Download DNA

Chapter 10
The Structure and Function of DNA
PowerPoint® Lectures for
Campbell Essential Biology, Fifth Edition, and
Campbell Essential Biology with Physiology,
Fourth Edition
– Eric J. Simon, Jean L. Dickey, and Jane B. Reece
Lectures by Edward J. Zalisko
© 2013 Pearson Education, Inc.
Biology and Society:
Mix-and-Match Viruses
• In 2009, a cluster of unusual flu cases broke out
around Mexico City.
• In June 2009, the World Health Organization
(WHO)
– declared H1N1 a pandemic (global epidemic) and
– unveiled a massive effort to contain it.
• Scientists soon determined that H1N1 was a hybrid
flu strain, made when a known flu virus mixed with
an Asian swine flu virus.
© 2013 Pearson Education, Inc.
Biology and Society:
Mix-and-Match Viruses
• The hybrid H1N1 flu strain had a combination of
genes that infected young, healthy people instead
of the elderly or people who were already sick.
• Many countries produced a coordinated response,
and the WHO declared the pandemic over in
August 2010.
© 2013 Pearson Education, Inc.
Biology and Society:
Mix-and-Match Viruses
• Each year in the United States, over 20,000 people
die from influenza infection.
• From 1918 to 1919, the deadliest pandemic killed
about 40 million people worldwide in just 18
months.
© 2013 Pearson Education, Inc.
DNA: STRUCTURE AND REPLICATION
• DNA
– was known to be a chemical in cells by the end of
the nineteenth century,
– has the capacity to store genetic information, and
– can be copied and passed from generation to
generation.
• The discovery of DNA as the hereditary material
ushered in the new field of molecular biology, the
study of heredity at the molecular level.
© 2013 Pearson Education, Inc.
DNA and RNA Structure
• DNA and RNA are nucleic acids.
– They consist of chemical units called nucleotides.
– A nucleotide polymer is a polynucleotide.
– Nucleotides are joined by covalent bonds between
the sugar of one nucleotide and the phosphate of
the next, forming a sugar-phosphate backbone.
Animation: DNA and RNA Structure
Animation: Hershey-Chase Experiment
© 2013 Pearson Education, Inc.
Figure 10.1
Phosphate
group
Nitrogenous base
Sugar
DNA
nucleotide
DNA
double
helix
Nitrogenous base
(can be A, G, C, or T)
Thymine (T)
Phosphate
group
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate
backbone
Figure 10.1a
Phosphate
group
Nitrogenous base
Sugar
DNA
nucleotide
Nitrogenous base
(can be A, G, C, or T)
Thymine (T)
Phosphate
group
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate
backbone
Figure 10.1b
Nitrogenous base
(can be A, G, C, or T)
Thymine (T)
Phosphate
group
Sugar
(deoxyribose)
DNA nucleotide
DNA and RNA Structure
• The sugar in DNA is deoxyribose. Thus, the full
name for DNA is deoxyribonucleic acid.
© 2013 Pearson Education, Inc.
DNA and RNA Structure
• The four nucleotides found in DNA differ in their
nitrogenous bases. These bases are
– thymine (T),
– cytosine (C),
– adenine (A), and
– guanine (G).
• RNA has uracil (U) in place of thymine.
© 2013 Pearson Education, Inc.
Figure 10.2
Cytosine
Uracil
Adenine
Guanine
Phosphate
Sugar
(ribose)
Watson and Crick’s Discovery of the Double Helix
• James Watson and Francis Crick determined that
DNA is a double helix.
• Watson and Crick used X-ray crystallography data
to reveal the basic shape of DNA.
• Rosalind Franklin produced the X-ray image of
DNA.
© 2013 Pearson Education, Inc.
Figure 10.3a
James Watson (left) and Francis Crick
Figure 10.3b
Rosalind Franklin
X-ray images of DNA
Watson and Crick’s Discovery of the Double Helix
• The model of DNA is like a rope ladder twisted into
a spiral.
– The ropes at the sides represent the sugarphosphate backbones.
– Each wooden rung represents a pair of bases
connected by hydrogen bonds.
© 2013 Pearson Education, Inc.
Figure 10.4
Twist
Watson and Crick’s Discovery of the Double Helix
• DNA bases pair in a complementary fashion:
– adenine (A) pairs with thymine (T) and
– cytosine (C) pairs with guanine (G).
Blast Animation: Structure of DNA Double Helix
Blast Animation: Hydrogen Bonds in DNA
Animation: DNA Double Helix
© 2013 Pearson Education, Inc.
Figure 10.5
Hydrogen bond
(a) Ribbon model
(b) Atomic model
(c) Computer model
Figure 10.5a
(a) Ribbon model
Figure 10.5b
Hydrogen bond
(b) Atomic model
DNA Replication
• When a cell reproduces, a complete copy of the
DNA must pass from one generation to the next.
• Watson and Crick’s model for DNA suggested that
DNA replicates by a template mechanism.
Bioflix Animation: DNA Replication
Animation: DNA Replication Overview
Animation: DNA Replication Review
© 2013 Pearson Education, Inc.
Figure 10.6
Parental (old)
DNA molecule
Daughter
(new) strand
Parental
(old) strand
Daughter DNA
molecules
(double helices)
DNA Replication
• DNA can be damaged by X-rays and ultraviolet
light.
• DNA polymerases
– are enzymes,
– make the covalent bonds between the nucleotides
of a new DNA strand, and
– are involved in repairing damaged DNA.
© 2013 Pearson Education, Inc.
DNA Replication
• DNA replication ensures that all the body cells in
multicellular organisms carry the same genetic
information.
© 2013 Pearson Education, Inc.
DNA Replication
• DNA replication in eukaryotes
– begins at specific sites on a double helix (called
origins of replication) and
– proceeds in both directions.
Animation: Origins of Replication
Animation: Leading Strand
Animation: Lagging Strand
© 2013 Pearson Education, Inc.
Figure 10.7
Origin of
replication
Origin of
replication
Parental strands
Origin of
replication
Parental strand
Daughter strand
Bubble
Two daughter DNA molecules
THE FLOW OF GENETIC INFORMATION
FROM DNA TO RNA TO PROTEIN
• DNA provides instructions to
– a cell and
– an organism as a whole.
© 2013 Pearson Education, Inc.
How an Organism’s Genotype Determines Its
Phenotype
• An organism’s genotype is its genetic makeup, the
sequence of nucleotide bases in DNA.
• The phenotype is the organism’s physical traits,
which arise from the actions of a wide variety of
proteins.
© 2013 Pearson Education, Inc.
How an Organism’s Genotype Determines Its
Phenotype
• DNA specifies the synthesis of proteins in two
stages:
1. transcription, the transfer of genetic information
from DNA into an RNA molecule and
2. translation, the transfer of information from RNA
into a protein.
Bioflix Animation: Protein Synthesis
© 2013 Pearson Education, Inc.
Figure 10.8-3
DNA
TRANSCRIPTION
Nucleus
RNA
Cytoplasm
TRANSLATION
Protein
How an Organism’s Genotype Determines Its
Phenotype
• The major breakthrough in demonstrating the
relationship between genes and enzymes came in
the 1940s from the work of American geneticists
George Beadle and Edward Tatum with the bread
mold Neurospora crassa.
© 2013 Pearson Education, Inc.
How an Organism’s Genotype Determines Its
Phenotype
• Beadle and Tatum
– studied strains of mold that were unable to grow on
the usual growth medium,
– determined that these strains lacked an enzyme in
a metabolic pathway that synthesized arginine,
– showed that each mutant was defective in a single
gene, and
– hypothesized that the function of an individual gene
is to dictate the production of a specific enzyme.
© 2013 Pearson Education, Inc.
How an Organism’s Genotype Determines Its
Phenotype
• The one gene–one enzyme hypothesis has since
been modified.
• The function of a gene is to dictate the production
of a polypeptide.
• A protein may consist of two or more different
polypeptides.
© 2013 Pearson Education, Inc.
From Nucleotides to Amino Acids: An Overview
• Genetic information in DNA is
– transcribed into RNA, then
– translated into polypeptides,
– which then fold into proteins.
© 2013 Pearson Education, Inc.
From Nucleotides to Amino Acids: An Overview
• What is the language of nucleic acids?
– In DNA, it is the linear sequence of nucleotide
bases.
– A typical gene consists of thousands of nucleotides
in a specific sequence.
• When a segment of DNA is transcribed, the result
is an RNA molecule.
• RNA is then translated into a sequence of amino
acids in a polypeptide.
© 2013 Pearson Education, Inc.
Figure 10.10
Gene 1
Gene 2
DNA molecule
Gene 3
DNA strand
TRANSCRIPTION
RNA
TRANSLATION
Codon
Polypeptide
Amino acid
Figure 10.10a
DNA strand
TRANSCRIPTION
RNA
TRANSLATION
Codon
Polypeptide
Amino acid
From Nucleotides to Amino Acids: An Overview
• Experiments have verified that the flow of
information from gene to protein is based on a
triplet code.
• A codon is a triplet of bases, which codes for one
amino acid.
© 2013 Pearson Education, Inc.
The Genetic Code
• The genetic code is the set of rules that convert a
nucleotide sequence in RNA to an amino acid
sequence.
• Of the 64 triplets,
– 61 code for amino acids and
– 3 are stop codons, instructing the ribosomes to end
the polypeptide.
© 2013 Pearson Education, Inc.
Figure 10.11
Second base of RNA codon
UUU
U
UUC
UUA
UUG
UCU
Phenylalanine
UCC
(Phe)
Leucine
(Leu)
First base of RNA codon
CUU
C
CUC
CUA
A
Leucine
(Leu)
A
UAU
UGA Stop
UCG
UAG
Stop
UGG Tryptophan (Trp) G
CCU
CAU
CCC
CCA
Proline
(Pro)
CAC
CAA
ACU
AAU
ACC
ACA
AAC
Threonine
(Thr)
AAA
ACG
AAG
GCU
GAU
Met or start
GUU
GUC
GUA
GUG
Valine
(Val)
U
Stop
AUU
AUG
Cysteine
(Cys)
UAA
UCA
CAG
Isoleucine
(Ile)
UGU
UAC
Serine
(Ser)
CCG
AUC
G
Tyrosine
(Tyr)
CUG
AUA
G
C
GCC
GCA
GCG
Alanine
(Ala)
GAC
GAA
GAG
Histidine
(His)
Glutamine
(Gln)
UGC
CGU
CGC
CGA
Lysine
(Lys)
Aspartic
acid (Asp)
Glutamic
acid (Glu)
AGA
AGG
Arginine
(Arg)
GGA
GGG
C
A
G
Serine
(Ser)
Arginine
(Arg)
GGU
GGC
A
U
CGG
AGU
Asparagine
AGC
(Asn)
C
U
C
A
G
U
Glycine
(Gly)
C
A
G
Third base of RNA codon
U
The Genetic Code
• Because diverse organisms share a common
genetic code, it is possible to program one species
to produce a protein from another species by
transplanting DNA.
© 2013 Pearson Education, Inc.
Figure 10.12
Transcription: From DNA to RNA
• Transcription
– makes RNA from a DNA template,
– uses a process that resembles the synthesis of a
DNA strand during DNA replication, and
– substitutes uracil (U) for thymine (T).
© 2013 Pearson Education, Inc.
Transcription: From DNA to RNA
• RNA nucleotides are linked by the transcription
enzyme RNA polymerase.
Animation: Transcription
Blast Animation: Transcription
© 2013 Pearson Education, Inc.
Figure 10.13
RNA polymerase
DNA of gene
Promoter
DNA
1 Initiation
RNA
Terminator
DNA
2 Elongation
RNA nucleotides
RNA polymerase
3 Termination
Growing RNA
Newly
made
RNA
Direction of
transcription
Completed RNA
Template
strand of DNA
(a) A close-up view of transcription
RNA
polymerase
(b) Transcription of a gene
Figure 10.13a
RNA
polymerase
Newly
made
RNA
RNA nucleotides
Direction of
transcription
Template
strand of DNA
(a) A close-up view of transcription
Figure 10.13b
RNA polymerase
DNA of gene
Promoter
DNA
1
Initiation
RNA
Terminator DNA
2
3 Termination
Elongation
Growing RNA
Completed RNA
RNA polymerase
(b) Transcription of a gene
Initiation of Transcription
• The “start transcribing” signal is a nucleotide
sequence called a promoter, which is
– located in the DNA at the beginning of the gene
and
– a specific place where RNA polymerase attaches.
• The first phase of transcription is initiation, in which
– RNA polymerase attaches to the promoter and
– RNA synthesis begins.
© 2013 Pearson Education, Inc.
RNA Elongation
• During the second phase of transcription, called
elongation,
– the RNA grows longer and
– the RNA strand peels away from its DNA template.
© 2013 Pearson Education, Inc.
Termination of Transcription
• During the third phase of transcription, called
termination,
– RNA polymerase reaches a special sequence of
bases in the DNA template called a terminator,
signaling the end of the gene,
– polymerase detaches from the RNA and the gene,
and
– the DNA strands rejoin.
© 2013 Pearson Education, Inc.
The Processing of Eukaryotic RNA
• In the cells of prokaryotes, RNA transcribed from a
gene immediately functions as messenger RNA
(mRNA), the molecule that is translated into
protein.
• The eukaryotic cell
– localizes transcription in the nucleus and
– modifies, or processes, the RNA transcripts in the
nucleus before they move to the cytoplasm for
translation by ribosomes.
© 2013 Pearson Education, Inc.
The Processing of Eukaryotic RNA
• RNA processing includes
– adding a cap and tail consisting of extra
nucleotides at the ends of the RNA transcript,
– removing introns (noncoding regions of the RNA),
and
– RNA splicing, joining exons (the parts of the gene
that are expressed) together to form messenger
RNA (mRNA).
© 2013 Pearson Education, Inc.
The Processing of Eukaryotic RNA
• RNA splicing is believed to play a significant role in
humans
– in allowing our approximately 21,000 genes to
produce many thousands more polypeptides and
– by varying the exons that are included in the final
mRNA.
© 2013 Pearson Education, Inc.
Figure 10.14
DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed Tail
Exons spliced together
mRNA
Coding sequence
Nucleus
Cytoplasm
Translation: The Players
• Translation is the conversion from the nucleic acid
language to the protein language.
© 2013 Pearson Education, Inc.
Messenger RNA (mRNA)
• Translation requires
– mRNA,
– ATP,
– enzymes,
– ribosomes, and
– transfer RNA (tRNA).
© 2013 Pearson Education, Inc.
Transfer RNA (tRNA)
• Transfer RNA (tRNA)
– acts as a molecular interpreter,
– carries amino acids, and
– matches amino acids with codons in mRNA using
anticodons, a special triplet of bases that is
complementary to a codon triplet on mRNA.
© 2013 Pearson Education, Inc.
Figure 10.15
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon
tRNA polynucleotide
(ribbon model)
tRNA
(simplified
representation)
Ribosomes
• Ribosomes are organelles that
– coordinate the functions of mRNA and tRNA and
– are made of two subunits.
• Each subunit is made up of
– proteins and
– a considerable amount of another kind of RNA,
ribosomal RNA (rRNA).
© 2013 Pearson Education, Inc.
Ribosomes
• A fully assembled ribosome holds tRNA and
mRNA for use in translation.
Blast Animation: Roles of RNA
© 2013 Pearson Education, Inc.
Figure 10.16
Next amino acid
to be added to
polypeptide
tRNA
binding sites
P site
Growing
polypeptide
A site
mRNA
binding
site
(a) A simplified diagram
of a ribosome
tRNA
Large
Ribosome
subunit
mRNA
Small
subunit
Codons
(b) The “players” of translation
Figure 10.16a
tRNA binding sites
P site
A site
Large
Ribosome
subunit
mRNA
binding
site
Small
subunit
(a) A simplified diagram of a ribosome
Figure 10.16b
Next amino acid
to be added to
polypeptide
Growing
polypeptide
tRNA
mRNA
Codons
(b) The “players” of translation
Translation: The Process
• Translation is divided into three phases:
1. initiation,
2. elongation, and
3. termination.
© 2013 Pearson Education, Inc.
Initiation
• Initiation brings together
– mRNA,
– the first amino acid with its attached tRNA, and
– two subunits of the ribosome.
• The mRNA molecule has a cap and tail that help
the mRNA bind to the ribosome.
© 2013 Pearson Education, Inc.
Figure 10.17
Cap
Start of genetic
message
End
Tail
Initiation
• Initiation occurs in two steps.
1. An mRNA molecule binds to a small ribosomal
subunit, then a special initiator tRNA binds to the
start codon, where translation is to begin on the
mRNA.
2. A large ribosomal subunit binds to the small one,
creating a functional ribosome.
Animation: Translation
Blast Animation: Translation
© 2013 Pearson Education, Inc.
Figure 10.18
Met
Large
ribosomal
subunit
Initiator
tRNA
P site
mRNA
2
1
Start codon
Small
ribosomal
subunit
A site
Elongation
• Elongation occurs in three steps.
– Step 1: Codon recognition. The anticodon of an
incoming tRNA pairs with the mRNA codon at the
A site of the ribosome.
© 2013 Pearson Education, Inc.
Figure 10.19
Amino acid
Polypeptide
P site
Anticodon
mRNA
A site
Codons
1 Codon recognition
ELONGATION
Stop codon
2 Peptide bond formation
New peptide
bond
mRNA
movement
3 Translocation
Elongation
– Step 2: Peptide bond formation.
– The polypeptide leaves the tRNA in the P site and
attaches to the amino acid on the tRNA in the A
site.
– The ribosome catalyzes the bond formation
between the two amino acids.
© 2013 Pearson Education, Inc.
Figure 10.19a
Amino
acid
Polypeptide
P site
Anticodon
mRNA
A site
Codons
Codon recognition
Peptide bond formation
ELONGATION
Elongation
– Step 3: Translocation.
– The P site tRNA leaves the ribosome.
– The tRNA carrying the polypeptide moves from the
A to the P site.
© 2013 Pearson Education, Inc.
Figure 10.19b
New peptide
bond
mRNA
movement
Translocation
Stop codon
ELONGATION
Termination
• Elongation continues until
– a stop codon reaches the ribosome’s A site,
– the completed polypeptide is freed, and
– the ribosome splits back into its subunits.
© 2013 Pearson Education, Inc.
Review: DNA RNA Protein
• In a cell, genetic information flows from
– DNA to RNA in the nucleus and
– RNA to protein in the cytoplasm.
© 2013 Pearson Education, Inc.
Figure 10.20-1
1 Transcription
RNA polymerase
Nucleus
DNA
mRNA
Intron
Figure 10.20-2
RNA polymerase
1 Transcription
Nucleus
DNA
mRNA
Intron
2 RNA processing
Cap
Tail
Intron
mRNA
Figure 10.20-3
RNA polymerase
1 Transcription
Nucleus
DNA
mRNA
Intron
2 RNA processing
Cap
Tail
Intron
mRNA
Amino acid
tRNA
Anticodon
ATP
Enzyme
3 Amino acid attachment
Figure 10.20-4
RNA polymerase
1 Transcription
Nucleus
DNA
mRNA
Intron
2 RNA processing
Cap
Tail
Intron
mRNA
Amino acid
tRNA
A
Ribosomal
subunits
Anticodon
ATP
Enzyme
3 Amino acid attachment
4 Initiation of
translation
Figure 10.20-5
RNA polymerase
1 Transcription
Nucleus
DNA
mRNA
Intron
Anticodon
2 RNA processing
Codon
Cap
Tail
Intron
mRNA
5 Elongation
Amino acid
tRNA
A
Ribosomal
subunits
Anticodon
ATP
Enzyme
3 Amino acid attachment
4 Initiation of
translation
Figure 10.20-6
RNA polymerase
1 Transcription
Nucleus
DNA
mRNA
Intron
Anticodon
2 RNA processing
Codon
Cap
Tail
Intron
mRNA
5 Elongation
Polypeptide
Amino acid
tRNA
A
Ribosomal
subunits
Stop
codon
Anticodon
ATP
Enzyme
3 Amino acid attachment
4 Initiation of
translation
6 Termination
Review: DNA RNA Protein
• As it is made, a polypeptide
– coils and folds and
– assumes a three-dimensional shape, its tertiary
structure.
• Transcription and translation are how genes
control the structures and activities of cells.
© 2013 Pearson Education, Inc.
Mutations
• A mutation is any change in the nucleotide
sequence of DNA.
• Mutations can change the amino acids in a protein.
• Mutations can involve
– large regions of a chromosome or
– just a single nucleotide pair, as occurs in sickle-cell
disease.
© 2013 Pearson Education, Inc.
Figure 10.21
Normal hemoglobin DNA
Mutant hemoglobin DNA
mRNA
mRNA
Normal hemoglobin
Sickle-cell hemoglobin
Glu
Val
Types of Mutations
• Mutations within a gene can be divided into two
general categories:
1. nucleotide substitutions (the replacement of one
base by another) and
2. nucleotide deletions or insertions (the loss or
addition of a nucleotide).
• Insertions and deletions can
– change the reading frame of the genetic message
and
– lead to disastrous effects.
© 2013 Pearson Education, Inc.
Figure 10.22
Met
Lys
Phe
Gly
mRNA and protein from a normal gene
Met
Lys
Phe
Ser
Ala
Ala
(a) Base substitution
Deleted
Met
Lys
Leu
Ala
(b) Nucleotide deletion
Inserted
Met
Lys
Leu
(c) Nucleotide insertion
Trp
Arg
Figure 10.22a
Met
Lys
Phe
Ala
Gly
mRNA and protein from a normal gene
Met
Lys
Phe
(a) Base substitution
Ser
Ala
Figure 10.22b
Met
Lys
Phe
Ala
Gly
mRNA and protein from a normal gene
Deleted
Met
Lys
Leu
(b) Nucleotide deletion
Ala
Figure 10.22c
Met
Lys
Phe
Ala
Gly
mRNA and protein from a normal gene
Inserted
Met
Lys
Leu
(c) Nucleotide insertion
Trp
Arg
Mutagens
• Mutations may result from
– errors in DNA replication or recombination or
– physical or chemical agents called mutagens.
• Mutations
– are often harmful but
– are useful in nature and the laboratory as a source
of genetic diversity, which makes evolution by
natural selection possible.
© 2013 Pearson Education, Inc.
VIRUSES AND OTHER NONCELLULAR
INFECTIOUS AGENTS
• Viruses share some, but not all, characteristics of
living organisms. Viruses
– possess genetic material in the form of nucleic
acids wrapped in a protein coat,
– are not cellular, and
– cannot reproduce on their own.
© 2013 Pearson Education, Inc.
Figure 10.24a
Protein coat
DNA
Bacteriophages
• Bacteriophages, or phages, are viruses that
attack bacteria.
• Phages consist of a molecule of DNA, enclosed
within an elaborate structure made of proteins.
Animation: Phage T4 Lytic Cycle
Animation: Phage T2 Reproductive Cycle
© 2013 Pearson Education, Inc.
Figure 10.25
Head
Bacteriophage
(200 nm tall)
Tail
Tail
fiber
DNA
of virus
Bacterial cell
Colorized TEM
Bacteriophages
•
Phages have two reproductive cycles.
1. In the lytic cycle,
– many copies of the phage are produced within the
bacterial cell, and
– then the bacterium lyses (breaks open).
© 2013 Pearson Education, Inc.
Bacteriophages
2. In the lysogenic cycle,
– the phage DNA inserts into the bacterial
chromosome and
– the bacterium reproduces normally, copying the
phage at each cell division.
Animation: Phage Lambda Lysogenic and Lytic Cycles
© 2013 Pearson Education, Inc.
Figure 10.26
Phage
1 Phage
Phage DNA
attaches
to cell.
4 Cell lyses,
Bacterial
chromosome (DNA)
releasing
phages.
Phage injects DNA
Many cell
divisions
7 Prophage
may leave
chromosome.
LYSOGENIC
CYCLE
LYTIC CYCLE
Phages assemble
2 Phage DNA
6 Prophage replicated
circularizes.
Prophage
at each normal cell
division.
OR
3 New phage DNA
and proteins are
synthesized.
5 Phage DNA is inserted
into the bacterial
chromosome.
Figure 10.26a
Phage
1 Phage
4
Phage DNA
attaches
to cell.
Cell lyses,
releasing
phages.
Bacterial
chromosome (DNA)
Phage injects DNA
LYTIC CYCLE
Phages assemble
3
2
Phage DNA
circularizes.
New phage DNA and
proteins are synthesized.
Figure 10.26b
Phage
1 Phage
attaches
to cell.
Phage DNA
Bacterial
chromosome (DNA)
Phage injects DNA
Many cell
divisions
7
Prophage
may leave
chromosome.
LYSOGENIC
CYCLE
2
Phage DNA
circularizes.
6
Prophage
5
Prophage replicated
at each normal cell
division.
Phage DNA is inserted into
the bacterial chromosome.
Figure 10.26c
Phage lambda
E. coli
Plant Viruses
• Viruses that infect plants can
– stunt growth and
– diminish plant yields.
• Most known plant viruses have RNA rather than
DNA as their genetic material.
• Many of them, like the tobacco mosaic virus, are
rod-shaped with a spiral arrangement of proteins
surrounding the nucleic acid.
© 2013 Pearson Education, Inc.
Animal Viruses
• Viruses that infect animals cells
– are a common cause of disease and
– may have RNA or DNA genomes.
• Many animal viruses have an outer envelope made
of phospholipid membrane, with projecting spikes
of protein.
© 2013 Pearson Education, Inc.
Figure 10.28
Membranous
envelope
Protein spike
RNA
Protein coat
Animal Viruses
• The reproductive cycle of an enveloped RNA virus
can be broken into seven steps.
Animation: Simplified Viral Reproductive Cycle
© 2013 Pearson Education, Inc.
Figure 10.29
Virus
Viral RNA (genome)
Protein spike
Protein coat
Envelope
Plasma
membrane
of host cell
Viral
RNA
(genome)
mRNA
New
viral
proteins
Template
New viral
genome
Figure 10.29a
Virus
Protein spike
Protein coat
Envelope
Viral RNA
(genome)
Plasma membrane 1
of host cell
Entry
2
Uncoating
3
RNA synthesis
by viral enzyme
Viral RNA
(genome)
Figure 10.29b
4 Protein
synthesis
5
mRNA
New
viral proteins
6
RNA synthesis
(other strand)
Template
Assembly
Exit
7
New viral
genome
Percent reduction in severe
illness and death in
vaccinated group
Figure 10.30a
48
50
40
30
27
20
16
10
0
0
Winter months
(flu season)
Hospitalizations
Summer months
(non-flu season)
Deaths
HIV, the AIDS Virus
• The devastating disease AIDS (acquired
immunodeficiency syndrome) is caused by HIV
(human immunodeficiency virus), an RNA virus
with some special twists.
• HIV is a retrovirus, an RNA virus that reproduces
by means of a DNA molecule.
© 2013 Pearson Education, Inc.
HIV, the AIDS Virus
• Retroviruses use the enzyme reverse
transcriptase to catalyze reverse transcription, the
process of synthesizing DNA on an RNA template.
Blast Animation: HIV Structure
© 2013 Pearson Education, Inc.
Figure 10.31
Envelope
Surface protein
Protein
coat
RNA
(two identical
strands)
Reverse
transcriptase
HIV, the AIDS Virus
• The behavior of HIV nucleic acid in an infected cell
can be broken into six steps.
Animation: HIV Reproductive Cycle
© 2013 Pearson Education, Inc.
Figure 10.32
Cytoplasm
Reverse
transcriptase
Viral RNA
1
DNA
strand
Nucleus
Chromosomal
DNA
2
Provirus
3
Doublestranded
DNA
4
5
RNA
SEM
Viral
RNA
and
proteins
6
HIV (red dots) infecting a white blood cell
Figure 10.32a
Cytoplasm
Reverse
transcriptase
Viral RNA
1
DNA
strand
Nucleus
Chromosomal
DNA
2
Provirus
3
Doublestranded
DNA
4
5
RNA
Viral
RNA
and
proteins
6
HIV, the AIDS Virus
• HIV infects and eventually kills several kinds of
white blood cells that are important in the body’s
immune system.
• While there is no cure for AIDS, its progression can
be slowed by two categories of medicine that
interfere with the reproduction of the virus.
Blast Animation: AIDS Treatment Strategies
© 2013 Pearson Education, Inc.
Figure 10.33
Thymine
(T)
Part of a T nucleotide
AZT
Viroids and Prions
• Two classes of pathogens are smaller than
viruses.
1. Viroids are small, circular RNA molecules that
infect plants.
2. Prions are misfolded proteins that somehow
convert normal proteins to the misfolded prion
version, leading to disease.
© 2013 Pearson Education, Inc.
Viroids and Prions
• Prions are responsible for neurodegenerative
diseases including
– mad cow disease,
– scrapie in sheep and goats,
– chronic wasting disease in deer and elk, and
– Creutzfeldt-Jakob disease in humans.
© 2013 Pearson Education, Inc.
Evolution Connection:
Emerging Viruses
• Emerging viruses are viruses that have suddenly
come to the attention of science. Examples are
– H1N1 and
– avian flu.
© 2013 Pearson Education, Inc.
Evolution Connection:
Emerging Viruses
• Avian flu
– infects birds,
– infected 18 people in Hong Kong in 1997, and
– since has spread to Europe and Africa, infecting
over 400 people and killing more than 240 of them.
• Over 100 million birds have either
– died from the disease or
– been killed to prevent the spread of infection.
© 2013 Pearson Education, Inc.
Evolution Connection:
Emerging Viruses
• If avian flu mutates to a form that can easily spread
between people, the potential for a major human
outbreak is significant.
• New viruses can arise by
– the mutation of existing viruses or
– the spread of existing viruses to a new host
species.
© 2013 Pearson Education, Inc.
Figure 10.UN03
Nitrogenous
base
Phosphate
group
DNA
Sugar
Nucleotide
Polynucleotide
DNA
RNA
Nitrogenous
base
C
G
A
T
C
G
A
U
Sugar
Deoxyribose
Ribose
Number of
strands
2
1
Figure 10.UN03a
Nitrogenous
base
Phosphate
group
DNA
Sugar
Polynucleotide
Nucleotide
Figure 10.UN03b
Nitrogenous
base
Sugar
Number of
strands
DNA
RNA
C
G
A
T
C
G
A
U
DeoxyRibose
ribose
2
1
Figure 10.UN04
Parental
DNA
molecule
New
daughter
strand
Identical
daughter
DNA molecules
Figure 10.UN05
TRANSCRIPTION
TRANSLATION
Gene
mRNA
DNA
Polypeptide
Figure 10.UN06
Growing
polypeptide
Amino acid
Large ribosomal
subunit
tRNA
mRNA
Anticodon
Codons
Small ribosomal
subunit
Figure 10.UN07