Transcript video slide - Independent School District 196

Chapter 17
From Gene to Protein
PowerPoint TextEdit Art Slides for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 17.1 A ribosome, part of the protein
synthesis machinery
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Figure 17.3 Overview: the roles of transcription and
translation in the flow of genetic information (layer 1)
TRANSCRIPTION
DNA
(a) Prokaryotic cell. In a cell lacking a nucleus, mRNA
produced by transcription is immediately translated
without additional processing.
(b) Eukaryotic cell. The nucleus provides a separate
compartment for transcription. The original RNA
transcript, called pre-mRNA, is processed in various
ways before leaving the nucleus as mRNA.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 17.3 Overview: the roles of transcription and
translation in the flow of genetic information (layer 2)
TRANSCRIPTION
DNA
mRNA
TRANSLATION
Ribosome
Polypeptide
(a) Prokaryotic cell. In a cell lacking a nucleus, mRNA
produced by transcription is immediately translated
without additional processing.
(b) Eukaryotic cell. The nucleus provides a separate
compartment for transcription. The original RNA
transcript, called pre-mRNA, is processed in various
ways before leaving the nucleus as mRNA.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 17.3 Overview: the roles of transcription and
translation in the flow of genetic information (layer 3)
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
(a) Prokaryotic cell. In a cell lacking a nucleus, mRNA
produced by transcription is immediately translated
without additional processing.
Nuclear
envelope
TRANSCRIPTION
DNA
(b) Eukaryotic cell. The nucleus provides a separate
compartment for transcription. The original RNA
transcript, called pre-mRNA, is processed in various
ways before leaving the nucleus as mRNA.
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Figure 17.3 Overview: the roles of transcription and
translation in the flow of genetic information (layer 4)
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
(a) Prokaryotic cell. In a cell lacking a nucleus, mRNA
produced by transcription is immediately translated
without additional processing.
Nuclear
envelope
TRANSCRIPTION
DNA
RNA PROCESSING
Pre-mRNA
mRNA
(b) Eukaryotic cell. The nucleus provides a separate
compartment for transcription. The original RNA
transcript, called pre-mRNA, is processed in various
ways before leaving the nucleus as mRNA.
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Figure 17.3 Overview: the roles of transcription and
translation in the flow of genetic information (layer 5)
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
(a) Prokaryotic cell. In a cell lacking a nucleus, mRNA
produced by transcription is immediately translated
without additional processing.
Nuclear
envelope
TRANSCRIPTION
DNA
RNA PROCESSING
Pre-mRNA
mRNA
Ribosome
TRANSLATION
Polypeptide
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(b) Eukaryotic cell. The nucleus provides a separate
compartment for transcription. The original RNA
transcript, called pre-mRNA, is processed in various
ways before leaving the nucleus as mRNA.
Figure 17.4 The triplet code
DNA
molecule
Gene 2
Gene 1
Gene 3
DNA strand
(template)
5
3
A
C
C
A
A
A
C
C
G
A
G
T
U G
G
U
U
U
G G
C
U
C
A
TRANSCRIPTION
mRNA
5
Codon
TRANSLATION
Protein
Trp
Amino acid
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Phe
Gly
Ser
3
Figure 17.5 The dictionary of the genetic code
Second mRNA base
C
UUU
UUC
U
UUA
First mRNA base (5 end)
A
UAU
UCU
Phe
UCC
UCA
UAC
Ser
U
UGU
Tyr
UGC
Cys
C
UCG
CUU
CCU
CAU
CUC
CCC
CAC
CUA
Leu
Leu CCA Pro
CAA
CUG
CCG
CAG
AUU
ACU
AAU
ACC
AAC
AUC
lle
AUA
ACA
Thr
AAG
GUU
GCU
GAU
GUC
GCC
GAC
GUA
GUG
Val
GCA
Ala
GCG
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His
Gln
Asn
AAA
AUGMet or ACG
start
G
G
UAA Stop UGA Stop A
UAG Stop UGG Trp G
UUG
C
A
Lys
CGC
CGA
Arg
Asp
CGG
G
AGU
U
AGC
Ser C
AGA
A
AGG Arg G
GGC
GGA
Glu
C
A
U
GGU
GAA
GAG
U
CGU
GGG
Gly
C
A
G
Third mRNA base (3 end)
U
Figure 17.6 A tobacco plant expressing a firefly gene
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Figure 17.7 The stages of transcription: initiation,
elongation, and termination (layer 1)
Promoter
Transcription unit
5
3
3
5
Start point
RNA polymerase
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DNA
Figure 17.7 The stages of transcription: initiation,
elongation, and termination (layer 2)
Promoter
Transcription unit
5
3
3
5
Start point
DNA
1 Initiation. After RNA polymerase binds to
RNA polymerase
the promoter, the DNA strands unwind, and
the polymerase initiates RNA synthesis at the
start point on the template strand.
5
3
3
5
Template strand of DNA
Unwound
RNA
DNA
transcript
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Figure 17.7 The stages of transcription: initiation,
elongation, and termination (layer 3)
Promoter
Transcription unit
5
3
3
5
Start point
DNA
1 Initiation. After RNA polymerase binds to
RNA polymerase
the promoter, the DNA strands unwind, and
the polymerase initiates RNA synthesis at the
start point on the template strand.
5
3
3
5
Template strand of DNA
Unwound
RNA
DNA
transcript
2 Elongation. The polymerase moves downstream, unwinding the
Rewound
DNA and elongating the RNA transcript 5  3 . In the wake of
transcription, the DNA strands re-form a double helix.
RNA
5
3
3
5
RNA
transcript
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3
5
Figure 17.7 The stages of transcription: initiation,
elongation, and termination (layer 4)
Promoter
Transcription unit
5
3
3
5
Start point
DNA
1 Initiation. After RNA polymerase binds to
RNA polymerase
the promoter, the DNA strands unwind, and
the polymerase initiates RNA synthesis at the
start point on the template strand.
5
3
3
5
Template strand of DNA
Unwound
RNA
DNA
transcript
2 Elongation. The polymerase moves downstream, unwinding the
Rewound
DNA and elongating the RNA transcript 5  3 . In the wake of
transcription, the DNA strands re-form a double helix.
RNA
5
3
3
5
3
5
RNA
transcript
3 Termination. Eventually, the RNA
transcript is released, and the
polymerase detaches from the DNA.
5
3
3
5
3
5
Completed RNA transcript
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Non-template
strand of DNA
Elongation
RNA nucleotides
RNA
polymerase
A
T
C
C
A
A
3
3 end
U
5
A
E
G
C
A
T
A
G
G
T
T
Direction of transcription
(“downstream)
5
Newly made
RNA
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Template
strand of DNA
Figure 17.8 The initiation of transcription at a
eukaryotic promoter
TRANSCRIPTION
1 Eukaryotic promoters
DNA
RNA PROCESSING
Pre-mRNA
mRNA
TRANSLATION
Ribosome
Polypeptide
Promoter
5
3
3
5
T A T A A AA
ATAT T T T
TATA box
Start point
Template
DNA strand
2 Several transcription
factors
Transcription
factors
5
3
3
5
3 Additional transcription
factors
RNA polymerase II
Transcription factors
5
3
3
5
5
RNA transcript
Transcription initiation complex
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Figure 17.9 RNA processing: addition of the 5 cap
and poly-A tail
A modified guanine nucleotide
added to the 5 end
TRANSCRIPTION
RNA PROCESSING
50 to 250 adenine nucleotides
added to the 3 end
DNA
Pre-mRNA
5
mRNA
Protein-coding segment
Polyadenylation signal
3
G P P P
AAUAAA
AAA…AAA
Ribosome
TRANSLATION
5 Cap
5 UTR
Start codon Stop codon
Polypeptide
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3 UTR
Poly-A tail
Figure 17.10 RNA processing: RNA splicing
TRANSCRIPTION
RNA PROCESSING
DNA
Pre-mRNA
5 Exon Intron
Pre-mRNA 5 Cap
30
31
1
Coding
segment
mRNA
Ribosome
Intron
Exon
Exon
3
Poly-A tail
104
105
146
Introns cut out and
exons spliced together
TRANSLATION
Polypeptide
mRNA
5 Cap
1
3 UTR
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Poly-A tail
146
3 UTR
Figure 17.11 The roles of snRNPs and spliceosomes
in pre-mRNA splicing
RNA transcript (pre-mRNA)
5
Intron
Exon 1
Exon 2
Protein
1
Other proteins
snRNA
snRNPs
Spliceosome
2
5
Spliceosome
components
3
mRNA
5
Exon 1
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Exon 2
Cut-out
intron
Figure 17.12 Correspondence between exons and
protein domains
Gene
DNA
Exon 1 Intron Exon 2
Intron Exon 3
Transcription
RNA processing
Translation
Domain 3
Domain 2
Domain 1
Polypeptide
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Figure 17.13 Translation: the basic concept
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
Amino
acids
Polypeptide
Ribosome
tRNA with
amino acid
attached
Gly
tRNA
Anticodon
A A A
U G G U U U G G C
Codons
5
mRNA
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3
Figure 17.14 The structure of transfer RNA (tRNA)
3
A
Amino acid
C
attachment site
C
A 5
C G
G C
C G
U G
U A
A U
A U
U C
*
G
U
AG *
CACA
A CUC
*
G
*
U
G
U
G
G
*
C
CGAG
C
* *
AGG
U
*
* GA
G C
Hydrogen
G C
bonds
U A
* G
* A
A
C
*
U
A
A G
Anticodon
(a) Two-dimensional structure. The four base-paired regions and three loops are characteristic of all tRNAs,
as is the base sequence of the amino acid attachment site at the 3 end. The anticodon triplet is unique to
each tRNA type. (The asterisks mark bases that have been chemically modified, a characteristic of tRNA.)
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5
3
Amino acid
attachment site
Hydrogen
bonds
A
3
Anticodon
(b) Three-dimensional structure
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A G
Anticodon
5
(c) Symbol used
in this book
Figure 17.15 An aminoacyl-tRNA synthetase joins
a specific amino acid to a tRNA
Amino acid
Aminoacyl-tRNA
synthetase (enzyme)
1 Active site binds the
amino acid and ATP.
P P P Adenosine
ATP
2 ATP loses two P groups
and joins amino acid as AMP.
P Adenosine
Pyrophosphate
Pi
Phosphates
P Pi
Pi
tRNA
3 Appropriate
tRNA covalently
Bonds to amino
Acid, displacing
AMP.
P Adenosine
AMP
4 Activated amino acid
is released by the enzyme.
Aminoacyl tRNA
(an “activated
amino acid”)
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Figure 17.16 The anatomy of a functioning ribosome
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
Exit tunnel
Growing
polypeptide
tRNA
molecules
Large
subunit
E
P A
Small
subunit
5
mRNA
3
(a) Computer model of functioning ribosome. This is a model of a bacterial ribosome, showing its overall
shape. The eukaryotic ribosome is roughly similar. A ribosomal subunit is an aggregate of ribosomal
RNA molecules and proteins.
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P site (Peptidyl-tRNA
binding site)
A site (AminoacyltRNA binding site)
E site
(Exit site)
Large
subunit
E
mRNA
binding site
P
A
Small
subunit
(b) Schematic model showing binding sites. A ribosome has an mRNA binding site and three tRNA
binding sites, known as the A, P, and E sites. This schematic ribosome will appear in later diagrams.
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Amino end
Growing polypeptide
Next amino acid
to be added to
polypeptide chain
tRNA
3
mRNA
5
Codons
(c) Schematic model with mRNA and tRNA. A tRNA fits into a binding site when its anticodon base-pairs with
an mRNA codon. The P site holds the tRNA attached to the growing polypeptide. The A site holds the tRNA
carrying the next amino acid to be added to the polypeptide chain. Discharged tRNA leaves via the E site.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 17.17 The initiation of translation
Large
ribosomal
subunit
P site
3 U A C 5
5 A U G 3
Initiator tRNA
GTP
GDP
E
A
mRNA
5
Start codon
3
mRNA binding site
Small
ribosomal
subunit
1 A small ribosomal subunit binds to a molecule of
mRNA. In a prokaryotic cell, the mRNA binding site
on this subunit recognizes a specific nucleotide
sequence on the mRNA just upstream of the start
codon. An initiator tRNA, with the anticodon UAC,
base-pairs with the start codon, AUG. This tRNA
carries the amino acid methionine (Met).
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5
3
Translation initiation complex
2 The arrival of a large ribosomal subunit completes
the initiation complex. Proteins called initiation
factors (not shown) are required to bring all the
translation components together. GTP provides
the energy for the assembly. The initiator tRNA is
in the P site; the A site is available to the tRNA
bearing the next amino acid.
Figure 17.18 The elongation cycle of translation
1 Codon recognition. The anticodon
TRANSCRIPTION
Amino end
of polypeptide
DNA
mRNA
Ribosome
of an incoming aminoacyl tRNA
base-pairs with the complementary
mRNA codon in the A site. Hydrolysis
of GTP increases the accuracy and
efficiency of this step.
TRANSLATION
Polypeptide
E
mRNA
Ribosome ready for
next aminoacyl tRNA
5
3
P A
site site
2
GTP
2 GDP
E
E
P
P
A
2 Peptide bond formation. An
GDP
3 Translocation. The ribosome
translocates the tRNA in the A
site to the P site. The empty tRNA
in the P site is moved to the E site,
where it is released. The mRNA
moves along with its bound tRNAs,
bringing the next codon to be
translated into the A site.
GTP
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A
E
P
A
rRNA molecule of the large
Subunit catalyzes the formation
of a peptide bond between the
new amino acid in the A site and
the carboxyl end of the growing
polypeptide in the P site. This step
attaches the polypeptide to the
tRNA in the A site.
Figure 17.19 The termination of translation
Release
factor
Free
polypeptide
5
3
3
3
5
5
Stop codon
(UAG, UAA, or UGA)
1 When a ribosome reaches a stop
2 The release factor hydrolyzes
codon on mRNA, the A site of the
ribosome accepts a protein called
a release factor instead of tRNA.
the bond between the tRNA in
the P site and the last amino
acid of the polypeptide chain.
The polypeptide is thus freed
from the ribosome.
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3 The two ribosomal subunits
and the other components of
the assembly dissociate.
Figure 17.20 Polyribosomes
Completed
polypeptide
Growing
polypeptides
Incoming
ribosomal
subunits
Start of
mRNA
(5 end)
End of
mRNA
(3 end)
(a) An mRNA molecule is generally translated simultaneously
by several ribosomes in clusters called polyribosomes.
Ribosomes
mRNA
0.1 µm
(b) This micrograph shows a large polyribosome in a prokaryotic
cell (TEM).
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Figure 17.21 The signal mechanism for targeting
proteins to the ER
1 Polypeptide
synthesis begins
on a free
ribosome in
the cytosol.
2 An SRP binds
to the signal
peptide, halting
synthesis
momentarily.
3 The SRP binds to a
receptor protein in the ER
membrane. This receptor
is part of a protein complex
(a translocation complex)
that has a membrane pore
and a signal-cleaving enzyme.
4 The SRP leaves, and
the polypeptide resumes
growing, meanwhile
translocating across the
membrane. (The signal
peptide stays attached
to the membrane.)
5 The signalcleaving
enzyme
cuts off the
signal peptide.
6 The rest of
the completed
polypeptide leaves
the ribosome and
folds into its final
conformation.
Ribosome
mRNA
Signal
peptide
Signalrecognition
particle
(SRP) SRP
receptor
CYTOSOL protein
Translocation
complex
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Signal
peptide
removed
ER
membrane
Protein
Figure 17.22 Coupled transcription and translation
in bacteria
RNA polymerase
DNA
mRNA
Polyribosome
RNA
polymerase
Direction of
transcription
0.25 m
DNA
Polyribosome
Polypeptide
(amino end)
Ribosome
mRNA (5 end)
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Figure 17.23 The molecular basis of sickle-cell
disease: a point mutation
Wild-type hemoglobin DNA
3
Mutant hemoglobin DNA
5
C
T
T
In the DNA, the
mutant template
strand has an A where
the wild-type template
has a T.
A
The mutant mRNA has
a U instead of an A in
one codon.
3
5
T
C
mRNA
A
mRNA
G
A
A
5
G
3
U
5
3
Normal hemoglobin
Sickle-cell hemoglobin
Glu
Val
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The mutant (sickle-cell)
hemoglobin has a valine
(Val) instead of a glutamic
acid (Glu).
Figure 17.24 Base-pair substitution
Wild type
mRNA
A U G A A G U U U G G C U A A
5
Protein
Met
Lys
3
Phe
Amino end
Gly
Stop
Carboxyl end
Base-pair substitution
No effect on amino acid sequence
U instead of C
A U G A A G U U U G G U U A A
Met
Lys
Missense
Phe
Gly
Stop
A instead of G
A U G A A G U U U A G U U A A
Met
Lys
Phe
Ser
Stop
Nonsense
U instead of A
A U G U A G U U U G G C U A A
Met
Stop
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Figure 17.25 Base-pair insertion or deletion
Wild type
mRNA 5
Protein
A UG A A GU U U GG C U A A
Met
Lys
Gly
Phe
3
Stop
Amino end
Carboxyl end
Base-pair insertion or deletion
Frameshift causing immediate nonsense
Extra U
A U GU A A G U U U GG C U A
Met
Stop
Frameshift causing
extensive missense
U Missing
A U G A A G U U G G C U A A
Met
Lys
Leu
Ala
Insertion or deletion of 3 nucleotides:
no frameshift but extra or missing amino acid
A A G Missing
A U G U U UG G C U A A
Met
Phe
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Gly
Stop
Figure 17.26 A summary of transcription and
translation in a eukaryotic cell
DNA
TRANSCRIPTION
1 RNA is transcribed
from a DNA template.
3
5
RNA
transcript
RNA
polymerase
RNA PROCESSING
Exon
2 In eukaryotes, the
RNA transcript (premRNA) is spliced and
modified to produce
mRNA, which moves
from the nucleus to the
cytoplasm.
RNA transcript
(pre-mRNA)
Intron
Aminoacyl-tRNA
synthetase
NUCLEUS
Amino
acid
tRNA
FORMATION OF
INITIATION COMPLEX
CYTOPLASM 3 After leaving the
nucleus, mRNA attaches
to the ribosome.
mRNA
AMINO ACID ACTIVATION
4
Each amino acid
attaches to its proper tRNA
with the help of a specific
enzyme and ATP.
Growing
polypeptide
Activated
amino acid
Ribosomal
subunits
5
TRANSLATION
A succession of tRNAs
add their amino acids to
the polypeptide chain
Anticodon
as the mRNA is moved
through the ribosome
one codon at a time.
(When completed, the
polypeptide is released
from the ribosome.)
5
E
A
AAA
UG GU U U A U G
Codon
Ribosome
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