Transcript genes - 基因體學講義

張學偉 生物醫學暨環境生物學系 助理教授
http://genomed.dlearn.kmu.edu.tw
僅供教學使用
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Shortly after you drink a milk
shake, bacteria living in your
large intestine turn on certain
genes
• If a salamander
loses a leg, it can
grow a new one
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• Cancer-causing
genes were first
discovered in a chicken
virus
• Lung cancer causes
more deaths than
any other kind of
cancer
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BIOLOGY AND SOCIETY:
BABY’S FIRST BANK ACCOUNT
• In recent years umbilical cord and placental blood
has been collected at birth.  store in liquid nitrogen
Stem
cells
http://www.sciam.com.tw/read/readshow.asp?FDocNo=4
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Figure 11.1
• Umbilical cord and placental blood is rich in
stem cells
• Stem cells can develop into a wide variety of
different body cells
•  Most cells of the adult lack this ability.
Figure 11.8
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FROM EGG TO ORGANISM:
HOW AND WHY GENES ARE REGULATED
• Four of the many
different types of
human cells
– They all share the
same genome
(a) Three muscle cells (partial)
(b) A nerve cell (partial)
(c) Sperm cells
(d) Blood cells
– What makes them
different?
Genome (基因體;基因組):一個細胞中的所有遺傳物質
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Figure 11.2
• In cellular differentiation
– Certain genes are turned on and off
– Cells become specialized in structure and
function
– It is the regulation of genes that leads to this
specialization.
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Patterns of Gene Expression in Differentiated Cells
• In gene expression
– A gene is turned on and transcribed into RNA
– Information flows from genes to proteins,
genotype to phenotype
• The regulation of gene expression plays a
central role in development from a zygote to a
multicellular organism
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• Patterns of gene
expression in
specialized
human cells
Pancreas
cell
Eye lens cell
(in embryo)
Nerve cell
Glycolysis
enzyme
genes
Crystallin
gene
Insulin
gene
Hemoglobin
gene
Key:
Active
gene
Inactive
gene
Figure 11.3
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DNA Microarrays: Visualizing Gene Expression
• DNA microarray- is a glass slide carrying
thousands of different kinds of single stranded
DNA fragments arranged in an array.
Array (grid)
Glass slide
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參考
DNA Microarrays: Visualizing Gene Expression
• A DNA microarray
allows
visualization of
gene expression
1 mRNA
isolated
Reverse transcriptase and
labeled DNA nucleotides
2 cDNA made
from mRNA
DNA microarray
(each well contains
single stranded
DNA from a
particular gene)
單股
單股
3 cDNA
applied to
wells
4 Unbound cDNA
rinsed away
Fluorescent
spot
Nonfluorescent
spot
cDNA
DNA of gene
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DNA of gene
Figure 11.4a
• The pattern of glowing spots on a microarray
enables researchers to determine which genes
are turned on or off
Figure 11.4b
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The Genetic Potential of Cells- plant & animal
• Differentiated cells
– All contain a complete set of DNA
– May act like other cells if their pattern of gene
expression is altered
• Clones- Genetically identically organisms
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The Genetic Potential of Cells- plant
• Differentiated plant cells
– Have the ability to develop into a
whole new organism
Root of
carrot plant
Plantlet
Cell division
in culture
Single cell
Root cells in
growth medium
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Adult plant
Figure 11.5
The Genetic Potential of Cells- plant
• The somatic cells of a single plant can be
placed in a growing medium to produce clones
• Clones- Genetically identically organisms
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The Genetic Potential of Cells- animal
• Regeneration
– Is the regrowth of lost body parts in animals
– (reverse differentiated state) Re-differentiate
• If a salamander loses a
leg, it can grow a new
one
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Reproductive Cloning of Animals
• Nuclear transplantation
– Involves replacing nuclei of egg cells with nuclei
from differentiated cells
– Has been used to clone a variety of animals
• Scottish researchers cloned the first mammal in
1997
– Dolly, the sheep
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reproductive cloning (individual) & therapeutic cloning (cell)
• The procedure that produced Dolly
is called reproductive cloning
Reproductive cloning
Donor
cell
Nucleus from
donor cell
Implant embryo in
surrogate mother
Clone of donor
is born
Therapeutic cloning
Remove
nucleus
from egg
cell
Add somatic
cell from
adult donor
Grow in culture
to produce an
early embryo
Figure 11.6
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Remove
embryonic stem
cells from embryo
and grow in
culture
Induce stem
cells to form
specialized cells
for therapeutic
use
• Other organisms have since been produced using
this technique, some by the pharmaceutical
industry
(a) Piglets
(b) Banteng
白臀野牛
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Figure 11.7
Therapeutic Cloning and Stem Cells
• Therapeutic cloning
– Produces embryonic stem cells (ES cells)
ES cellsare cells in an early animal embryo that
differentiate during development to give rise to
all the specialized cells in the body.
Development- the process from fertilized egg to embryo
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• Embryonic stem cells- Can give rise to specific types
of differentiated cells
Liver cells
Cultured
embryonic
stem cells
Nerve cells
Heart muscle cells
Different culture
conditions
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Different types of
differentiated cells
Figure 11.8
• Adult stem cells
– Generate replacements for nondividing
differentiated cells
– Are unlike ES cells, because they are partway
along the road to differentiation
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• In 2001, a biotechnology company announced
that it had cloned the first human embryo
Stopped at
6-cell stage
Figure 11.9
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THE REGULATION OF GENE EXPRESSION
• How is gene expression
regulated in a cell?
Chromosome
Unpacking of DNA
DNA
Gene
– The “pipeline” in a
eukaryotic cell
Transcription of
gene
Intron
Exon
RNA transcript
Processing of RNA
Flow of mRNA
through nuclear Cap
Tail
envelope
mRNA in nucleus
mRNA in cytoplasm
Nucleus
Cytoplasm
Translation of
mRNA
Polypeptide
Breakdown
of mRNA
Various changes
to polypeptide
Active protein
Breakdown of
protein
Broken down protein
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Figure 11.10
Gene Regulation in Bacteria
• Bacteria can alter gene expression for
metabolism based on environmental factors
• Control sequences
– Are stretches of DNA that coordinate gene
expression
• An operon 操縱組
– Is a cluster of genes with related functions, including
the control sequences
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• A promoter 啟動子
– Is a control sequence
– Is the site where the transcription enzyme initiates
transcription
• An operator 操作子
– Is a DNA sequence between the promoter and the
enzyme genes [位置關係]
– Acts as an on and off switch for the genes
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• The lac operon in “off” mode
Lactose absent
Operon
Regulatory Promoter Operator
gene
Lactose-utilization genes
DNA
mRNA
Protein
Active
repressor
RNA polymerase
cannot attach to
promoter
(a) Operon turned off (default state when no lactose is present)
Figure 11.11a
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• The lac operon in “on” mode
Lactose present
DNA
mRNA
RNA polymerase bound to
promoter
Protein
Lactose
Inactive
repressor
Enzymes for
lactose utilization
(b) Operon turned on (repressor inactivated by lactose)
Figure 11.11b
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Gene Regulation in the Nucleus of Eukaryotic Cells
• Eukaryotic cells have
more elaborate
mechanisms of gene
expression than
bacteria
DNA unpacking
Transcription
核
RNA processing
RNA transport
Visual Summary 11.4
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The Regulation of DNA Packing
• Cells may use DNA packing for long-term
inactivation of genes
• X chromosome inactivation
– Is seen in female mammals
– Involves one entire X chromosome in each
somatic cell being almost entirely inactive
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Tortoiseshell pattern on a cat
Two cell populations
in adult cat:
Early embryo:
Cell division and
X chromosome
inactivation
Active X
Inactive X
X chromosomes
Orange fur
隨機的
Inactive X
Active X
Black fur
Allele for Allele for
orange fur black fur
other
Orange/orange
black/black
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Orange/orange
black/black
Figure 11.12
Calico cat also has white area, which are determined by
another gene.
Figure 11.12x
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The Initiation of Transcription
The most important stage for regulating gene
expression is transcription.
• Eukaryotic control mechanisms
– Involve regulatory proteins interact with DNA
– Regulate transcription
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Model for turning on of a eukaryotic gene
repressor
Activator
proteins
Transcription
factors
Other
proteins
RNA polymerase
Enhancers
Promoter
Gene
DNA
Bending
of DNA
Transcription
Figure 11.13
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• Each eukaryotic gene
– Has its own promoter and other control
sequences
– May have repressors, which turn genes off
– May have activators, which turn genes on
• Repressors are less common than activators
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• Transcription factors
– Are proteins that turn on eukaryotic genes
• Enhancers [DNA seq]
– Are bound with activator proteins as the first
step in initiating transcription
• Silencers [DNA seq]
– Are repressor proteins that may inhibit the start
of transcription
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• The “default” state for most genes in
multicellular eukaryotes seems to be “off”
with the exception of “ housekeeping” genes for
routine activities.
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RNA Processing
• The eukaryotic cell
– Localizes transcription in the nucleus
– Processes RNA in the nucleus
• RNA processing includes
– The addition of a cap and tail to the RNA
– The removal of any introns
– The splicing together (join) of the remaining
exons
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Producing two different mRNAs from the same gene
Exons
DNA
RNA transcript
Alternative RNA splicing
or
mRNA
Figure 11.14
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Regulation in the Cytoplasm
• After eukaryotic
mRNA is
transported to the
cytoplasm, there are
additional
opportunities for
regulation
mRNA breakdown
細胞質
Translation
Protein activation
Protein breakdown
Visual Summary 11.5
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The Breakdown of mRNA
• Eukaryotic mRNAs
– Can have different
lifetimes
– Are all eventually
broken down and
their parts recycled
Macromolecules
(mRNA, for example)
Synthesis
Breakdown
Monomers
(nucleotides, for example)
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Figure 11.15
The Regulation of Translation
• The process of translation
– May be regulated by many different proteins
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Protein Alterations
• Post-translation control mechanisms
– Occur after translation
– Often involve cutting polypeptides into smaller,
active final products
Cutting
Figure 11.16
Initial polypeptide
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Insulin (active hormone)
Protein Breakdown
• The selective breakdown of proteins is another
control mechanism operating after translation
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Cell Signaling
• In a multicellular organism
– Gene regulation can cross cell boundaries (Cellto-cell signaling: is a key mechanism in the
development of a multicellular organism)
– A cell can produce chemicals that induce
another cell to be regulated a certain way
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• Signal transduction
Signaling cell
1
– Is the main mechanism
of cell-to-cell signaling
Plasma
membrane
Reception
1
Secretion
Signal
molecule
2
2
4
3
protein
3 Receptor
4
Signal-transduction
pathway
Transcription factor
(activated)
Target
cell
Nucleus
5
5
Response
Transcription
New protein
mRNA
6
Translation
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6
Figure 11.17
THE GENETIC BASIS OF CANCER
Genes That Cause Cancer
• As early as 1911 certain viruses were known to
cause cancer
• Cancer-causing viruses often carry specific
genes called oncogenes
• Cancer-causing genes
were first discovered in a
chicken virus
Rous sarcoma virus (RSV, chicken).
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Oncogenes and Tumor-Suppressor Genes
• Proto-oncogenes
– Are normal genes that can become oncogenes
– Are found in many animals
– Code for growth factors that stimulate cell
division
• For a proto-oncogene to become an oncogene,
a mutation must occur in the cell’s DNA
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Proto-oncogene
DNA
(a) Mutation within
the gene
(b) Multiple copies
of the gene
New promoter
Oncogene
Hyperactive
growth-stimulating
protein
(c) Gene moved to
new DNA locus,
under new controls
Normal
growth-stimulating
protein in excess
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Normal
growth-stimulating
protein in excess
Figure 11.18
• Tumor-suppressor genes
– Help prevent uncontrolled cell growth
– May be mutated, and contribute to cancer
Tumor-suppressor gene
Normal
growthinhibiting
protein
Cell division
under control
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Mutated tumor-suppressor gene
Defective,
non-functioning
protein
Cell division
not under
control
Figure 11.19
• Genes That
Cause Cancer
Proto-oncogene
(normal)
Oncogene
Mutation
or virus
Normal
protein
Normal
regulation
of cell cycle
Out-of-control
growth (leading
to cancer)
Normal
growth-inhibiting
protein
Visual Summary 11.6
Tumor-suppressor
gene (normal)
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Mutant
protein
Mutation
or virus
Defective
protein
Mutated
tumor-suppressor
gene
The Effects of Cancer Genes on Cell-Signaling
Pathways
• Normal proto-oncogenes and tumor-suppressor
genes
– Often code for proteins involved in signal
transduction
• The proto-oncogene ras
– Is involved in signal transduction
– Can contribute to cancer if mutated
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The Progression of a Cancer
• Colon cancer begins as an unusually frequent
division of normal-looking cells in the colon lining
Colon wall
1
2
3
Cellular
changes:
Increased
cell division
Growth of benign
tumor
Growth of
malignant tumor
DNA
changes:
Oncogene
activated
Tumor-suppressor
gene inactivated
Second
tumor-suppressor
gene inactivated
(a) Stepwise development of a typical colon cancer
Figure 11.20a
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• Genetic changes or mutations
– Result in altered signal-transduction pathways
Chromosomes
1
mutation
2
mutations
3
mutations
Normal
cell
4
mutations
Malignant
cell
(b) Accumulation of mutations in the development of a cancer cell
Figure 11.20b
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“Inherited” Cancer
• Cancer is always a genetic disease because it
always results from changes in DNA
• In some families, mutations in one or more
genes predisposing the recipient to cancer
can be passed on
– Such a cancer is familial, or inherited
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• Breast cancer
– Has nothing to do with inherited mutations in the
vast majority of cases
– In some families can be caused by inherited
cancer genes
– Can be caused by mutations affecting the
BRCA1 and BRCA2 genes
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The Effects of Lifestyle on Cancer Risk
• Cancer
– Is one of the leading causes of death in the
United States
– Can be caused by carcinogens (cancer causing
agent), e.g. UV radiation, Tobacco, Alcohol
• Exposure to carcinogens
– Is often an individual choice, but can be avoided
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Table 11.1
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EVOLUTION CONNECTION:
HOMEOTIC GENES
• Homeotic genes
effect
– Are master control genes
– Regulate many other genes
– Help direct embryonic development in many
organisms
• Homeoboxes
– Are sequences of nucleotides
common in many organisms
– Can turn groups of genes on and
off during development
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Figure 11.21
Homeotic genes in two different animals
Fly chromosome
Mouse chromosomes
Fruit fly embryo (10 hours)
Mouse embryo (12 days)
Adult fruit fly
Adult mouse
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Figure 11.22