THE STRUCTURE OF THE
GENETIC MATERIAL
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1
10.1 SCIENTIFIC DISCOVERY: Experiments
showed that DNA is the genetic material
10.1 SCIENTIFIC DISCOVERY: Experiments
showed that DNA is the genetic material
 Until the 1940s, the case for proteins serving as
the genetic material was stronger than the case
for DNA.
 In 1928, Frederick Griffith discovered that a
“transforming factor” could be transferred into a
bacterial cell. He found that
– Proteins are made from 20 different amino acids.
– DNA was known to be made from just four kinds of
nucleotides.
– when he exposed heat-killed pathogenic bacteria to
harmless bacteria, some harmless bacteria were
converted to disease-causing bacteria and
– the disease-causing characteristic was inherited by
descendants of the transformed cells.
 Studies of bacteria and viruses
– ushered in the field of molecular biology, the study of
heredity at the molecular level, and
– revealed the role of DNA in heredity.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
10.1 SCIENTIFIC DISCOVERY: Experiments
showed that DNA is the genetic material
10.1 SCIENTIFIC DISCOVERY: Experiments
showed that DNA is the genetic material
 In 1952, Alfred Hershey and Martha Chase used
bacteriophages to show that DNA is the genetic
material of T2, a virus that infects the bacterium
Escherichia coli (E. coli).
– Bacteriophages (or phages for short) are viruses that
infect bacterial cells.
– The sulfur-labeled protein stayed with the phages outside
the bacterial cell, while the phosphorus-labeled DNA was
detected inside cells.
– Cells with phosphorus-labeled DNA produced new
bacteriophages with radioactivity in DNA but not in protein.
– Phages were labeled with radioactive sulfur to detect
proteins or radioactive phosphorus to detect DNA.
– Bacteria were infected with either type of labeled phage to
determine which substance was injected into cells and
which remained outside the infected cell.
Animation: Hershey-Chase Experiment
Animation: Phage T2 Reproductive Cycle
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© 2012 Pearson Education, Inc.
Figure 10.1A
Figure 10.1A_1
Head
DNA
Head
Tail
Tail fiber
Tail
Tail fiber
2
Figure 10.1B
Figure 10.1B_1
Phage
Bacterium
The radioactivity
is in the liquid.
Phage
DNA
DNA
Batch 1:
Radioactive
protein
labeled in
yellow
Bacterium
Empty
protein shell
Radioactive
protein
Phage
Empty
protein shell
Radioactive
protein
Centrifuge
Phage
DNA
DNA
Batch 1:
Radioactive
protein
labeled in
yellow
Pellet
1
3
2
2
1
4
Radioactive
DNA
Batch 2:
Radioactive
DNA labeled
in green
Centrifuge
Pellet
The radioactivity
is in the pellet.
Figure 10.1B_2
Radioactive
DNA
Batch 2:
Radioactive
DNA labeled
in green
Figure 10.1C
Empty
protein shell
The radioactivity
is in the liquid.
Phage
DNA
Centrifuge
Pellet
3
1 A phage attaches
4
itself to a bacterial
cell.
2 The phage injects
3 The phage DNA directs
its DNA into the
bacterium.
the host cell to make
more phage DNA and
proteins; new phages
assemble.
4 The cell lyses
and releases
the new phages.
Centrifuge
Pellet
The radioactivity
is in the pellet.
Figure 10.1C_1
Figure 10.1C_2
3
1
A phage attaches
itself to a bacterial
cell.
2
The phage injects
its DNA into the
bacterium.
The phage DNA directs
the host cell to make
more phage DNA and
proteins; new phages
assemble.
3
4
The cell lyses
and releases
the new phages.
3
10.2 DNA and RNA are polymers of nucleotides
10.2 DNA and RNA are polymers of nucleotides
 DNA and RNA are nucleic acids.
 Each type of DNA nucleotide has a different
nitrogen-containing base:
 One of the two strands of DNA is a DNA
polynucleotide, a nucleotide polymer (chain).
 A nucleotide is composed of a
– adenine (A),
– cytosine (C),
– nitrogenous base,
– thymine (T), and
– five-carbon sugar, and
– guanine (G).
– phosphate group.
 The nucleotides are joined to one another by a
sugar-phosphate backbone.
Animation: DNA and RNA Structure
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© 2012 Pearson Education, Inc.
Figure 10.2A
Figure 10.2A_1
T
A
C
T
A
C
Sugar-phosphate
backbone
G
T
A
C
A
C
A
C
Covalent
bond
joining
nucleotides
T
A
G
A
A
G
T
G
C
T
Phosphate
group
A
C
G
T
T
G
A
Nitrogenous
base
C
Nitrogenous base
(can be A, G, C, or T)
G
T
A
Sugar
C
G
C
G
G
T
A
A DNA
double helix
DNA
nucleotide
T
Thymine (T)
T
A
Phosphate
group
G
G
G
G
T
T
T
C
G
A
A
Sugar
(deoxyribose)
C
DNA nucleotide
G
T
A
A DNA
double helix
Two representations
of a DNA polynucleotide
Figure 10.2A_2
Figure 10.2A_3
Sugar-phosphate
backbone
A
A
Covalent
bond
joining
nucleotides
C
DNA
nucleotide
T
Phosphate
group
Nitrogenous base
(can be A, G, C, or T)
Nitrogenous
base
Sugar
C
Thymine (T)
T
Phosphate
group
G
G
G
G
Sugar
(deoxyribose)
DNA nucleotide
Two representations
of a DNA polynucleotide
4
Figure 10.2B
Figure 10.2B_1
Thymine (T)
Cytosine (C)
Guanine (G)
Adenine (A)
Pyrimidines
Purines
Thymine (T)
Cytosine (C)
Pyrimidines
Figure 10.2B_2
10.2 DNA and RNA are Polymers of Nucleotides
 RNA (ribonucleic acid) is unlike DNA in that it
– uses the sugar ribose (instead of deoxyribose in DNA)
and
– RNA has the nitrogenous base uracil (U) instead of
thymine.
Guanine (G)
Adenine (A)
Purines
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Figure 10.2C
Figure 10.2D
Nitrogenous base
(can be A, G, C, or U)
Phosphate
group
Cytosine
Uracil
Adenine
Guanine
Uracil (U)
Ribose
Phosphate
Sugar
(ribose)
5
10.3 SCIENTIFIC DISCOVERY: DNA is a
double-stranded helix
Figure 10.3A
 In 1952, after the Hershey-Chase experiment
demonstrated that the genetic material was most
likely DNA, a race was on to
– describe the structure of DNA and
– explain how the structure and properties of DNA can
account for its role in heredity.
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Figure 10.3A_1
Figure 10.3A_2
10.3 SCIENTIFIC DISCOVERY: DNA is a
double-stranded helix
10.3 SCIENTIFIC DISCOVERY: DNA is a
double-stranded helix
 In 1953, James D. Watson and Francis Crick
deduced the secondary structure of DNA, using
 Watson and Crick reported that DNA consisted of
two polynucleotide strands wrapped into a double
helix.
– X-ray crystallography data of DNA from the work of
Rosalind Franklin and Maurice Wilkins and
– Chargaff’s observation that in DNA,
– the amount of adenine was equal to the amount of thymine
and
– the amount of guanine was equal to that of cytosine.
– The sugar-phosphate backbone is on the outside.
– The nitrogenous bases are perpendicular to the
backbone in the interior.
– Specific pairs of bases give the helix a uniform shape.
– A pairs with T, forming two hydrogen bonds, and
– G pairs with C, forming three hydrogen bonds.
Animation: DNA Double Helix
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© 2012 Pearson Education, Inc.
6
Figure 10.3B
Figure 10.3C
Twist
Figure 10.3D
Figure 10.3D_1
C
C
G
Hydrogen bond
G
C
C
T
Base pair
G
G
Base pair
A
A
T
C
G
A
T
T
C
G
C
Computer
model
C
G
A
Partial chemical
structure
Ribbon
model
A
G
A
T
T
T
A
Ribbon
model
Figure 10.3D_2
Figure 10.3D_3
Hydrogen bond
G
T
C
A
A
C
T
G
Partial chemical
structure
Computer
model
7
10.3 SCIENTIFIC DISCOVERY: DNA is a
double-stranded helix
 In 1962, the Nobel Prize was awarded to
DNA REPLICATION
– James D. Watson, Francis Crick, and Maurice Wilkins.
– Rosalind Franklin probably would have received the
prize as well but for her death from cancer in 1958.
Nobel Prizes are never awarded posthumously.
 The Watson-Crick model gave new meaning to
the words genes and chromosomes. The genetic
information in a chromosome is encoded in the
nucleotide sequence of DNA.
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10.4 DNA replication depends on specific base
pairing
 In their description of the structure of DNA,
Watson and Crick noted that the structure of DNA
suggests a possible copying mechanism.
 DNA replication follows a semiconservative
model.
– The two DNA strands separate.
– Each strand is used as a pattern to produce a
complementary strand, using specific base pairing.
Figure 10.4A_s1
A
T
C
G
G
C
A
T
T
A
A parental
molecule
of DNA
– Each new DNA helix has one old strand with one new
strand.
Animation: DNA Replication Overview
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Figure 10.4A_s2
Figure 10.4A_s3
A
T
A
C
G
C
G
C
A
T
T
A
T
A parental
molecule
of DNA
T
A
T
A
T
A
T
G
C
G
C
G
C
G
C
A
T
A
T
A
T
A
T
A
T
A
G
C
G
C
G
C
G
C
G
C
A
T
A
T
A
T
T
A
T
A
T
G
C
Free
nucleotides
The parental strands
separate and serve
as templates
A
A parental
molecule
of DNA
G
C
Free
nucleotides
The parental strands
separate and serve
as templates
A
T
G
Two identical
daughter molecules
of DNA are formed
8
Figure 10.4B
A
G
A
A
T
10.5 DNA replication proceeds in two directions
at many sites simultaneously
T
C
T
T
A
Parental DNA
molecule
 DNA replication begins at the origins of replication
where
– DNA unwinds at the origin to produce a “bubble,”
Daughter
strand
Parental
strand
– replication proceeds in both directions from the origin,
and
– replication ends when products from the bubbles
merge with each other.
Daughter DNA
molecules
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10.5 DNA replication proceeds in two directions
at many sites simultaneously
10.5 DNA replication proceeds in two directions
at many sites simultaneously
 DNA replication occurs in the 5 to 3 direction.
 Two key proteins are involved in DNA replication.
– Replication is continuous on the 3 to 5 template.
1. DNA ligase joins small fragments into a continuous
chain.
– Replication is discontinuous on the 5 to 3 template,
forming short segments.
2. DNA polymerase
– adds nucleotides to a growing chain and
– proofreads and corrects improper base pairings.
Animation: Origins of Replication
Animation: Leading Strand
Animation: Lagging Strand
Animation: DNA Replication Review
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10.5 DNA replication proceeds in two directions
at many sites simultaneously
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Figure 10.5A
Parental
DNA
molecule
 DNA polymerases and DNA ligase also repair
DNA damaged by harmful radiation and toxic
chemicals.
 DNA replication ensures that all the somatic cells
in a multicellular organism carry the same genetic
information.
Origin of
replication
Parental strand
Daughter strand
“Bubble”
Two
daughter
DNA
molecules
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9
Figure 10.5B
Figure 10.5C
P
HO
5
4
3
2
1
T
3
4
1
5
C
G
G
C
P
Parental DNA
Replication fork
3
5
This daughter
strand is
synthesized
continuously
This daughter
strand is
3 synthesized
5 in pieces
P
P
P
5
3
P
T
3 end
5
3
2
A
P
OH
DNA polymerase
molecule
3 end
5 end
A
DNA ligase
P
5 end
THE FLOW OF GENETIC
INFORMATION FROM DNA TO
RNA TO PROTEIN
Overall direction of replication
10.6 The DNA genotype is expressed as proteins,
which provide the molecular basis for
phenotypic traits
 DNA specifies traits by dictating protein synthesis.
 The molecular chain of command is from
– DNA in the nucleus to RNA and
– RNA in the cytoplasm to protein.
 Transcription is the synthesis of RNA under the
direction of DNA.
 Translation is the synthesis of proteins under the
direction of RNA.
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Figure 10.6A_s1
Figure 10.6A_s2
DNA
DNA
Transcription
RNA
NUCLEUS
NUCLEUS
CYTOPLASM
CYTOPLASM
10
Figure 10.6A_s3
10.6 The DNA genotype is expressed as proteins,
which provide the molecular basis for
phenotypic traits
DNA
 The connections between genes and proteins
Transcription
– The initial one gene–one enzyme hypothesis was
based on studies of inherited metabolic diseases.
RNA
NUCLEUS
Translation
– The one gene–one enzyme hypothesis was expanded
to include all proteins.
CYTOPLASM
Protein
– Most recently, the one gene–one polypeptide
hypothesis recognizes that some proteins are
composed of multiple polypeptides.
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Figure 10.6B
10.7 Genetic information written in codons is
translated into amino acid sequences
 The sequence of nucleotides in DNA provides a
code for constructing a protein.
– Protein construction requires a conversion of a
nucleotide sequence to an amino acid sequence.
– Transcription rewrites the DNA code into RNA, using
the same nucleotide “language.”
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10.7 Genetic information written in codons is
translated into amino acid sequences
Figure 10.7
DNA
molecule
Gene 1
– The flow of information from gene to protein is based
on a triplet code: the genetic instructions for the
amino acid sequence of a polypeptide chain are written
in DNA and RNA as a series of nonoverlapping threebase “words” called codons.
– Translation involves switching from the nucleotide
“language” to the amino acid “language.”
– Each amino acid is specified by a codon.
– 64 codons are possible.
– Some amino acids have more than one possible codon.
Gene 2
Gene 3
DNA
A A A C C G G C A A A A
Transcription
RNA
Translation
U
U
U G G
C
C
G U
U
U U
Codon
Polypeptide
Amino
acid
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11
Figure 10.7_1
10.8 The genetic code dictates how codons are
translated into amino acids
DNA
A A
A C
U U
U
C G G
C
A
A
A A
C G U
U
U
 Characteristics of the genetic code
Transcription
RNA
Translation
– Three nucleotides specify one amino acid.
G
G C
– 61 codons correspond to amino acids.
U
– AUG codes for methionine and signals the start of
transcription.
Codon
– 3 “stop” codons signal the end of translation.
Polypeptide
Amino
acid
© 2012 Pearson Education, Inc.
Figure 10.8A
10.8 The genetic code dictates how codons are
translated into amino acids
Second base
 The genetic code is
First base
Third base
– redundant, with more than one codon for some amino
acids,
– unambiguous in that any codon for one amino acid
does not code for any other amino acid,
– nearly universal—the genetic code is shared by
organisms from the simplest bacteria to the most
complex plants and animals, and
– without punctuation in that codons are adjacent to each
other with no gaps in between.
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Figure 10.8B_s1
Figure 10.8B_s2
Strand to be transcribed
T A C T
T
Strand to be transcribed
C A A A A
T
T A C T
C
DNA
T
C A A A A
T
C
DNA
A T G A A G T
T T
A T G A A G T
T A G
T T
T A G
Transcription
RNA
A U G A A G U U U U A G
12
Figure 10.8B_s3
Figure 10.8C
Strand to be transcribed
T A C T
T
C A A A A
T
C
DNA
A T G A A G T
T T
T A G
Transcription
RNA
A U G A A G U U U U A G
Translation
Start
codon
Polypeptide
Met
Stop
codon
Lys
Phe
10.9 Transcription produces genetic messages in
the form of RNA
 Overview of transcription
– An RNA molecule is transcribed from a DNA template
by a process that resembles the synthesis of a DNA
strand during DNA replication.
– RNA nucleotides are linked by the transcription
enzyme RNA polymerase.
– Specific sequences of nucleotides along the DNA mark
where transcription begins and ends.
– The “start transcribing” signal is a nucleotide sequence
called a promoter.
10.9 Transcription produces genetic messages in
the form of RNA
– Transcription begins with initiation, as the RNA
polymerase attaches to the promoter.
– During the second phase, elongation, the RNA grows
longer.
– As the RNA peels away, the DNA strands rejoin.
– Finally, in the third phase, termination, the RNA
polymerase reaches a sequence of bases in the DNA
template called a terminator, which signals the end of
the gene.
– The polymerase molecule now detaches from the RNA
molecule and the gene.
Animation: Transcription
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© 2012 Pearson Education, Inc.
Figure 10.9A
Figure 10.9B
RNA polymerase
Free RNA
nucleotides
RNA
polymerase
DNA of gene
Terminator
DNA
Promoter
DNA
1
Initiation
2
Elongation
Area shown
in Figure 10.9A
3
Termination
Growing
RNA
C C A A
A U C C A
T A G G T
Direction of
transcription
Newly made RNA
T
Template
strand of DNA
Completed
RNA
RNA
polymerase
13
Figure 10.9B_1
Figure 10.9B_2
RNA polymerase
Terminator
DNA
DNA of gene
2
Promoter
DNA
1
Elongation
Area shown
in Figure 10.9A
Initiation
Growing
RNA
Figure 10.9B_3
10.10 Eukaryotic RNA is processed before
leaving the nucleus as mRNA
 Messenger RNA (mRNA)
– encodes amino acid sequences and
3
Termination
Growing
RNA
– conveys genetic messages from DNA to the translation
machinery of the cell, which in
– prokaryotes, occurs in the same place that mRNA is made,
but in
– eukaryotes, mRNA must exit the nucleus via nuclear pores to
enter the cytoplasm.
– Eukaryotic mRNA has
Completed
RNA
– introns, interrupting sequences that separate
RNA
polymerase
– exons, the coding regions.
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10.10 Eukaryotic RNA is processed before
leaving the nucleus as mRNA
Figure 10.10
Exon Intron
Cap
 Eukaryotic mRNA undergoes processing before
leaving the nucleus.
– RNA splicing removes introns and joins exons to
produce a continuous coding sequence.
– A cap and tail of extra nucleotides are added to the
ends of the mRNA to
– facilitate the export of the mRNA from the nucleus,
– protect the mRNA from attack by cellular enzymes, and
Exon
Intron
Exon
DNA
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
NUCLEUS
– help ribosomes bind to the mRNA.
CYTOPLASM
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14
10.11 Transfer RNA molecules serve as
interpreters during translation
Figure 10.11A
Amino acid
attachment site
 Transfer RNA (tRNA) molecules function as a
language interpreter,
– converting the genetic message of mRNA
Hydrogen bond
– into the language of proteins.
 Transfer RNA molecules perform this interpreter
task by
RNA polynucleotide
chain
– picking up the appropriate amino acid and
– using a special triplet of bases, called an anticodon, to
recognize the appropriate codons in the mRNA.
Anticodon
A tRNA molecule, showing
its polynucleotide strand
and hydrogen bonding
A simplified
schematic of a tRNA
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Figure 10.11B
10.12 Ribosomes build polypeptides
Enzyme
tRNA
 Translation occurs on the surface of the ribosome.
ATP
– Ribosomes coordinate the functioning of mRNA and
tRNA and, ultimately, the synthesis of polypeptides.
– Ribosomes have two subunits: small and large.
– Each subunit is composed of ribosomal RNAs and
proteins.
– Ribosomal subunits come together during translation.
– Ribosomes have binding sites for mRNA and tRNAs.
© 2012 Pearson Education, Inc.
Figure 10.12A
Figure 10.12B
Growing
polypeptide
tRNA
molecules
tRNA binding sites
Large
subunit
Small
subunit
Large
subunit
P A
site site
Small
subunit
mRNA binding site
mRNA
15
Figure 10.12C
10.13 An initiation codon marks the start of an
mRNA message
 Translation can be divided into the same three
phases as transcription:
The next amino
acid to be added
to the polypeptide
Growing
polypeptide
1. initiation,
mRNA
tRNA
2. elongation, and
3. termination.
 Initiation brings together
Codons
– mRNA,
– a tRNA bearing the first amino acid, and
– the two subunits of a ribosome.
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10.13 An initiation codon marks the start of an
mRNA message
 Initiation establishes where translation will begin.
Figure 10.13A
Start of genetic message
Cap
 Initiation occurs in two steps.
1. An mRNA molecule binds to a small ribosomal subunit and
the first tRNA binds to mRNA at the start codon.
– The start codon reads AUG and codes for methionine.
– The first tRNA has the anticodon UAC.
End
2. A large ribosomal subunit joins the small subunit, allowing
the ribosome to function.
Tail
– The first tRNA occupies the P site, which will hold the growing
peptide chain.
– The A site is available to receive the next tRNA.
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Figure 10.13B
10.14 Elongation adds amino acids to the
polypeptide chain until a stop codon
terminates translation
Large
ribosomal
subunit
Initiator
tRNA
P
site
mRNA
U A C
A U G
A
site
U A C
A U G
 Once initiation is complete, amino acids are
added one by one to the first amino acid.
 Elongation is the addition of amino acids to the
polypeptide chain.
Start codon
1
Small
ribosomal
subunit
2
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16
10.14 Elongation adds amino acids to the
polypeptide chain until a stop codon
terminates translation
10.14 Elongation adds amino acids to the
polypeptide chain until a stop codon
terminates translation
 Each cycle of elongation has three steps.
 Elongation continues until the termination stage of
translation, when
1. Codon recognition: The anticodon of an incoming
tRNA molecule, carrying its amino acid, pairs with the
mRNA codon in the A site of the ribosome.
2. Peptide bond formation: The new amino acid is
joined to the chain.
– the ribosome reaches a stop codon,
– the completed polypeptide is freed from the last tRNA,
and
– the ribosome splits back into its separate subunits.
3. Translocation: tRNA is released from the P site and
the ribosome moves tRNA from the A site into the P
site.
Animation: Translation
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© 2012 Pearson Education, Inc.
Figure 10.14_s1
Figure 10.14_s2
Polypeptide
P
site
mRNA
Amino
acid
A
site
Polypeptide
P
site
Anticodon
Codons
1
mRNA
Amino
acid
A
site
Anticodon
Codons
1
Codon recognition
Codon recognition
2
Figure 10.14_s3
Peptide bond
formation
Figure 10.14_s4
Polypeptide
P
site
mRNA
Amino
acid
A
site
Polypeptide
P
site
Anticodon
Codons
1
mRNA
Amino
acid
A
site
Anticodon
Codons
1
Codon recognition
Codon recognition
mRNA
movement
Stop
codon
2
New
peptide
bond
3
Translocation
Peptide bond
formation
2
New
peptide
bond
3
Peptide bond
formation
Translocation
17
10.15 Review: The flow of genetic information in
the cell is DNA  RNA  protein
10.15 Review: The flow of genetic information in
the cell is DNA  RNA  protein
 Transcription is the synthesis of RNA from a DNA
template. In eukaryotic cells,
 Translation can be divided into four steps, all of
which occur in the cytoplasm:
– transcription occurs in the nucleus and
1. amino acid attachment,
– the mRNA must travel from the nucleus to the cytoplasm.
2. initiation of polypeptide synthesis,
3. elongation, and
4. termination.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Figure 10.15
Figure 10.15_1
Transcription
DNA
1
mRNA
Transcription
RNA
polymerase
CYTOPLASM
Translation
Amino acid
2 Amino acid
attachment
Enzyme
Transcription
tRNA
ATP
DNA
Anticodon
Initiator
tRNA
Large
ribosomal
subunit
Start Codon
3 Initiation of
polypeptide synthesis
Small
ribosomal
subunit
mRNA
1
mRNA
New peptide
bond forming
Growing
polypeptide
4
Elongation
5
Termination
Transcription
RNA
polymerase
Codons
mRNA
Polypeptide
Stop codon
Figure 10.15_2
Figure 10.15_3
CYTOPLASM
Translation
Amino acid
Amino acid
attachment
2
New peptide
bond forming
Growing
polypeptide
Enzyme
4
Elongation
tRNA
ATP
Codons
mRNA
Anticodon
Initiator
tRNA
Large
ribosomal
subunit
Start Codon
mRNA
Initiation of
polypeptide synthesis
Polypeptide
2 3
5
Small
ribosomal
subunit
Termination
Stop codon
18
10.16 Mutations can change the meaning of genes
10.16 Mutations can change the meaning of genes
 A mutation is any change in the nucleotide
sequence of DNA.
 Mutations within a gene can be divided into two
general categories.
 Mutations can involve
1. Base substitutions involve the replacement of one
nucleotide with another. Base substitutions may
– large chromosomal regions or
– have no effect at all, producing a silent mutation,
– just a single nucleotide pair.
– change the amino acid coding, producing a missense
mutation, which produces a different amino acid,
– lead to a base substitution that produces an improved protein
that enhances the success of the mutant organism and its
descendant, or
– change an amino acid into a stop codon, producing a
nonsense mutation.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
10.16 Mutations can change the meaning of genes
10.16 Mutations can change the meaning of genes
2. Mutations can result in deletions or insertions that may
– alter the reading frame (triplet grouping) of the mRNA, so that
nucleotides are grouped into different codons,
 Mutagenesis is the production of mutations.
 Mutations can be caused by
– lead to significant changes in amino acid sequence
downstream of the mutation, and
– spontaneous errors that occur during DNA replication
or recombination or
– produce a nonfunctional polypeptide.
– mutagens, which include
– high-energy radiation such as X-rays and
ultraviolet light and
– chemicals.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Figure 10.16A
Figure 10.16B
Normal
gene
mRNA
Protein
Normal hemoglobin DNA
C T
A
U G A
Met
Lys
U
U G G C G
C
Phe
Gly
Ala
A
Mutant hemoglobin DNA
C A T
T
Nucleotide
substitution
A U G A
Met
mRNA
A G U
U A G C
A G U U
Lys
Phe
Ser
G C
A
Ala
mRNA
U Deleted
G A A
G U A
Normal hemoglobin
Sickle-cell hemoglobin
Val
Glu
Nucleotide
deletion
A U G A
Met
A G
U
Lys
U G G C G
Ala
Leu
C A
U
His
Inserted
Nucleotide
insertion
A U G A
Met
A G
Lys
U
U G
Leu
U G G
C G C
Ala
His
19
10.17 Viral DNA may become part of the host
chromosome
THE GENETICS OF VIRUSES
AND BACTERIA
 A virus is essentially “genes in a box,” an
infectious particle consisting of
– a bit of nucleic acid,
– wrapped in a protein coat called a capsid, and
– in some cases, a membrane envelope.
 Viruses have two types of reproductive cycles.
1. In the lytic cycle,
– viral particles are produced using host cell components,
– the host cell lyses, and
– viruses are released.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
10.17 Viral DNA may become part of the host
chromosome
Figure 10.17_s1
Phage
Attaches
to cell
Phage DNA
2. In the Lysogenic cycle
– Viral DNA is inserted into the host chromosome by
recombination.
4
The cell lyses,
releasing
phages
1
– Viral DNA is duplicated along with the host chromosome during
each cell division.
Bacterial
chromosome
The phage injects its DNA
– The inserted phage DNA is called a prophage.
Lytic cycle
– Most prophage genes are inactive.
Phages assemble
2
– Environmental signals can cause a switch to the lytic cycle,
causing the viral DNA to be excised from the bacterial
chromosome and leading to the death of the host cell.
3
Animation: Phage Lambda Lysogenic and Lytic Cycles
The phage DNA
circularizes
New phage DNA and
proteins are synthesized
Animation: Phage T4 Lytic Cycle
© 2012 Pearson Education, Inc.
Figure 10.17_s2
Figure 10.17_1
Phage
Attaches
to cell
Phage DNA
Phage
Attaches
to cell
Phage DNA
4
The cell lyses,
releasing
phages
1
Bacterial
chromosome
The cell lyses,
releasing
phages
Lytic cycle
Environmental
stress
The phage injects its DNA
Many cell
divisions
Lysogenic cycle
2
The phage DNA
circularizes
Prophage
6
The lysogenic bacterium
replicates normally
Lytic cycle
Phages assemble
2
OR
3
1
Bacterial
chromosome
The phage injects its DNA
7
Phages assemble
4
New phage DNA and
proteins are synthesized
5
The phage DNA
circularizes
Phage DNA inserts into the bacterial
chromosome by recombination
3
New phage DNA and
proteins are synthesized
20
Figure 10.17_2
10.18 CONNECTION: Many viruses cause
disease in animals and plants
Phage
Attaches
to cell
Bacterial
chromosome
Phage DNA
1
 Viruses can cause disease in animals and plants.
The phage injects its DNA
Environmental
stress
7
Many cell
divisions
Lysogenic cycle
2
The phage DNA
circularizes
6
Prophage
The lysogenic bacterium
replicates normally, copying the
prophage at each cell division
Phage DNA inserts into the bacterial
chromosome by recombination
5
 DNA viruses and RNA viruses cause disease in
animals.
 A typical animal virus has a membranous outer
envelope and projecting spikes of glycoprotein.
 The envelope helps the virus enter and leave the
host cell.
 Many animal viruses have RNA rather than DNA as
their genetic material. These include viruses that
cause the common cold, measles, mumps, polio,
and AIDS.
© 2012 Pearson Education, Inc.
10.18 CONNECTION: Many viruses cause
disease in animals and plants
10.18 CONNECTION: Many viruses cause
disease in animals and plants
 The reproductive cycle of the mumps virus, a typical
enveloped RNA virus, has seven major steps:
 Some animal viruses, such as herpesviruses,
reproduce in the cell nucleus.
1.
2.
3.
4.
5.
entry of the protein-coated RNA into the cell,
uncoating—the removal of the protein coat,
RNA synthesis—mRNA synthesis using a viral enzyme,
protein synthesis—mRNA is used to make viral proteins,
new viral genome production—mRNA is used as a
template to synthesize new viral genomes,
6. assembly—the new coat proteins assemble around the
new viral RNA, and
7. exit—the viruses leave the cell by cloaking themselves in
the host cell’s plasma membrane.
© 2012 Pearson Education, Inc.
 Most plant viruses are RNA viruses.
– To infect a plant, they must get past the outer protective
layer of the plant.
– Viruses spread from cell to cell through plasmodesmata.
– Infection can spread to other plants by insects,
herbivores, humans, or farming tools.
 There are no cures for most viral diseases of plants
or animals.
Animation: Simplified Viral Reproductive Cycle
© 2012 Pearson Education, Inc.
Figure 10.18
Figure 10.18_1
Glycoprotein spike
Protein coat
Plasma
membrane
of host cell
1
Entry
2
Uncoating
3
RNA synthesis
by viral enzyme
Protein coat
CYTOPLASM
Protein
synthesis
5
mRNA
RNA synthesis
(other strand)
Template
Plasma
membrane
of host cell
New viral
genome
New
viral proteins
Membranous
envelope
Viral RNA (genome)
Viral RNA
(genome)
4
Glycoprotein spike
Membranous
envelope
Viral RNA (genome)
6
Assembly
CYTOPLASM
1
Entry
2
Uncoating
3
RNA synthesis
by viral enzyme
Viral RNA
(genome)
Exit
7
21
Figure 10.18_2
4
Protein
synthesis
5
mRNA
RNA synthesis
(other strand)
Template
New viral
genome
New
viral proteins
6
Assembly
10.19 EVOLUTION CONNECTION: Emerging
viruses threaten human health
 Viruses that appear suddenly or are new to medical
scientists are called emerging viruses. These
include the
– AIDS virus,
– Ebola virus,
– West Nile virus, and
– SARS virus.
Exit
7
© 2012 Pearson Education, Inc.
10.19 EVOLUTION CONNECTION: Emerging
viruses threaten human health
Figure 10.19
 Three processes contribute to the emergence of
viral diseases:
1. mutation—RNA viruses mutate rapidly.
2. contact between species—viruses from other animals
spread to humans.
3. spread from isolated human populations to larger human
populations, often over great distances.
© 2012 Pearson Education, Inc.
Figure 10.19_1
Figure 10.19_2
22
10.20 The AIDS virus makes DNA on an RNA
template
Figure 10.20A
 AIDS (acquired immunodeficiency syndrome) is
caused by HIV (human immunodeficiency virus).
Envelope
Glycoprotein
 HIV
Protein coat
RNA
(two identical
strands)
– is an RNA virus,
– has two copies of its RNA genome,
Reverse
transcriptase
(two copies)
– carries molecules of reverse transcriptase, which
causes reverse transcription, producing DNA from an
RNA template.
© 2012 Pearson Education, Inc.
10.20 The AIDS virus makes DNA on an RNA
template
 After HIV RNA is uncoated in the cytoplasm of the
host cell,
1. reverse transcriptase makes one DNA strand from RNA,
2. reverse transcriptase adds a complementary DNA strand,
3. double-stranded viral DNA enters the nucleus and
integrates into the chromosome, becoming a provirus,
4. the provirus DNA is used to produce mRNA,
Figure 10.20B
Reverse
transcriptase
Viral RNA
1
DNA
strand
CYTOPLASM
NUCLEUS
Chromosomal
DNA
2
Doublestranded
DNA
3
Provirus
DNA
4
5
Viral
RNA
and
proteins
RNA
6
5. the viral mRNA is translated to produce viral proteins, and
6. new viral particles are assembled, leave the host cell, and
can then infect other cells.
Animation: HIV Reproductive Cycle
© 2012 Pearson Education, Inc.
10.21 Viroids and prions are formidable
pathogens in plants and animals
10.22 Bacteria can transfer DNA in three ways
 Some infectious agents are made only of RNA or
protein.
 Viral reproduction allows researchers to learn more
about the mechanisms that regulate DNA replication
and gene expression in living cells.
– Viroids are small, circular RNA molecules that infect
plants. Viroids
– replicate within host cells without producing proteins and
– interfere with plant growth.
– Prions are infectious proteins that cause degenerative
brain diseases in animals. Prions
– appear to be misfolded forms of normal brain proteins,
– which convert normal protein to misfolded form.
© 2012 Pearson Education, Inc.
 Bacteria are also valuable but for different reasons.
– Bacterial DNA is found in a single, closed loop,
chromosome.
– Bacterial cells divide by replication of the bacterial
chromosome and then by binary fission.
– Because binary fission is an asexual process, bacteria in
a colony are genetically identical to the parent cell.
© 2012 Pearson Education, Inc.
23
10.22 Bacteria can transfer DNA in three ways
Figure 10.22A
 Bacteria use three mechanisms to move genes from
cell to cell.
DNA enters
cell
1. Transformation is the uptake of DNA from the surrounding
environment.
A fragment of
DNA from
another
bacterial cell
2. Transduction is gene transfer by phages.
3. Conjugation is the transfer of DNA from a donor to a
recipient bacterial cell through a cytoplasmic (mating)
bridge.
Bacterial chromosome
(DNA)
 Once new DNA gets into a bacterial cell, part of it may
then integrate into the recipient’s chromosome.
© 2012 Pearson Education, Inc.
Figure 10.22B
Figure 10.22C
Mating bridge
Phage
Sex pili
A fragment
of DNA from
another
bacterial cell
(former phage host)
Donor cell
Figure 10.22D
Recipient cell
10.23 Bacterial plasmids can serve as carriers for
gene transfer
Donated DNA
Recipient cell’s
chromosome
Crossovers
Degraded DNA
Recombinant
chromosome
 The ability of a donor E. coli cell to carry out
conjugation is usually due to a specific piece of DNA
called the F factor.
 During conjugation, the F factor is integrated into the
bacterium’s chromosome.
 The donor chromosome starts replicating at the F
factor’s origin of replication.
 The growing copy of the DNA peels off and heads
into the recipient cell.
 The F factor serves as the leading end of the
transferred DNA.
© 2012 Pearson Education, Inc.
24
Figure 10.23A-B
Figure 10.23A
F factor
(integrated)
F factor
(integrated)
F factor (plasmid)
Donor
Donor
Origin of F
replication
Bacterial
chromosome
F factor starts
replication and transfer
of chromosome
Donor
Origin of F
replication
Bacterial
chromosome
Bacterial
chromosome
F factor starts
replication and transfer
F factor starts
replication and transfer
of chromosome
Recipient
cell
Only part of the
chromosome transfers
Recombination
can occur
Recipient
cell
The plasmid completes its
transfer and circularizes
Only part of the
chromosome transfers
The cell is
now a donor
10.23 Bacterial plasmids can serve as carriers for
gene transfer
Recombination
can occur
Figure 10.23B
F factor (plasmid)
Donor
Bacterial
chromosome
 An F factor can also exist as a plasmid, a small
circular DNA molecule separate from the bacterial
chromosome.
F factor starts
replication and transfer
– Some plasmids, including the F factor, can bring about
conjugation and move to another cell in linear form.
– The transferred plasmid re-forms a circle in the recipient
cell.
The plasmid completes its
transfer and circularizes
 R plasmids
– pose serious problems for human medicine by
The cell is
now a donor
– carrying genes for enzymes that destroy antibiotics.
© 2012 Pearson Education, Inc.
Figure 10.23C
You should now be able to
Plasmids
1. Describe the experiments of Griffith, Hershey,
and Chase, which supported the idea that DNA
was life’s genetic material.
2. Compare the structures of DNA and RNA.
3. Explain how the structure of DNA facilitates its
replication.
4. Describe the process of DNA replication.
5. Describe the locations, reactants, and products of
transcription and translation.
© 2012 Pearson Education, Inc.
25
You should now be able to
You should now be able to
6. Explain how the “languages” of DNA and RNA
are used to produce polypeptides.
11. Describe the step-by-step process by which amino
acids are added to a growing polypeptide chain.
7. Explain how mRNA is produced using DNA.
12. Diagram the overall process of transcription and
translation.
8. Explain how eukaryotic RNA is processed
before leaving the nucleus.
9. Relate the structure of tRNA to its functions in
the process of translation.
10. Describe the structure and function of
ribosomes.
© 2012 Pearson Education, Inc.
13. Describe the major types of mutations, causes of
mutations, and potential consequences.
14. Compare the lytic and lysogenic reproductive
cycles of a phage.
15. Compare the structures and reproductive cycles of
the mumps virus and a herpesvirus.
© 2012 Pearson Education, Inc.
Figure 10.UN01
You should now be able to
Sugarphosphate
backbone
16. Describe three processes that contribute to the
emergence of viral disease.
Nitrogenous base
G
Phosphate
group
A
17. Explain how the AIDS virus enters a host cell and
reproduces.
C
18. Describe the structure of viroids and prions and
explain how they cause disease.
T
19. Define and compare the processes of
transformation, transduction, and conjugation.
20. Define a plasmid and explain why R plasmids
pose serious human health problems.
Sugar
Nucleotide
Nitrogenous
bases
G
RNA
C
G
A
T
C
G
A
U
DeoxyRibose
ribose
Sugar
Polynucleotide
DNA
DNA
© 2012 Pearson Education, Inc.
Figure 10.UN02
Figure 10.UN03
DNA
Growing polypeptide
Large
ribosomal
subunit
is a polymer
made from
monomers called
is performed
by an
enzyme called
(b)
(a)
(c)
Amino acid
(d)
tRNA
RNA
comes
in three
kinds called
Anticodon
mRNA
Codons
Small
ribosomal
subunit
(e)
(f)
(g)
is performed
by structures
called
Protein
molecules are
components of
use amino-acid-bearing
molecules called
(h)
one or more polymers
made from
monomers called
(i)
26
Figure 10.1_UN
Figure 10.17_UN
Figure 10.18_UN
27