Transcript Molecular Biology & Medicine

Molecular Biology
&
Medicine
Figure 16.13
a bacterial
expression
vector produces
lots of the
protein encoded
by a cloned gene
Figure 16.14
strategy for the
production of a
therapeutic protein
Gleevec,
designed
atom
by
atom,
is a
treatment
for
CML
p. 339
Medical Problems Accessible to
Molecular Biology
• “One Gene - One Disease”
– diseases due to single polypeptides
• enzymes of phenylalanine metabolism
–alkaptonuria
–phenylketonuria (PKU)
two defects
in
phenylalanine
catabolism
result
in
different
heritable
diseases
Figure 17.1
Medical Problems Accessible to
Molecular Biology
• “One Gene - One Disease”
– diseases due to single polypeptides
• hemoglobin - a carrier protein
–sickle cell disease
–hemoglobin C disease
–hemoglobin E disease
Figure 17.2
Figure 17.3
Medical Problems Accessible to
Molecular Biology
• “One Gene - One Disease”
– diseases due to single polypeptides
• membrane proteins - receptors &
transporters
–familial hypercholesterolemia
–cystic fibrosis
Medical Problems Accessible to
Molecular Biology
• “One Gene - One Disease”
– diseases due to single polypeptides
• structural proteins
–Duchenne muscular dystrophy
»cells lack dystrophin
–hemophilia
»blood lacks coagulation protein
Medical Problems Accessible to
Molecular Biology
• “One Gene - One Disease”
– diseases due to single polypeptides
• misfolded protein
–Transmissible spongiform
encephalopathies, prion diseases
»Scrapie, “mad cow”, KruetzfeldJacob, kuru
»transmitted by a protein
Figure 17.4
normal
misfolded
Medical Problems Accessible to
Molecular Biology
• molecular analysis requires isolation of the
affected gene(s)
– human genomic libraries can be screened
with sequence-specific probes
• deduced from protein sequence
• from mRNA
• from other species
• identified by a “positional” clue
sequences derived from genes or linked
to genes can be used to isolate the genes
Figure 17.6
RFLPs
serve as natural
genetic markers
that
can be
linked
to genes
Figure 17.7
Heritable Diseases Arise by Mutation
• mutations result from a variety of causes
– point mutations may be spontaneous or
induced
• 5-methylcytosine => thymine mutations
5-mCAA or 5-mCAG =>TAA or TAG
glutamine => stop
5-mCGA=>TGA
arginine => stop
the uracil repair system does not
recognize a 5-MeC=>T mutation
Figure 17.8
Heritable Diseases Arise by Mutation
• mutations result from a variety of causes
– point mutations may be spontaneous or
induced
• silent - no disease
• missense - disease possible
• nonsense - disease probable
Heritable Diseases Arise by Mutation
• mutations result from a variety of causes
– large-scale deletion may remove
• part of a gene
• all of a gene
• several neighboring genes
– inversion or translocation may
• interrupt a gene
• create a new gene
a hybrid
enzyme:
part bcr
(chr 22)
an
active
protein
Kinase
p. 339
and
part abl
(chr 9)
Heritable Diseases Arise by Mutation
• mutations result from a variety of causes
– expanding triplet repeats may cause
progressive heritable diseases
• Fragile-X syndrome
~30 CGG repeats - normal
50-200 repeats - “premutated”
200-1300 repeats - cytosine
methylation, gene inactivation, mental
retardation
18-162 bp
165-600 bp
600-6000 bp
FMR1 promoter region
Figure 17.9
Fragile-X at metaphase
Figure 17.5
Heritable Diseases Arise by Mutation
• mutations result from a variety of causes
– expanding triplet repeats may cause
progressive heritable diseases
• Fragile-X syndrome - CGG repeats
• Myotonic dystrophy - CTG repeats
• Huntington’s disease - CAG repeats
• > 9 others, so far…
– … or not
Molecular Diagnosis: Before the Disease
• genetically characterized diseases can be
detected by various tests
– phenotypic screens
• PKU preliminary screen
the
heel-stick
test
identifies
infants
for
more
testing
Figure
17.10
possible PKU
bacteria
that
require
phe
grow
on PKU
blood,
don’t on
normal
Blood
Figure 17.10
detection of sickle cell allele by RFLP with a
specific restriction enzyme
Figure 17.11
MstII recognizes …CCTNAGG…
The sickle cell allele has …CCTGTGG…
Molecular Diagnosis: Before the Disease
• genetically characterized diseases can be
detected by various tests
– phenotypic screens
– genotypic screens
• identification of known disease-causing
alleles
–allele-specific RFLPs
–allele-specific hybridization
detection
of
sickle cell
allele
by
allelespecific
hybridization
Figure 17.12
Cancer - A Disease of Genetic Changes
• cancer cells differ from normal cells
– division without normal signals to divide
– division in spite normal signals not to divide
Cancer - A Disease of Genetic Changes
• tumor types differ
– benign
• slow-growing, localized, like source tissue
– malignant
• dedifferentiated cells
Figure 17.13
Cancer - A Disease of Genetic Changes
• tumor types differ
– benign
• slow-growing, localized, like source tissue
– malignant
• dedifferentiated cells
– metastatic
• express digestive enzymes
• fail to make cell adhesion proteins
• cause vascularization
Cancer - A Disease of Genetic Changes
• tumor types differ
– different tissues
• carcinomas: epithelial (lung, breast, colon,
liver)
• sarcomas: deep tissues (bone, blood
vessels, muscle)
• leukemias, lymphomas: blood stem cells
Viral agents in cancer
Table 17.1
Cancer - A Disease of Genetic Changes
• varied causes
– viruses (~15%)
• combined with specific mutations
– most cancers (~85%) begin with somatic
mutations
• dividing cells are most susceptible to
mutational consequences
mutations in dividing cells produce
mutant cell populations
Figure 17.14
Cancer - A Disease of Genetic Changes
• two types of genes can lead to cancer
– proto-oncogenes
• normally stimulate cell division
–growth factors
–growth factor receptors
–signal transduction components
–transcription factors
• usually dominant mutations
protooncogenes
normally
stimulate
cell division
Figure 17.15
Cancer - A Disease of Genetic Changes
• two types of genes can lead to cancer
– tumor-suppressor genes
• normally regulate cell division
–cell-adhesion proteins
–DNA repair proteins
–cell cycle control proteins
• generally recessive mutations
Figure 17.17
tumor-suppressor mutations are recessive
Figure 17.16
Cancer - A Disease of Genetic Changes
• metastatic cancers involve the accumulation of
many defects
Figure 17.18
-TS APC
+OG ras
-TS DCC
five mutations
of
tumor suppressor genes
or
proto-oncogenes
lead to
-TS p53
polyp,
benign tumor,
class II & III adenomas,
malignant tumor
+telomerase,
&
-adhesion,
etc.
metastatic cancer
cytotoxic
treatments can be used
to control the spread of
cancer
Figure 17.19
Treatment of Genetic Diseases
• modify the phenotype
– restrict toxic substrates - PKU
– metabolic inhibition - block cholesterol
synthesis
– kill targeted cells - treat cancer with
chemicals that kill fast-growing cells
– administer missing protein - insulin, clotting
factor
example
of
ex vivo
gene
therapy
Figure 17.20
Treatment of Genetic Diseases
• Gene Therapy
– ex vivo
• remove cells from patient
• repair defect in cells
• return cells to patient
but
• returned cells eventually die, so
• altered stem cells may serve as a
permanent source of new cells
Treatment of Genetic Diseases
• Gene Therapy
– in vivo
• repair cells in patient
• requires a delivery method
–dispersal
–gene delivery
Figure 17.22
Figure 17.23
many
human
genes are
alternatively
spliced
Figure 17.24
rapid production of designer
pharmaceuticals
• plant viral expression vectors
– a host plant is infected with an engineered
virus carrying a gene for a specific product
– the same host species can produce protein
from any gene placed in a viral vector
– designer phamaceuticals are produced in
months rather than years