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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 17
From Gene to Protein
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: The Flow of Genetic Information
• The information content of DNA is in the form of
specific sequences of _____________________
• The DNA inherited by an organism leads to
specific traits by dictating the synthesis of
_____________________
• _______________ are the links between
genotype and phenotype
• _________________, the process by which DNA
directs protein synthesis, includes two stages:
_________________ and __________________
© 2011 Pearson Education, Inc.
Concept 17.1: Genes specify proteins via
transcription and translation
• How was the fundamental relationship between
genes and proteins discovered?
© 2011 Pearson Education, Inc.
Evidence from the Study of Metabolic
Defects
• In 1902, British physician Archibald _________
first suggested that _______ dictate ___________
through enzymes that catalyze specific chemical
reactions
• He thought symptoms of an inherited disease
reflect an inability to synthesize a certain _______
• _____________________________ required
understanding that cells synthesize and degrade
molecules in a series of steps, a metabolic
pathway
© 2011 Pearson Education, Inc.
Nutritional Mutants in Neurospora:
Scientific Inquiry
• George ___________ and Edward__________
exposed bread mold to X-rays, creating mutants
that were unable to survive on minimal media
• Using crosses, they and their coworkers identified
three classes of ______________________, each
lacking a different enzyme necessary for
synthesizing arginine
• They developed a _________________________,
which states that each gene dictates production of
a specific enzyme
© 2011 Pearson Education, Inc.
Figure 17.2a
EXPERIMENT
Growth:
Wild-type
cells growing
and dividing
No growth:
Mutant cells
cannot grow
and divide
Minimal medium
Figure 17.2b
RESULTS
Classes of Neurospora crassa
Wild type
Minimal
medium
(MM)
(control)
Growth
Class I mutants Class II mutants Class III mutants
No
growth
Condition
MM 
ornithine
MM 
citrulline
MM 
arginine
(control)
Summary
of results
Can grow with
or without any
supplements
Can grow on
ornithine,
citrulline, or
arginine
Can grow only
on citrulline or
arginine
Require arginine
to grow
Figure 17.2c
CONCLUSION
Gene
(codes for
enzyme)
Gene A
Gene B
Gene C
Class II mutants Class III mutants
(mutation in
(mutation in
gene B)
gene C)
Wild type
Class I mutants
(mutation in
gene A)
Precursor
Precursor
Precursor
Precursor
Enzyme A
Enzyme A
Enzyme A
Enzyme A
Ornithine
Ornithine
Ornithine
Ornithine
Enzyme B
Enzyme B
Enzyme B
Enzyme B
Citrulline
Citrulline
Citrulline
Citrulline
Enzyme C
Enzyme C
Enzyme C
Enzyme C
Arginine
Arginine
Arginine
Arginine
The Products of Gene Expression:
A Developing Story
• Some proteins aren’t enzymes, so researchers
later revised the hypothesis: ______________
_____________________
• Many proteins are composed of several
polypeptides, each of which has ____________
• Therefore, Beadle and Tatum’s hypothesis is
now restated as the _____________________
___________________
• Note that it is common to refer to gene products
as ___________ rather than _______________
© 2011 Pearson Education, Inc.
Basic Principles of Transcription and
Translation
• ____________ is the bridge between genes
and the proteins for which they code
• ___________________ is the synthesis of
RNA using information in DNA
• Transcription produces __________________
________________
• __________________ is the synthesis of a
polypeptide, using information in the mRNA
• ________________ are the sites of translation
© 2011 Pearson Education, Inc.
• In prokaryotes, translation of mRNA can begin
_____________________________________
• In a eukaryotic cell, the _____________________
separates transcription from translation
• Eukaryotic RNA transcripts are modified through
_________________ to yield the finished mRNA
© 2011 Pearson Education, Inc.
• A ____________________ is the initial RNA
transcript from any gene prior to processing
• The central dogma is the concept that cells are
governed by a cellular chain of command:
__________________________
© 2011 Pearson Education, Inc.
Figure 17.UN01
DNA
RNA
Protein
Figure 17.3a-2
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
(a) Bacterial cell
Figure 17.3b-3
Nuclear
envelope
TRANSCRIPTION
RNA PROCESSING
DNA
Pre-mRNA
mRNA
TRANSLATION
Ribosome
Polypeptide
(b) Eukaryotic cell
The Genetic Code
• How are the instructions for assembling amino
acids into proteins encoded into DNA?
• There are ________________, but there are only
_____________________ in DNA
• How many nucleotides correspond to an
amino acid?
© 2011 Pearson Education, Inc.
Codons: Triplets of Nucleotides
• The flow of information from gene to protein is
based on a ___________________: a series of
nonoverlapping, three-nucleotide words
• The words of a gene are ___________________
into complementary nonoverlapping threenucleotide words of mRNA
• These words are then ______________ into a
chain of amino acids, forming a ______________
© 2011 Pearson Education, Inc.
Figure 17.4
DNA
template
strand
5
3
A C C
A A
A C
T
T
T
G G
T
C G A G
G G C
T
T
C A
3
5
DNA
molecule
Gene 1
TRANSCRIPTION
Gene 2
U G G
mRNA
U U
U G G C U
C A
5
3
Codon
TRANSLATION
Protein
Trp
Phe
Gly
Ser
Gene 3
Amino acid
• During transcription, one of the two DNA strands,
called the _______________________, provides
a template for ordering the sequence of
complementary nucleotides in an RNA transcript
• The template strand is always the ____________
_____________________________
• During translation, the mRNA base triplets, called
____________, are read in the _______ direction
© 2011 Pearson Education, Inc.
• Codons along an mRNA molecule are read by
translation machinery in the _________ direction
• Each ________ specifies the _____________
(one of 20) to be placed at the corresponding
position along a polypeptide
© 2011 Pearson Education, Inc.
Cracking the Code
• All ________were deciphered by the mid-1960s
• Of the 64 triplets, 61 code for ______________;
3 triplets are “_______” signals to end translation
• The genetic code is ______________(more than
one codon may specify a particular amino acid)
but not ambiguous; no codon specifies more
than one amino acid
• Codons must be read in the correct ______
___________(correct groupings) in order for the
specified polypeptide to be produced
© 2011 Pearson Education, Inc.
Figure 17.5
Second mRNA base
UUU
U
UUC
First mRNA base (5 end of codon)
UUA
C
Phe
Leu
UAU
UCC
UAC
UCA
Ser
Tyr
UGU
UGC
Cys
U
C
UAA Stop UGA Stop A
UCG
UAG Stop UGG Trp G
CUU
CCU
CAU
CUC
CCC
CAC
Leu
CCA
Pro
CAA
CUG
CCG
CAG
AUU
ACU
AAU
ACC
AAC
AUC
Ile
AUA
AUG
G
UCU
G
UUG
CUA
A
A
C
ACA
Met or
start
Thr
AAA
His
Gln
Asn
Lys
CGU
U
CGC
C
CGA
Arg
CGG
AGU
G
Ser
AGC
AGA
A
Arg
U
C
A
ACG
AAG
AGG
G
GUU
GCU
GAU
GGU
U
GUC
GCC
GAC
GGC
C
GAA
GGA
GUA
GUG
Val
GCA
GCG
Ala
GAG
Asp
Glu
GGG
Gly
A
G
Third mRNA base (3 end of codon)
U
Evolution of the Genetic Code
• The genetic code is _______________, shared by
the simplest bacteria to the most complex animals
• Genes can be transcribed and translated _____
___________________from one species to
another
© 2011 Pearson Education, Inc.
Figure 17.6
(a) Tobacco plant expressing
a firefly gene
(b) Pig expressing a jellyfish
gene
Concept 17.2: Transcription is the DNAdirected synthesis of RNA: a closer look
• ____________is the first stage of gene expression
© 2011 Pearson Education, Inc.
Molecular Components of Transcription
• RNA synthesis is catalyzed by _______________,
which pries the DNA strands apart and hooks
together the RNA nucleotides
• The RNA is ______________to the DNA template
strand
• RNA synthesis follows the same base-pairing
rules as DNA, except that __________substitutes
for _________________
© 2011 Pearson Education, Inc.
• The DNA sequence where RNA polymerase
attaches is called the _______________; in
bacteria, the sequence signaling the end of
transcription is called the _______________
• The stretch of DNA that is transcribed is called a
_______________________
© 2011 Pearson Education, Inc.
Figure 17.7-4
Promoter
Transcription unit
5
3
Start point
RNA polymerase
3
5
DNA
1 Initiation
Nontemplate strand of DNA
3
5
5
3
Unwound
DNA
RNA
transcript
Template strand of DNA
2 Elongation
Rewound
DNA
5
3
3
5
3
5
RNA
transcript
3 Termination
3
5
5
3
5
Completed RNA transcript
3
Direction of transcription (“downstream”)
Synthesis of an RNA Transcript
• The three stages of transcription
– ____________________
– ____________________
– ____________________
© 2011 Pearson Education, Inc.
RNA Polymerase Binding and Initiation of
Transcription
• _______________ signal the transcriptional
___________ and usually extend several dozen
nucleotide pairs upstream of the start point
• _____________________ mediate the binding of
RNA polymerase and the initiation of transcription
• The completed assembly of transcription factors
and _________________bound to a promoter is
called a _______________________
• A promoter called a ______________is crucial in
forming the initiation complex in eukaryotes
© 2011 Pearson Education, Inc.
Figure 17.8
1 A eukaryotic promoter
Promoter
Nontemplate strand
DNA
5
3
3
5
T A T A A AA
A T AT T T T
TATA box
Transcription
factors
Start point
Template strand
2 Several transcription
factors bind to DNA
5
3
3
5
3 Transcription initiation
complex forms
RNA polymerase II
Transcription factors
5
3
5
3
RNA transcript
Transcription initiation complex
3
5
Elongation of the RNA Strand
• As __________________ moves along the DNA,
it untwists the double helix, 10 to 20 bases at a
time
• Transcription progresses at a rate of ______
nucleotides per second in eukaryotes
• A gene can be transcribed simultaneously by
_______________________
• Nucleotides are added to the ________ of the
growing RNA molecule
© 2011 Pearson Education, Inc.
Figure 17.9
Nontemplate
strand of DNA
RNA nucleotides
RNA
polymerase
A
3
T
C
C
A A
5
3 end
C A
U
C
C A
T
A
G
G T
5
5
C
3
T
Direction of transcription
Template
strand of DNA
Newly made
RNA
Termination of Transcription
• The mechanisms of _________________ are
different in bacteria and eukaryotes
• In ________________, the polymerase stops
transcription at the end of the _______________
and the mRNA can be translated without further
modification
• In ______________, RNA polymerase II
transcribes the ___________________________;
the RNA transcript is released ___________
nucleotides past this polyadenylation
sequence
© 2011 Pearson Education, Inc.
Concept 17.3: Eukaryotic cells modify RNA
after transcription
• Enzymes in the eukaryotic nucleus modify premRNA (_______________) before the genetic
messages are dispatched to the cytoplasm
• During RNA processing, both ends of the
primary transcript are usually ____________
• Also, usually some interior parts of the molecule
are _______, and the other parts ____________
____________________
© 2011 Pearson Education, Inc.
Alteration of mRNA Ends
• Each end of a pre-mRNA molecule is modified
in a particular way
– The 5 end receives a modified nucleotide
_______
– The 3 end gets a _______________
• These modifications share several functions
– They seem to facilitate the ________________
to the cytoplasm
– They ______________from hydrolytic enzymes
– They help ___________________to the 5 end
© 2011 Pearson Education, Inc.
Figure 17.10
5
G
Protein-coding
segment
P P P
5 Cap 5 UTR
Polyadenylation
signal
AAUAAA
Start
codon
Stop
codon
3 UTR
3
AAA … AAA
Poly-A tail
Split Genes and RNA Splicing
• Most eukaryotic genes and their RNA transcripts
have long ____________________of nucleotides
that lie between coding regions
• These noncoding regions are called intervening
sequences, or ____________
• The other regions are called ____________
because they are eventually expressed, usually
translated into amino acid sequences
• _____________________removes introns and
joins exons, creating an mRNA molecule with a
continuous coding sequence
© 2011 Pearson Education, Inc.
Figure 17.11
5 Exon Intron Exon
Pre-mRNA 5 Cap
Codon
130
31104
numbers
Intron
Exon 3
Poly-A tail
105
146
Introns cut out and
exons spliced together
mRNA 5 Cap
Poly-A tail
1146
5 UTR
Coding
segment
3 UTR
• In some cases, RNA splicing is carried out by
________________
• _________________ consist of a variety of
proteins and several small _________________
_______________that recognize the splice sites
© 2011 Pearson Education, Inc.
Figure 17.12-3
RNA transcript (pre-mRNA)
5
Exon 1
Intron
Protein
snRNA
Exon 2
Other
proteins
snRNPs
Spliceosome
5
Spliceosome
components
5
mRNA
Exon 1
Exon 2
Cut-out
intron
Ribozymes
• ______________ are catalytic RNA molecules
that function as enzymes and can splice RNA
• The discovery of ribozymes rendered
______________the belief that all biological
catalysts were proteins
© 2011 Pearson Education, Inc.
• Three properties of RNA enable it to function
as an enzyme
– It can form a three-dimensional structure
because of its ability to ___________________
– Some bases in RNA contain functional groups
that may ________________________
– RNA may _______________________ with other
nucleic acid molecules
© 2011 Pearson Education, Inc.
The Functional and Evolutionary Importance
of Introns
• Some introns contain sequences that may
________________________________
• Some genes can encode _________________
_________________, depending on which
segments are treated as exons during splicing
• This is called __________________________
• Consequently, the number of different proteins an
organism can produce is ______________ than
its number of genes
© 2011 Pearson Education, Inc.
• Proteins often have a modular architecture
consisting of discrete regions called ________
• In many cases, _______________code for the
different domains in a protein
• __________________may result in the evolution
of new proteins
© 2011 Pearson Education, Inc.
Figure 17.13
Gene
DNA
Exon 1 Intron Exon 2 Intron Exon 3
Transcription
RNA processing
Translation
Domain 3
Domain 2
Domain 1
Polypeptide
Concept 17.4: Translation is the RNAdirected synthesis of a polypeptide: a
closer look
• Genetic information flows from mRNA to protein
through the process of __________________
© 2011 Pearson Education, Inc.
Molecular Components of Translation
• A cell translates an mRNA message into protein
with the help of _________________________
• _____________ transfer amino acids to the
growing polypeptide in a ribosome
• ___________________ is a complex process in
terms of its biochemistry and mechanics
© 2011 Pearson Education, Inc.
Figure 17.14
Amino
acids
Polypeptide
Ribosome
tRNA with
amino acid
attached
tRNA
C
G
Anticodon
U G G U U U G G C
5
Codons
mRNA
3
The Structure and Function of Transfer RNA
• Molecules of tRNA are ________________
– Each carries a _________________ on one end
– Each has an _________________ on the other
end; the anticodon base-pairs with a
complementary codon on mRNA
© 2011 Pearson Education, Inc.
• A tRNA molecule consists of a single RNA
strand that is only about ____nucleotides long
• Flattened into one plane to reveal its base
pairing, a tRNA molecule looks like a
____________
© 2011 Pearson Education, Inc.
Figure 17.15a
3
Amino acid
attachment
site
5
Hydrogen
bonds
Anticodon
(a) Two-dimensional structure
• Because of _______________, tRNA actually
twists and folds into a three-dimensional
molecule
• tRNA is roughly ________________
© 2011 Pearson Education, Inc.
Figure 17.15b
Amino acid
attachment
site
5
3
Hydrogen
bonds
A A G
3
Anticodon
(b) Three-dimensional structure
5
Anticodon
(c) Symbol used
in this book
• Accurate translation requires two steps
– First: a correct match between a tRNA and an
amino acid, done by the enzyme _____________
______________________
– Second: a correct match between the _______
_______________and an _________________
• Flexible pairing at the third base of a codon is
called ______________and allows some tRNAs
to bind to more than one codon
© 2011 Pearson Education, Inc.
Figure 17.16-4
Aminoacyl-tRNA
synthetase (enzyme)
Amino acid
P Adenosine
P P P Adenosine
P Pi
ATP
Pi
Pi
tRNA
Aminoacyl-tRNA
synthetase
tRNA
Amino
acid
P Adenosine
AMP
Computer model
Aminoacyl tRNA
(“charged tRNA”)
Ribosomes
• _______________facilitate specific coupling of
tRNA anticodons with mRNA codons in protein
synthesis
• The __________ ribosomal subunits (large and
small) are made of proteins and ______________
_____________________
• Bacterial and eukaryotic ribosomes are somewhat
similar but have significant differences: some
__________________specifically target bacterial
ribosomes without harming eukaryotic ribosomes
© 2011 Pearson Education, Inc.
Figure 17.17a
tRNA
molecules
Growing
polypeptide
Exit tunnel
Large
subunit
E P
A
Small
subunit
5
mRNA
3
(a) Computer model of functioning ribosome
Figure 17.17b
P site (Peptidyl-tRNA
binding site)
Exit tunnel
A site (AminoacyltRNA binding site)
E site
(Exit site)
E
mRNA
binding site
P
A
Large
subunit
Small
subunit
(b) Schematic model showing binding sites
Figure 17.17c
Growing polypeptide
Amino end
Next amino
acid to be
added to
polypeptide
chain
E
tRNA
mRNA
5
3
Codons
(c) Schematic model with mRNA and tRNA
• A ribosome has three binding sites for tRNA
– The ___________holds the tRNA that carries the
growing polypeptide chain
– The ___________holds the tRNA that carries the
next amino acid to be added to the chain
– The ___________is the exit site, where
discharged tRNAs leave the ribosome
© 2011 Pearson Education, Inc.
Building a Polypeptide
• The three stages of translation
– _______________
– _______________
– _______________
• All three stages require protein “__________” that
aid in the translation process
© 2011 Pearson Education, Inc.
Ribosome Association and Initiation of
Translation
• The _______________of translation brings
together mRNA, a tRNA with the first amino acid,
and the two ribosomal subunits
• First, a ________________binds with mRNA
and a special initiator tRNA
• Then the small subunit moves along the mRNA
until it reaches the ________________________
• Proteins called ________________bring in the
large subunit that completes the translation
initiation complex
© 2011 Pearson Education, Inc.
Figure 17.18
Large
ribosomal
subunit
3 U A C 5
5 A U G 3
P site
Pi
Initiator
tRNA

GTP
GDP
E
mRNA
5
Start codon
mRNA binding site
3
Small
ribosomal
subunit
5
A
3
Translation initiation complex
Elongation of the Polypeptide Chain
• During the ______________, amino acids are
added one by one to the preceding amino acid at
the _______________of the growing chain
• Each addition involves proteins called
______________________and occurs in three
steps: _________________________________
_______________________________________
• Translation proceeds along the mRNA in a _____
__________ direction
© 2011 Pearson Education, Inc.
Figure 17.19-4
Amino end of
polypeptide
E
3
mRNA
Ribosome ready for
next aminoacyl tRNA
P A
site site
5
GTP
GDP  P i
E
E
P A
P A
GDP  P i
GTP
E
P A
Termination of Translation
• Termination occurs when a ___________in the
mRNA reaches the ___________of the
ribosome
• The A site accepts a protein called a _________
_______________
• The release factor causes the addition of a
___________molecule instead of an amino acid
• This reaction releases the ______________,
and the translation assembly then
____________
© 2011 Pearson Education, Inc.
Figure 17.20-3
Release
factor
Free
polypeptide
5
3
3
5
5
Stop codon
(UAG, UAA, or UGA)
2
GTP
2 GDP  2 P i
3
Polyribosomes
• A number of ribosomes can translate a single
mRNA simultaneously, forming a _____________
(or _______________)
• Polyribosomes enable a cell to make
___________ ______________of a polypeptide
very quickly
© 2011 Pearson Education, Inc.
Figure 17.21
Growing
polypeptides
Completed
polypeptide
Incoming
ribosomal
subunits
Start of
mRNA
(5 end)
(a)
End of
mRNA
(3 end)
Ribosomes
mRNA
(b)
0.1 m
Completing and Targeting the Functional
Protein
• Often translation is ___________________to
make a functional protein
• Polypeptide chains are ___________________or
targeted to specific sites in the cell
© 2011 Pearson Education, Inc.
Protein Folding and Post-Translational
Modifications
• During and after synthesis, a polypeptide chain
spontaneously ________________into its threedimensional shape
• Proteins may also require ______________
________________before doing their job
• Some polypeptides are activated by _________
that cleave them
• Other polypeptides come together to form the
______________of a protein
© 2011 Pearson Education, Inc.
Targeting Polypeptides to Specific Locations
• Two populations of ribosomes are evident in cells:
_____________ (in the cytosol) and ________
__________________(attached to the ER)
• Free ribosomes mostly synthesize proteins that
function in the ____________
• Bound ribosomes make proteins of the
endomembrane system and proteins that are
________________________
• Ribosomes are ___________and can
___________ from free to bound
© 2011 Pearson Education, Inc.
• Polypeptide synthesis always begins in the
________________
• Synthesis finishes in the cytosol unless the
polypeptide signals the ribosome to
___________ _____________
• Polypeptides destined for the ER or for
secretion are marked by a ________________
© 2011 Pearson Education, Inc.
• A ________________binds to the signal peptide
• The SRP brings the signal peptide and its
ribosome to the _______
© 2011 Pearson Education, Inc.
Figure 17.22
1 Ribosome
5
4
mRNA
Signal
peptide
3
SRP
2
ER
LUMEN
SRP
receptor
protein
Translocation
complex
Signal
peptide
removed
ER
membrane
Protein
6
CYTOSOL
Concept 17.5: Mutations of one or a few
nucleotides can affect protein structure and
function
• ________________ are changes in the genetic
material of a cell or virus
• ________________are chemical changes in just
one base pair of a gene
• The change of a single nucleotide in a DNA
template strand can lead to the production of an
____________________
© 2011 Pearson Education, Inc.
Figure 17.23
Wild-type hemoglobin
Sickle-cell hemoglobin
Wild-type hemoglobin DNA
C T T
3
5
G A A
5
3
Mutant hemoglobin DNA
C A T
3
G T A
5
mRNA
5
5
3
mRNA
G A A
Normal hemoglobin
Glu
3
5
G U A
Sickle-cell hemoglobin
Val
3
Types of Small-Scale Mutations
• _______________within a gene can be divided
into two general categories
– ___________________
– One or more nucleotide-pair _______________
_______________
© 2011 Pearson Education, Inc.
Substitutions
• A _______________________replaces one
nucleotide and its partner with another pair of
nucleotides
• __________________ have no effect on the
amino acid produced by a codon because of
redundancy in the genetic code
• __________________ still code for an amino
acid, but not the correct amino acid
• __________________ change an amino acid
codon into a stop codon, nearly always leading
to a nonfunctional protein
© 2011 Pearson Education, Inc.
Figure 17.24a
Wild type
DNA template strand 3 T A C T T C A A A C C G A T T 5
5 A T G A A G T
T G G C
T
T A A 3
mRNA5 A U G A A G U U U G G C U A A 3
Protein
Met
Lys
Phe
Gly
Stop
Amino end
Carboxyl end
(a) Nucleotide-pair substitution: silent
A instead of G
3 T A C T T C A A A C C A A T T 5
5 A T G A A G T T T G G T T A A 3
U instead of C
5 A U G A A G U U U G G U U A A 3
Met
Lys
Phe
Gly
Stop
Figure 17.24b
Wild type
DNA template strand 3 T A C T T C A A A C C G A T T 5
5 A T G A A G T
T
T G G C
T A A 3
mRNA5 A U G A A G U U U G G C U A A 3
Protein
Met
Lys
Phe
Gly
Stop
Amino end
Carboxyl end
(a) Nucleotide-pair substitution: missense
T instead of C
3 T A C T T C A A A T C G A T T 5
5 A T G A A G T T T A G C T A A 3
A instead of G
5 A U G A A G U U U A G C U A A 3
Met
Lys
Phe
Ser
Stop
Figure 17.24c
Wild type
DNA template strand 3 T A C T T C A A A C C G A T T 5
5 A T G A A G T
T
T G G C
T A A 3
mRNA5 A U G A A G U U U G G C U A A 3
Protein
Met
Lys
Phe
Gly
Stop
Amino end
Carboxyl end
(a) Nucleotide-pair substitution: nonsense
A instead of T
T instead of C
3 T A C A T C A A A C C G A T T 5
5 A T G T A G T T T G G C T A A 3
U instead of A
5 A U G U A G U U U G G C U A A 3
Met
Stop
Insertions and Deletions
• ______________and ______________are
additions or losses of nucleotide pairs in a gene
• These mutations have a __________________on
the resulting protein more often than substitutions
do
• Insertion or deletion of nucleotides may alter the
reading frame, producing a __________________
© 2011 Pearson Education, Inc.
Figure 17.24d
Wild type
DNA template strand 3 T A C T T C A A A C C G A T T 5
5 A T G A A G T
T
T G G C T A A 3
mRNA5 A U G A A G U U U G G C U A A 3
Protein
Met
Amino end
Lys
Phe
Gly
Stop
Carboxyl end
(b) Nucleotide-pair insertion or deletion: frameshift causing
immediate nonsense
Extra A
3 T A C A T T C A A A C G G A T T 5
5 A T G T A A G T T T G G C T A A 3
Extra U
5 A U G U A A G U U U G G C U A A 3
Met
Stop
1 nucleotide-pair insertion
Figure 17.24e
Wild type
DNA template strand 3 T A C T T C A A A C C G A T T 5
5 A T G A A G T
T G G C
T
T A A 3
mRNA5 A U G A A G U U U G G C U A A 3
Protein
Met
Lys
Phe
Gly
Amino end
Stop
Carboxyl end
(b) Nucleotide-pair insertion or deletion: frameshift causing
extensive missense
A missing
3 T A C T T C A A C C G A T T 5
5 A T G A A G T T G G C T A A 3
U missing
5 A U G A A G U U G G C U A A
Met
Lys
1 nucleotide-pair deletion
Leu
Ala
3
Figure 17.24f
Wild type
DNA template strand 3 T A C T T C A A A C C G A T T 5
5 A T G A A G T
T
T G G C
T A A 3
mRNA5 A U G A A G U U U G G C U A A 3
Protein
Met
Gly
Lys
Phe
Stop
Carboxyl end
Amino end
(b) Nucleotide-pair insertion or deletion: no frameshift, but one
amino acid missing
T T C missing
3 T A C
5 A T G
A A A C C G A T T 5
T T T G G C T A A 3
A A G missing
5 A U G
Met
U U U G G C U A A 3
Phe
3 nucleotide-pair deletion
Gly
Stop
Mutagens
• ________________ can occur during DNA
replication, recombination, or repair
• _________________are physical or chemical
agents that can cause mutations
© 2011 Pearson Education, Inc.
Concept 17.6: While gene expression differs
among the domains of life, the concept of a
gene is universal
• _____________________, but share many
features of gene expression with eukaryotes
© 2011 Pearson Education, Inc.
Comparing Gene Expression in Bacteria,
Archaea, and Eukarya
• Bacteria and eukarya differ in their RNA
polymerases, termination of transcription,
and ribosomes; ____________ tend to
resemble eukarya in these respects
• Bacteria can ________________transcribe and
translate the same gene
• In eukarya, transcription and translation are
separated by the _________________
• In archaea, transcription and translation are
likely ______________
© 2011 Pearson Education, Inc.
Figure 17.25
RNA polymerase
DNA
mRNA
Polyribosome
RNA
polymerase
Direction of
transcription
0.25 m
DNA
Polyribosome
Polypeptide
(amino end)
Ribosome
mRNA (5 end)
What Is a Gene? Revisiting the Question
• The idea of the gene has ______________
through the history of genetics
• We have considered a gene as
– A discrete unit of __________________
– A region of _________________in a chromosome
– A DNA sequence that codes for a
___________________________________
© 2011 Pearson Education, Inc.
Figure 17.26
DNA
TRANSCRIPTION
3
5
RNA
polymerase
RNA
transcript
Exon
RNA
PROCESSING
RNA transcript
(pre-mRNA)
AminoacyltRNA synthetase
Intron
NUCLEUS
Amino
acid
AMINO ACID
ACTIVATION
tRNA
CYTOPLASM
mRNA
Growing
polypeptide
3
A
Aminoacyl
(charged)
tRNA
P
E
Ribosomal
subunits
TRANSLATION
E
A
Anticodon
Codon
Ribosome
• In summary, a ___________can be defined as a
region of DNA that can be expressed to produce
a final functional product, either a polypeptide
or an RNA molecule
© 2011 Pearson Education, Inc.