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11.12 Cascades of gene expression and cell-to-cell
signaling direct the development of an
animal
• A cascade of gene expression involves genes for
regulatory proteins that affect other genes
– It determines how an animal develops from a
fertilized egg
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Mutant fruit flies show
the relationship
between gene
expression and
development
– Some mutants have
legs where antennae
should be
Eye
Antenna
Head of a normal fruit fly
Leg
Figure 11.12A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Head of a developmental mutant
ZYGOTE
FERTILIZATION
AND MITOSIS
EMBRYO
Translation of
“head” mRNA
Gradient of
regulatory
protein
4
Gene
expression
5
Gradient of
certain other
proteins
Gene
expression
Body
segments
6
Figure 11.12B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
EMBRYO
Body
segments
6
LARVA
Gene expression
ADULT FLY
7
Head end
Tail end
Figure 11.12B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Fruit flies and mice have similar homeotic
genes (colored boxes)
• The order of
homeotic genes
is the same
• The gene order
corresponds to
analogous body
regions
Fly chromosomes
Mouse chromosomes
Fruit fly embryo (10 hours)
Mouse embryo (12 days)
Adult fruit fly
Adult mouse
Figure 11.14
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
11.14 Key developmental genes are very ancient
• Homeotic genes
– contain nucleotide sequences called
homeoboxes
– are similar in many kinds of organisms
– arose early in the history of life
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
11.13 Signal-transduction pathways convert
messages received at the cell surface into
responses within the cell
• Cell-to-cell signaling is important in
– development
– coordination of cellular activities
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• A signal-transduction
pathway that turns on
a gene
(1) The signaling cell
secretes the signal
molecule
SIGNALING CELL
1
2
TARGET CELL
(2) The signal molecule
binds to a receptor
protein in the target
cell’s plasma
membrane
Figure 11.13
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Signal
molecule
Receptor
protein
Plasma
membrane
SIGNALING CELL
Signal
molecule
1
(3) Binding activates the
first relay protein,
which then activates
the next relay protein,
etc.
(4) The last relay protein
activates a
transcription factor
Figure 11.13
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Receptor
protein
2
Plasma
membrane
3
TARGET CELL
Relay
proteins
Transcription factor
(activated)
4
SIGNALING CELL
Signal
molecule
1
Receptor
protein
2
(5) The transcription
factor triggers
transcription of a
specific gene
Plasma
membrane
3
TARGET CELL
Relay
proteins
Transcription factor
(activated)
(6) Translation of the
mRNA produces a
protein
4
NUCLEUS
DNA
5
Transcription
mRNA
New
protein
6
Figure 11.13
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Translation
THE GENETIC BASIS OF CANCER
11.15 Cancer results from mutations in genes that
control cell division
• A mutation can change a proto-oncogene into
an oncogene
– An oncogene causes cells to divide excessively
Proto-oncogene
Mutation within
the gene
DNA
Multiple copies
of the gene
Oncogene
Hyperactive
growth-stimulating
protein in normal
amount
Gene moved to
new DNA locus,
under new controls
New promoter
Normal growthstimulating
protein
in excess
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Normal growthstimulating
protein
in excess
Figure 11.15A
• Mutations that inactivate tumor-suppressor
genes have similar effects
Tumor-suppressor gene
Mutated tumor-suppressor gene
Normal
growthinhibiting
protein
Defective,
nonfunctioning
protein
Cell division
under control
Cell division not
under control
Figure 11.15B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
11.16 Oncogene proteins and faulty tumorsuppressor proteins can interfere with
normal signal-transduction pathways
• Mutations of these genes cause malfunction of
the pathway
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
GROWTH
FACTOR
Receptor
TARGET CELL
Hyperactive
relay protein
(product of
ras oncogene)
issues signals
on its own
Normal product
of ras gene
Relay
proteins
Transcription factor
(activated)
DNA
NUCLEUS
Transcription
Protein that
STIMULATES
cell division
Translation
Figure 11.16A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Other cancercausing mutations
inhibit the cell’s
ability to repair
damaged DNA
GROWTHINHIBITING
FACTOR
Relay
proteins
Transcription
factor
(activated)
Receptor
Nonfunctional transcription
factor (product of faulty p53
tumor-suppressor gene)
cannot trigger
transcription
Normal product
of p53 gene
Transcription
Translation
Figure 11.16B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Protein that
INHIBITS
cell division
Protein absent
(cell division
not inhibited)
11.17 Multiple genetic changes underlie the
development of cancer
• Cancers result from a series of genetic changes
in a cell lineage
– As in many cancers, the development of colon
cancer is gradual
Colon wall
1
Figure 11.17A
2
3
CELLULAR
CHANGES:
Increased
cell division
Growth of polyp
Growth of malignant
tumor (carcinoma)
DNA
CHANGES:
Oncogene
activated
Tumor-suppressor
gene inactivated
Second tumor-suppressor
gene inactivated
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Mutations that lead to cancer may accumulate
in a lineage of somatic cells
Chromosomes
1
mutation
2
mutations
Normal
cell
3
mutations
4
mutations
Malignant
cell
Figure 11.17B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
11.18 Talking about Science: Mary-Claire King
discusses mutations that cause breast cancer
• Researchers have
gained insight into the
genetic basis of breast
cancer
– Studies have been done
of families in which a
disease-predisposing
mutation is inherited
Figure 11.18
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
11.19 Connection: Avoiding carcinogens can
reduce the risk of cancer
• Lifestyle choices
can help reduce
cancer risk
Table 11.19
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings