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CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Chapters 16 and 17
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
© 2014 Pearson Education, Inc.
 Cell differentiation is the process by which cells
become specialized in structure and function
 The physical processes that give an organism its
shape constitute morphogenesis
 Differential gene expression results from genes
being regulated differently in each cell type
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Cytoplasmic Determinants and Inductive Signals
 Cytoplasmic determinants are maternal
substances in the egg that influence early
development
 As the zygote divides by mitosis, the resulting cells
contain different cytoplasmic determinants, which
lead to gene expression
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 The other major source of developmental information
is the environment around the cell, especially
signals from nearby embryonic cells
 In the process called induction, signal molecules
from embryonic cells cause transcriptional changes
in nearby target cells
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Figure 16.3
(a) Cytoplasmic determinants in the egg
(b) Induction by nearby cells
Unfertilized egg
Sperm
Early embryo
(32 cells)
Nucleus
Fertilization
Zygote
(fertilized
egg)
Mitotic
cell division
Two-celled
embryo
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Molecules of
two different
cytoplasmic
determinants
NUCLEUS
Signal
transduction
pathway
Signal
receptor
Signaling
molecule
(inducer)
Differentiation of Cell Types
 Determination is understood in terms of molecular
changes, the expression of genes for tissuespecific proteins
 The first evidence of differentiation is the production
of mRNAs for these proteins
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Apoptosis: Programmed Cell Death
 Apoptosis is the best-understood type of
“programmed cell death”
 While most cells are differentiating in a developing
organism, some are genetically programmed to
die
 Apoptosis also occurs in the mature organism in
cells that are infected, damaged, or at the end of
their functional lives
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 To initiate apoptosis, DNA is broken up and
organelles and other cytoplasmic components are
fragmented
 These vesicles are then engulfed by scavenger
cells
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 It is essential to development and maintenance
in all animals
 In vertebrates, it is essential for normal nervous
system development and morphogenesis of
hands and feet
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Figure 16.6
1 mm
Interdigital tissue
Cells undergoing apoptosis
Space between digits
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Pattern Formation: Setting Up the Body Plan
 Pattern formation is the development of a spatial
organization of tissues and organs
 In animals, pattern formation begins with the
establishment of the major axes
 Positional information, the molecular cues control
pattern formation. They tell a cell its location relative
to the body axes and to nearby cells
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 Pattern formation has been extensively studied
in the fruit fly Drosophila melanogaster
 Researchers have discovered developmental
principles common to many other species, including
humans
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Figure 16.7a
Head Thorax Abdomen
0.5 mm
Dorsal
BODY Anterior
AXES
Left
Posterior
Ventral
(a) Adult
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Right
Drosophila
Fruit flies and other arthropods have a modular
structure, composed of an ordered series of
segments
 In Drosophila, cytoplasmic determinants in the
unfertilized egg determine the axes before
fertilization
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 The Drosophila eggs develop in the female’s ovary,
surrounded by ovarian cells called nurse cells and
follicle cells
 After fertilization, embryonic development results in a
segmented larva
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Figure 16.7
Head Thorax Abdomen
0.5 mm
Follicle cell
1 Egg
Nucleus
developing within
ovarian follicle
Egg
Nurse cell
Dorsal
BODY Anterior
AXES
Left
Right
Egg
shell
2 Unfertilized egg
Posterior
Depleted
nurse cells
Ventral
Fertilization
Laying of egg
(a) Adult
3 Fertilized egg
Embryonic
development
4 Segmented
embryo
0.1 mm
Body
segments
5 Larval stage
(b) Development from egg to larva
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Hatching
Genetic Analysis of Early Development:
Scientific Inquiry
 Edward B. Lewis, won a Nobel Prize in 1995 for
decoding pattern formation in Drosophila
 Lewis discovered the homeotic genes, which
control pattern formation in late embryo, larva,
and adult stages
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Axis Establishment
 Maternal effect genes code cytoplasmic
determinants that initially establish the axes of the
body of Drosophila
 These maternal effect genes are also called eggpolarity genes because they control orientation of
the egg and consequently the fly
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Bicoid: A Morphogen Determining Head
Structures
 One maternal effect gene, the bicoid gene, affects
the front half of the body
 An embryo whose mother has no functional bicoid
gene lacks the front half of its body and has
duplicate posterior structures at both ends
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Figure 16.9
Head
Tail
T1 T2 T3
A8
A1 A2 A3 A4 A5 A6
Wild-type larva
Tail
250 m
Tail
A8
A7 A6 A7
Mutant larva (bicoid)
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A7
A8
 It is suggested that the product of the mother’s
bicoid gene is concentrated at the future anterior end
and is required for setting up the anterior end of the
fly
 Gradients of substances called morphogens
establish an embryo’s axes and other features
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 The bicoid mRNA is highly concentrated at the
anterior end of the embryo
 After the egg is fertilized, the mRNA is translated into
Bicoid protein, which diffuses from the anterior end
this results in a gradient of bicoid protein
 Injection of bicoid mRNA into various regions of
an embryo results in the formation of anterior
structures at the site of injection
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Figure 16.10
100 m
Results
Anterior end
Fertilization,
translation of
bicoid mRNA
Bicoid mRNA in mature
unfertilized egg
Bicoid protein in
early embryo
Bicoid mRNA in mature
unfertilized egg
Bicoid protein in
early embryo
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Bicoid and Pattern Formation
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 The bicoid research is important for three reasons
 It identified a specific protein required for some
early steps in pattern formation
 It increased understanding of the mother’s role in
embryo development
 A key principle, that a gradient of molecules can
determine polarity and position in the embryo
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Cloning Plants and Animals
 Single differentiated cells from the root of carrot
plants in culture medium were able to grow into
complete adult plants
 This work showed that differentiation is not
necessarily irreversible
 Cells that can give rise to all the specialized cell
types in the organism are called totipotent
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 Experiments with frog embryos showed the older the
donor nucleus, the lower the percentage of normally
developing tadpoles
 John Gurdon concluded from this work that nuclear
potential is restricted as development and
differentiation proceeds
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Figure 16.11
Experiment
Frog egg cell
Frog embryo
Frog tadpole
UV
Results
Less differentiated cell
Fully differentiated
(intestinal) cell
Donor
nucleus
transplanted
Donor
nucleus
transplanted
Enucleated
egg cell
Egg with donor nucleus
activated to begin
development
Most develop
into tadpoles.
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Most stop developing
before tadpole stage.
Reproductive Cloning of Mammals
 In 1997, Scottish researchers announced the birth of
Dolly, a lamb cloned from an adult sheep by nuclear
transplantation from a differentiated cell
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Figure 16.12
Technique
Mammary
cell donor
1
Egg cell
donor
2
Nucleus
removed
Cultured
mammary
cells
3 Cells fused
Cell cycle
arrested,
causing cells to
dedifferentiate
4 Grown in culture
Egg cell
from ovary
Nucleus from
mammary cell
Early embryo
5
Implanted in uterus
of a third sheep
Surrogate
mother
6
Embryonic
development
Results
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Lamb (“Dolly”)
genetically identical to
mammary cell donor
 Since 1997, cloning has been demonstrated in many
mammals, including mice, cats, cows, horses, mules,
pigs, and dogs
 Cloned animals do not always look or behave
exactly the same as their “parent”
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Figure 16.13
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Faulty Gene Regulation in Cloned Animals
 In most nuclear transplantation studies, only a small
percentage of cloned embryos have developed
normally to birth
 Many cloned animals exhibit defects due to Faulty
Gene Regulation
 Epigenetic changes must be reversed in the
nucleus from a donor animal in order for genes to
be expressed or repressed appropriately for early
stages of development
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Stem Cells of Animals
 A stem cell is a relatively unspecialized cell that can
reproduce itself indefinitely and differentiate into
specialized cells of one or more types
 Stem cells isolated from early embryos at the
blastocyst stage are called embryonic stem (ES)
cells; these are able to differentiate into all cell
types
 The adult body also has stem cells, which replace
non-reproducing specialized cells (Adult Stem Cells)
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Figure 16.14
Stem cell
Cell
division
Stem cell
and
Fat cells
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Precursor cell
or
Bone cells
or
White
blood cells
Figure 16.15
Embryonic
stem cells
Cells that can generate
all embryonic cell types
Adult
stem cells
Cells that generate a limited
number of cell types
Cultured
stem cells
Different
culture
conditions
Liver cells Nerve cells Blood cells
Different
types of
differentiated
cells
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 ES cells are pluripotent, capable of differentiating
into many cell types
 Researchers are able to reprogram fully differentiated
cells to act like ES cells using retroviruses
 Cells transformed this way are called iPS, or
induced pluripotent stem cells
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 Cells of patients suffering from certain diseases
can be reprogrammed into iPS cells for use in
testing potential treatments
 In the field of regenerative medicine, a patient’s
own cells might be reprogrammed into iPS cells to
potentially replace the nonfunctional (diseased) cells
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Abnormal regulation of genes that affect the cell
cycle can lead to cancer
 The gene regulation systems that go wrong during
cancer are the same systems involved in embryonic
development
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Types of Genes Associated with Cancer
 Cancer research led to the discovery of cancercausing genes called oncogenes in certain types
of viruses
 The normal version of such genes, called protooncogenes, code for proteins that stimulate normal
cell growth and division
 An oncogene arises from a genetic change leading
to either an increase in the amount or the activity of
the protein product of the gene
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 Proto-oncogenes can be converted to oncogenes
by:
1. Movement of the oncogene to a position near an
active promoter, which may increase transcription
2. Amplification, increasing the number of copies of a
proto-oncogene
3. Point mutations in the proto-oncogene or its control
elements, causing an increase in gene expression
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Figure 16.16
Proto-oncogene
Translocation
or transposition:
gene moved to
new locus, under
new controls
Proto-oncogene
Proto-oncogene
Gene amplification:
multiple copies of
the gene
Point mutation:
New Oncogene
promoter
Normal growthstimulating protein
in excess
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Normal growthstimulating protein
in excess
within a control
element
within
the gene
Oncogene
Oncogene
Normal growthstimulating
protein in
excess
Hyperactive or
degradationresistant
protein
 Tumor-suppressor genes encode proteins that
help prevent uncontrolled cell growth
 Mutations that decrease protein products of tumorsuppressor genes may contribute to cancer onset
 Tumor-suppressor proteins
 Repair damaged DNA
 Control cell adhesion
 Inhibit the cell cycle
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Interference with Cell-Signaling Pathways
 Mutations in the ras proto-oncogene and p53
tumor-suppressor gene are common in human
cancers
 Mutations in the ras gene can lead to production of
a hyperactive Ras protein and increased cell
division
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 Suppression of the cell cycle can be important in
the case of damage to a cell’s DNA;
 p53 prevents a cell from passing on mutations due
to DNA damage
 Mutations in the p53 gene prevent suppression of
the cell cycle “ Guardian of the Genome”
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Figure 16.17
1 Growth factor
3 G protein
Ras
GTP
2 Receptor
5
NUCLEUS
Transcription
factor (activator)
6 Protein that
NUCLEUS
Transcription
factor (activator)
Overexpression
of protein
stimulates
the cell cycle
4 Protein
kinases
MUTATION
Ras
GTP
Ras protein active with
or without growth factor.
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Figure 16.18
2 Protein kinases
NUCLEUS
Protein that
inhibits the
cell cycle
UV
light
1 DNA damage
in genome
UV
light
3 Active form
of p53
MUTATION
DNA damage
in genome
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Defective
or missing
transcription
factor
Inhibitory
protein
absent
Inherited Predisposition and Other Factors
Contributing to Cancer
 Individuals can inherit oncogenes or mutant
alleles of tumor-suppressor genes
 Inherited mutations in the tumor-suppressor gene
adenomatous polyposis coli (APC) are common in
individuals with colorectal cancer
 Mutations in the BRCA1 or BRCA2 gene are found
in at least half of inherited breast cancers, and tests
using DNA sequencing can detect these mutations
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 DNA breakage can contribute to cancer, thus the
risk of cancer can be lowered by minimizing
exposure to agents that damage DNA, such as UV
Radiation, Toxins and chemicals found in cigarette
smoke
 Viruses play a role in about 15% of human
cancers by donating an oncogene to a cell,
disrupting a tumor-suppressor gene, or converting
a proto-oncogene into an oncogene ( HPV )
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Virus: A Borrowed Life
 A virus is an infectious particle consisting of little
more than genes packaged into a protein coat
 They live off of cells that already exist
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Figure 17.1
0.25 m
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 Viruses are not cells but are a nucleic acid
enclosed in a protein coat
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Viral Genomes
 Viral genomes may consist of either
 Double or Single-stranded DNA
 Double- or single-stranded RNA
 Depending on its type of nucleic acid, a virus is
called a DNA virus or an RNA virus
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Capsids and Envelopes
 A capsid is the protein shell that encloses the
viral genome
 A capsid can have various structures
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 Bacteriophages, also called phages, are viruses
that infect bacteria
 Phages have an elongated
capsid head that encloses
DNA
 A protein tail piece attaches
the host and injects the
phage DNA inside
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their
the phage to
Viruses replicate only in host cells
 Viruses are obligate intracellular parasites, which
means they can replicate only within a host cell
 Each virus has a host range, a limited number of
host cells that it can infect
 West Nile
 Measles
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Replicative Cycles of Phages
 Phages are the best understood of all viruses
 Phages have two reproductive mechanisms: the
lytic cycle and the lysogenic cycle
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The Lytic Cycle
 The lytic cycle is a phage replicative cycle that
culminates in the death of the host cell
 The lytic cycle produces new phages and lyses the
host’s cell wall, releasing the more viruses
 A phage that reproduces only by the lytic cycle is
called a virulent phage
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Figure 17.4-5
1 Attachment
2 Entry of phage
5 Release
DNA and
degradation
of host DNA
Phage assembly
4 Assembly
Head
Tail
Tail
fibers
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3 Synthesis of
viral genomes
and proteins
The Lysogenic Cycle
 The lysogenic cycle replicates the phage genome
without destroying the host
 The viral DNA molecule is incorporated into the
host cell’s chromosome
 This integrated viral DNA is known as a prophage
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Figure 17.5b
Daughter cell
with prophage
Many cell
divisions
create many
infected
bacteria.
Prophage exits
chromosome.
Lysogenic cycle
Prophage
Prophage is copied
with bacterial
chromosome.
Phage DNA integrates into
bacterial chromosome.
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Animation of Cycles
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Animal Virus and Viral Envelopes
 An animal virus with an envelope uses it to enter the
host cell that help them infect the
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RNA as Viral Genetic Material
 Retroviruses use reverse transcriptase to copy
their RNA genome into DNA
 HIV (human immunodeficiency virus) is the
retrovirus that causes AIDS (acquired
immunodeficiency syndrome)
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 Viral DNA that is integrated into the host genome is
called a provirus
 Unlike a prophage, a provirus is a permanent
resident of the host cell
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Figure 17.7b
HIV
Membrane of
white blood cell
0.25 m
HIV entering a cell
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New HIV leaving a cell
Emerging Viruses
 Viruses that suddenly become apparent are called
emerging viruses
 HIV is a classic example
 The West Nile virus appeared in North America
first in 1999 and has now spread to 48 states
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 Three processes contribute to the emergence of viral
diseases
 The mutation of existing viruses, which is
especially high in RNA viruses
 Dissemination of a viral disease from a small, isolated
human population, allowing the disease to go
unnoticed before it begins to spread
 Spread of existing viruses from animal populations;
about three-quarters of new human diseases
originate this way
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Figure 17.8
1 m
(a) 2009 pandemic H1N1
influenza A virus
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(b) 2009 pandemic screening
 A vaccine is a harmless derivative of a pathogen
that stimulates the immune system to mount
defenses against the harmful pathogen
 Vaccines can prevent certain viral illnesses
 Viral infections cannot be treated by antibiotics
 Antiviral drugs can help to treat, though not cure,
viral infections
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