results experiment conclusion growth: wild-type cells growing and dividing no growth: mutant cells...
TRANSCRIPT
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RESULTS
EXPERIMENT
CONCLUSION
Growth:Wild-typecells growing and dividing
No growth:Mutant cellscannot grow and divide
Minimal medium
Classes of Neurospora crassa
Wild type Class I mutants Class II mutants Class III mutants
Minimalmedium(MM)(control)
MM +ornithine
MM +citrulline
Co
nd
itio
n
MM +arginine(control)
Class I mutants(mutation in
gene A)Wild type
Class II mutants(mutation in
gene B)
Class III mutants(mutation in
gene C)
Gene A
Gene B
Gene C
Precursor Precursor Precursor PrecursorEnzyme A Enzyme AEnzyme A Enzyme A
Enzyme B
Ornithine Ornithine Ornithine OrnithineEnzyme B Enzyme B Enzyme B
Citrulline Citrulline Citrulline CitrullineEnzyme C Enzyme C Enzyme C Enzyme C
Arginine Arginine Arginine Arginine
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TRANSCRIPTION
TRANSLATION
DNA
mRNARibosome
Polypeptide
(a) Bacterial cell
Nuclearenvelope
TRANSCRIPTION
RNA PROCESSINGPre-mRNA
DNA
mRNA
TRANSLATION Ribosome
Polypeptide
(b) Eukaryotic cell
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DNAmolecule
Gene 1
Gene 2
Gene 3
DNAtemplatestrand
TRANSCRIPTION
TRANSLATION
mRNA
Protein
Codon
Amino acid
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Second mRNA base
Fir
st
mR
NA
ba
se
(5 e
nd
of
co
do
n)
Th
ird
mR
NA
ba
se
(3 e
nd
of
co
do
n)
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(a) Tobacco plant expressing a firefly gene
(b) Pig expressing a jellyfish gene
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Promoter Transcription unit
Start pointDNA
RNA polymerase
5533
Initiation1
2
3
5533
UnwoundDNA
RNAtranscript
Template strandof DNA
Elongation
RewoundDNA
5
55
5
5
33
3
3
RNAtranscript
Termination
5533
35Completed RNA transcript
Newly madeRNA
Templatestrand of DNA
Direction oftranscription(“downstream”)
3 end
RNApolymerase
RNA nucleotides
Nontemplatestrand of DNA
Elongation
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A eukaryotic promoterincludes a TATA box
3
1
2
3
Promoter
TATA box Start point
Template
TemplateDNA strand
535
Transcriptionfactors
Several transcription factors mustbind to the DNA before RNApolymerase II can do so.
5533
Additional transcription factors bind tothe DNA along with RNA polymerase II,forming the transcription initiation complex.
RNA polymerase IITranscription factors
55 53
3
RNA transcript
Transcription initiation complex
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Protein-coding segment Polyadenylation signal3
3 UTR5 UTR
5
5 Cap Start codon Stop codon Poly-A tail
G P PP AAUAAA AAA AAA…
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Pre-mRNA
mRNA
Codingsegment
Introns cut out andexons spliced together
5 Cap
Exon Intron5
1 30 31 104
Exon Intron
105
Exon
146
3Poly-A tail
Poly-A tail5 Cap
5 UTR 3 UTR1 146
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RNA transcript (pre-mRNA)
Exon 1 Exon 2Intron
ProteinsnRNA
snRNPs
Otherproteins
5
5
Spliceosome
Spliceosomecomponents
Cut-outintronmRNA
Exon 1 Exon 25
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GeneDNA
Exon 1 Exon 2 Exon 3Intron Intron
Transcription
RNA processing
Translation
Domain 2
Domain 3
Domain 1
Polypeptide
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Polypeptide
Ribosome
Aminoacids
tRNA withamino acidattached
tRNA
Anticodon
TrpPhe Gly
Codons 35
mRNA
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Amino acidattachment site
3
5
Hydrogenbonds
Anticodon
(a) Two-dimensional structure
Amino acidattachment site
5
3
Hydrogenbonds
3 5AnticodonAnticodon
(c) Symbol used in this book(b) Three-dimensional structure
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Amino acid Aminoacyl-tRNAsynthetase (enzyme)
ATP
AdenosineP P P
AdenosineP
PP i
PPi
i
tRNA
tRNA
Aminoacyl-tRNAsynthetase
Computer model
AMPAdenosineP
Aminoacyl-tRNA(“charged tRNA”)
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Growingpolypeptide Exit tunnel
Largesubunit
Smallsubunit
tRNAmolecules
E PA
mRNA5 3
(a) Computer model of functioning ribosome
P site (Peptidyl-tRNAbinding site)
E site(Exit site)
A site (Aminoacyl-tRNA binding site)
E P A Largesubunit
mRNAbinding site
Smallsubunit
(b) Schematic model showing binding sites
Amino end Growing polypeptide
Next amino acidto be added topolypeptide chain
mRNAtRNAE
3
5 Codons
(c) Schematic model with mRNA and tRNA
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3355U
UA
ACGMet
GTP GDPInitiator
tRNA
mRNA
5 3Start codon
mRNA binding site
Smallribosomalsubunit
5
P site
Translation initiation complex
3
E A
Met
Largeribosomalsubunit
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Amino endof polypeptide
mRNA
5
3E
Psite
Asite
GTP
GDP
E
P A
E
P A
GDPGTP
Ribosome ready fornext aminoacyl tRNA
E
P A
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Releasefactor
3
5Stop codon(UAG, UAA, or UGA)
5
32
Freepolypeptide
2 GDP
GTP
5
3
18
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Growingpolypeptides
Completedpolypeptide
Incomingribosomalsubunits
Start ofmRNA(5 end)
Polyribosome
End ofmRNA(3 end)
(a)
Ribosomes
mRNA
(b) 0.1 µm
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Ribosome
mRNA
Signalpeptide
Signal-recognitionparticle (SRP)
CYTOSOL Translocationcomplex
SRPreceptorprotein
ER LUMEN
Signalpeptideremoved
ERmembrane
Protein
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Wild-type hemoglobin DNA
mRNA
Mutant hemoglobin DNA
mRNA
33
3
3
3
3
55
5
55
5
C CT T TTG GA A AA
A A AGG U
Normal hemoglobin Sickle-cell hemoglobin
Glu Val
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Wild-type
3DNA template strand
5
5
53
3
Stop
Carboxyl endAmino end
Protein
mRNA
33
3
55
5
A instead of G
U instead of C
Silent (no effect on amino acid sequence)
Stop
T instead of C
33
3
55
5
A instead of G
Stop
Missense
A instead of T
U instead of A
33
3
5
5
5
Stop
Nonsense No frameshift, but one amino acid missing (3 base-pair deletion)
Frameshift causing extensive missense (1 base-pair deletion)
Frameshift causing immediate nonsense (1 base-pair insertion)
5
5
533
3
Stop
missing
missing
3
3
3
5
55
missing
missing
Stop
5
5533
3
Extra U
Extra A
(a) Base-pair substitution (b) Base-pair insertion or deletion
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RNA polymerase
DNA
Polyribosome
mRNA
0.25 µmDirection oftranscription
DNA
RNApolymerase
Polyribosome
Polypeptide(amino end)
Ribosome
mRNA (5 end)
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TRANSCRIPTION
RNA PROCESSING
DNA
RNAtranscript
3
5RNApolymerase
Poly-A
Poly-A
RNA transcript(pre-mRNA)
Intron
Exon
NUCLEUS
Aminoacyl-tRNAsynthetase
AMINO ACID ACTIVATIONAminoacid
tRNACYTOPLASM
Poly-A
Growingpolypeptide
3
Activatedamino acid
mRNA
TRANSLATION
Cap
Ribosomalsubunits
Cap
5
E
P
A
AAnticodon
Ribosome
Codon
E
24