Download Chapter 17 (Oct 23, 27, 28)

Chapter 17: From Gene to Protein
Important questions that were answered….
Chapter 13 – “What is the process of making gametes?” – meiosis
Chapter 14 – “How are traits passed along to offspring?” – gametes
Chapter 15 – “What carries the genetic material?” – chromosomes
Chapter 16 – “What is the genetic material?” – DNA
Chapter 17 – “How do genes give us our traits?”
Chapter 17: From Gene to Protein
1. What is the “Central Dogma of Molecular Biology”?
Transcription
DNA
Nucleotide lang.
Translation
RNA
Nucleotide lang.
Protein
aa lang.
2. How is this different in prokaryotes & eukaryotes?
Figure 17.3 Overview: the roles of transcription and translation in the flow of
genetic information
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
(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 5.26 Components of nucleic acids
Nitrogenous bases
Pyrimidines
5’ end
5’C
NH2
O
Nucleoside
O
Nitrogenous
base
O
O
5’C
O
3’C

C
CH
CH
5’C
O P O
Purines
CH2 O
O
Phosphate 3’C
Pentose
group
sugar
O
NH2
HC
N C C
N
N C
N
H
Adenine
A
(b) Nucleotide
OH
3’ end
(a) Polynucleotide,
or nucleic acid
O
C
C
CH3
HN
C
HN
CH
C
CH
C
C
CH
N
N
O
N
O
O
H
H
H
Cytosine Thymine (in DNA) Uracil (in RNA)
C
U
T
N
3’C
O
HC
N C N
H
Guanine
G
Pentose sugars
5’
HOCH2 O
4
H H
H
CH
N C C
NH
3’ 2’
OH
1’
H
OH H
Deoxyribose (in DNA)
C
NH2
5’
HOCH2 O OH
4
H H 1’
H 3’ 2’ H
OH OH
Ribose (in RNA)
(c) Nucleoside components
Chapter 17: From Gene to Protein
1. What is the “Central Dogma of Molecular Biology?
2. How is this different in prokaryotes & eukaryotes?
3. What are the stages of transcription?
- Initiation
- Elongation
- Termination
Chapter 17: From Gene to Protein
1. What is the “Central Dogma of Molecular Biology?
2. How is this different in prokaryotes & eukaryotes?
3. What are the stages of transcription?
TRANSCRIPTION
RNA PROCESSING
At promoter – promotes transcription
Transcription factors bind to TATA box
RNA polymerase makes RNA
Energy from ATP needed to start
Pre-mRNA
mRNA
TRANSLATION
- Initiation
-
1 Eukaryotic promoters
DNA
Ribosome
Polypeptide
Promoter
5
T A T A A AA
3
3
ATAT T T T
5
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
3
5
3
5
5
RNA transcript
Transcription initiation complex
Chapter 17: From Gene to Protein
1. What is the “Central Dogma of Molecular Biology?
2. How is this different in prokaryotes & eukaryotes?
3. What are the stages of transcription? Elongation
- Initiation
- Elongation
-
-
Bases added to 3’ end (-OH)
RNA polymerase – 60 nts/sec
opens DNA 10-20 bases at
a time
NTPs provide energy
Non-template
strand of DNA
RNA nucleotides
RNA
polymerase
3
A
T
C
C A A
3 end
U
5
A U G C A
T A G G T
5
T
Direction of transcription
(“downstream)
Newly made
RNA
Template
strand of DNA
Chapter 17: From Gene to Protein
1. What is the “Central Dogma of Molecular Biology?
2. How is this different in prokaryotes & eukaryotes?
3. What are the stages of transcription?
Promoter
Transcription unit
- Initiation
DNA
- Elongation
Start point
5
3
- Termination
-
RNA polymerase
3
5
1 Initiation. After RNA polymerase binds to
the promoter, the DNA strands unwind, and
the polymerase initiates RNA synthesis at the
start point on the template strand.
AAUAAA – stop sequence
10 – 35 bases later
5
3
3
5
Template strand
Unwound RNA of DNA
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
5
Completed RNA
transcript
3
Chapter 17: From Gene to Protein
1.
2.
3.
4.
What is the “Central Dogma of Molecular Biology?
How is this different in prokaryotes & eukaryotes?
What are the stages of transcription?
How is the mRNA altered (processed)?
- 5’ cap – modified Guanine added with a methyl group (-CH3)
- 3’ 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
Polypeptide
5 UTR
Start codon Stop codon
3 UTR
Poly-A tail
Chapter 17: From Gene to Protein
1.
2.
3.
4.
What is the “Central Dogma of Molecular Biology?
How is this different in prokaryotes & eukaryotes?
What are the stages of transcription?
How is the mRNA altered (processed)?
- 5’ cap
- 3’ poly-A tail
- Splicing exons together & removing introns
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
5 UTR
-
Splicing is done in a spliceosome
Poly-A tail
146
3 UTR
Figure 17.11 The roles of snRNPs & spliceosomes in pre-mRNA splicing
-snRNPs recognize short sequence in intron
-Intron is removed & exons joined
Chapter 17: From Gene to Protein
1.
2.
3.
4.
5.
What is the “Central Dogma of Molecular Biology?
How is this different in prokaryotes & eukaryotes?
What are the stages of transcription?
How is the mRNA altered (processed)?
How is the mRNA read to go from NA language to aa language?
- Triplet code – codon
- 3 bases = 1 aa
DNA
Gene 2
molecule
- Codons do not overlap
Gene 1
- Reading frame
- The red dog ate the cat.
Gene 3
- The red cat ate the dog.
- There dc ata tet hed og. DNA strand
3
A C C A A A C C G A
- “The Rosetta Stone of
(template)
Molecular Biology”
G T
5
TRANSCRIPTION
mRNA
5
U G G U U U G G C U C A
Codon
TRANSLATION
Protein
Trp
Amino acid
Phe
Gly
Ser
3
Figure 17.5 The dictionary of the genetic code
Second mRNA base
Let’s translate:
- UGG
- Trp
- ACC
- Thr
- GAA
- Glu
- AUG – start
- UAA, UAG, UGA – stop
UUU
UUC
U
UUA
C
A
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
GCG
Ala
His
Gln
Asn
AAA
AUGMet or ACG
start
G
G
UAA Stop UGA Stop A
UAG Stop UGG Trp G
UUG
First mRNA base (5 end)
- There is redundancy
- Only the 1st 2 bases matter
-(a.k.a. “wobble”
C
GAA
GAG
Lys
U
CGU
CGC
CGA
Arg
A
CGG
G
AGU
U
AGC
Ser C
AGA
A
AGG Arg G
U
GGU
Asp
Glu
C
GGC
GGA
GGG
Gly
C
A
G
Third mRNA base (3 end)
U
Chapter 17: From Gene to Protein
1.
2.
3.
4.
5.
6.
What is the “Central Dogma of Molecular Biology?
How is this different in prokaryotes & eukaryotes?
What are the stages of transcription?
How is the mRNA altered (processed)?
How is the mRNA read to go from NA language to aa language?
In what organelle does translation take place?
- Ribosome
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
Amino
acids
Polypeptide
tRNA with
amino acid
Ribosome attached
Gly
tRNA
A AA
UGGU UU GG C
Codons
5
mRNA
Anticodon
3
Chapter 17: From Gene to Protein
1.
2.
3.
4.
5.
6.
7.
What is the “Central Dogma of Molecular Biology?
How is this different in prokaryotes & eukaryotes?
What are the stages of transcription?
How is the mRNA altered (processed)?
How is the mRNA read to go from NA language to aa language?
Where does translation take place?
What does tRNA do?
- Transfers amino acids to protein being made
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
*
AG *
C A C AG UA
* CUC
G
*
C * * G U G UC*
C G A GA GG
U
G
*
* GAG C
G C Hydrogen
U A bonds
* G
A
*
A
C
*
U
A AG
Anticodon
5
3
Amino acid
attachment site
Hydrogen
bonds
A A G
3
Anticodon
Wobble – 3rd base doesn’t matter
Anticodon
5
Ribosomes are made of rRNA & proteins in the nucleolus (Ch 6)
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.
Chapter 17: From Gene to Protein
1.
2.
3.
4.
5.
6.
7.
8.
What is the “Central Dogma of Molecular Biology?
How is this different in prokaryotes & eukaryotes?
What are the stages of transcription?
How is the mRNA altered (processed)?
How is the mRNA read to go from NA language to aa language?
Where does translation take place?
What does tRNA do?
What are the steps of translation?
- Initiation
- Elongation
- Termination
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
mRNA binding site
1
Small subunit
mRNA
Initiator tRNA with Met
5
3
Small
ribosomal
subunit
3
Translation initiation complex
2
Energy from GTP allows large
subunit to bind
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.
A
GTP
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.
3 The two ribosomal subunits
and the other components of
the assembly dissociate.
Chapter 5 The Structure and Function of Macromolecules
9. How are all amino acids similar?
- Amino group (-NH2)
- Carboxyl group (-COOH)
- Variable “R” group
- C in the center
- H
 carbon
R
O
H
N
C
C
OH
H
H
Amino
group
Carboxyl
group
Figure 5.17 The 20 amino acids of proteins
CH3
CH3
H
H3N+
C
CH3
O
H3N+
C
H
Glycine (Gly)
O–
C
H3N+
C
H
Alanine (Ala)
O–
CH
CH3
CH3
O
C
CH2
CH2
O
H3N+
C
H
Valine (Val)
CH3
CH3
O–
C
O
H3N+
C
H
Leucine (Leu)
H3C
O–
CH
C
O
C
H
Isoleucine (Ile)
O–
Nonpolar
CH3
CH2
S
NH
CH2
CH2
H3N+
C
H
CH2
O
H3N+
C
O–
Methionine (Met)
C
H
CH2
O
H3N+
C
C
O–
Phenylalanine (Phe)
H
O
H2C
CH2
H2N
C
O
C
O–
H
C
O–
Tryptophan (Trp)
Proline (Pro)
Non-polar – equal sharing of electrons in these bonds of R-groups
OH
OH
Polar
CH2
H3N+
C
CH
O
H3N+
C
O–
H
Serine (Ser)
C
CH2
O
H3N+
C
O–
H
C
CH2
O
C
H
O–
H3N+
C
O
H3N+
C
O–
H
C
Electrically
charged
CH2
H3N+
C
O
H
H3N+
NH3+
O
C
C
O
C
O–
H
Glutamine
(Gln)
C
CH2
CH2
CH2
CH2
CH2
C
O
CH2
C
O–
H3N+
C
H
C
O–
Lysine (Lys)
NH2+
H3N+
CH2
O
CH2
H3N+
C
H
Glutamic acid
(Glu)
NH+
NH2
CH2
H
Aspartic acid
(Asp)
C
H3N+
–
O
C
CH2
C
O–
CH2
Basic
O–
O
O
Asparagine
(Asn)
Acidic
–O
CH2
CH2
H
Tyrosine
(Tyr)
Cysteine
(Cys)
Threonine (Thr)
C
NH2 O
C
SH
CH3
OH
NH2 O
NH
CH2
O
C C
O–
H
O
C
O–
Arginine (Arg)
Histidine (His)
10. Why are these polar? (Review in Ch 2 if needed)
- Electronegative atoms – O & N – attract & hold electrons
- Unequal sharing of electrons in R-groups where O & N are
11. Why acidic & basic?
- Acids – donate H+ to environment (H+ = proton)
- Bases – accept H+ from environment
Chapter 5 The Structure and Function of Macromolecules
9. How are all amino acids similar?
10. Why are these polar?
11. Why acidic & basic?
12. How are amino acids connected?
Dehydration (condensation) rxn
Creates a peptide bond (C—N)
Figure 5.18 Making a polypeptide chain
Peptide
bond
OH
CH2
SH
CH2
H
N
H
OH
C C
CH2
H
H
N C C OH H
N C
H O
H O
H
(a)
C OH
O
DESMOSOMES
H2O
OH
DESMOSOMES
DESMOSOMES
OH
CH2
H
H N C C
H O
(b)
Amino end
(N-terminus)
Side chains (R-groups)
SH
Peptide
CH2 bond CH2
H
H
N C C
H O
N C C
H O
Carboxyl end
(C-terminus)
OH
Backbone
Chapter 5 The Structure and Function of Macromolecules
9.
10.
11.
12.
13.
-
How are all amino acids similar?
Why are these polar?
Why acidic & basic?
How are amino acids connected?
What are the 4 levels of protein structure?
1° (Primary) – aa sequence (determined by DNA sequence)
2° (Secondary) – based on H-bonds
3° (Tertiary) – overall globular shape – 3D structure
4° (Quaternary) – several 3° polypeptides (subunits)
Figure 5.20 Primary structure of a protein
• Based on amino acid sequence
• Each protein has a unique sequence
• Like the alphabet (letters = aa)
– Order is important for proper function
• great
• grate
• retag
• arteg
Gly Pro Thr Gly
Thr
+H N
3
Amino acid
subunits
Gly
Amino end
Leu
Seu
Pro Cys Lys
Glu
Met
Val
Lys
Val
Leu
Asp
Ala Val Arg Gly
Ser
Pro
Ala
Glu Lle
Asp
Thr
Lys
Ser
Tyr
Lys Trp
Leu Ala
Gly
lle
Ser
Pro Phe
His Glu
His
Ala
Glu
Ala Thr Phe Val
Val
Asn
Asp
Arg
Ser
Gly Pro
Thr
Tyr
Thr
lle
Ala
Ala
Arg
Leu
Ser Tyr
Ser
Tyr Pro
Leu
Ser
Thr
Ala
Val
Val
Thr
Asn Pro
Lys Glu
c
o
o–
Carboxyl end
Figure 5.20 Secondary structure of a protein
 pleated
sheet
Amino
acid
subunits
H
O
O
H
R
C N
H
C C N
C
N
C
C
R
O H H
O
C
C
R
H
N
O
N
O
C
H C
H
O
R H C
R
H
O C
N
O
C
C
R
N
C
H
H
R
H
C
C
N
H
C C N
O H H
R
C
H
N HC N H C
H
C
O
R
C
H H
C C N
O
R
C C N
O H H
R
O
H
H
N H C N
C
H
C
O
R
C
C C
O
R
R
O
H
H
N H C N
C
H
C
O
R
H
C
N H C N
H
C
O
H
H
 helix
R H C R
H
O C
N
O
R
R
C
O
N
C
H C
C N
H H
C C N
O
H
R
R
O
H
C
R
N
C
H
H
Based on H-bonds
• α-helix
• adjacent polar aa (every 4th aa is polar)
- β-pleated sheet
- after folding, polar aa become neighbors
and form H-bonds
Hydrogen Bonds
• A hydrogen bond (Review in Ch 2 if needed)
– Occurs between 2 molecules with polar covalent bonds
– Forms when a hydrogen atom bonded to one
electronegative atom is also attracted to another
electronegative atom
–
+
H
Water
(H2O)
O
H
+
–
Ammonia
(NH3)
N
H
+
Figure 2.15
H
H
+
+
A hydrogen
bond results
from the
attraction
between the
partial positive
charge on the
hydrogen atom
of water and
the partial
negative charge
on the nitrogen
atom of
ammonia.
Figure 5.20 Tertiary structure
• overall globular shape – 3D structure
• each protein has unique 3D shape
• based on 1° structure (aa sequence)
• Disulfide bridge--2 cysteine amino acids
-(a type of covalent bond)
• hydrophobic interactions
• ionic bonds
• occasional H-bonds
CH
CH2
Hydrogen
bond
H3C
CH3
H3C
CH3
CH
O
H
O
Hydrophobic
interactions and
van der Waals
interactions
OH C
CH2
CH2 S S CH2
Disulfide bridge
O
CH2 NH3+ -O C CH2
Ionic bond
Polypeptide
backbone
Figure 5.20 Quaternary structure
• more than one 3° polypeptide (subunit) needed for
biological activity
• not all proteins have quaternary structure
• # of subunits varies by protein
Polypeptide
chain
Collagen
 Chains
Iron
Heme
 Chains
Hemoglobin
Chapter 5 The Structure and Function of Macromolecules
13. What are the 4 levels of protein structure?
14. How does structure (sequence) influence function?
- Sickle cell anemia
Figure 5.21 A single amino acid substitution in a protein
causes sickle-cell disease
Primary
structure
Normal hemoglobin
Val
His
Leu
Glu
Glu
Sickle-cell hemoglobin
Val
His
Leu


Molecules do
not associate
with one
another; each
carries oxygen
Normal cells are
full of individual
hemoglobin
molecules, each
carrying oxygen


Thr
Pro
Val
Glu
...
structure 1 2 3 4 5 6 7
Secondary
 subunit and tertiary
structures
Quaternary Hemoglobin A
structure
Red blood
cell shape
Pro
1 2 3 4 5 6 7
Secondary
and tertiary
structures
Function
Thr
. . . Primary
Quaternary
structure
 subunit




Function
10 m
10 m
Red blood
cell shape
Hemoglobin S
Molecules
interact with
one another to
crystallize into a
fiber, capacity to
carry oxygen is
greatly reduced
Fibers of abnormal
hemoglobin deform
cell into sickle
shape
Chapter 5 The Structure and Function of Macromolecules
13. What are the 4 levels of protein structure?
14. How does structure (sequence) influence function?
15. What are polyribosomes?
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).
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)
Chapter 17: From Gene to Protein
13. What are the 4 levels of protein structure?
14. How does structure (sequence) influence function?
15. What are polyribosomes?
16. How is rough ER made?
- SRP
- signal recognition particle
- Binds to signal peptide (1st couple amino acids)
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
Signal
peptide
removed
Translocation
complex
Which proteins are made in rough ER?
- Secreted from cell or stay outside of cell
- Embedded in plasma membrane
ER
membrane
Protein
Chapter 17: From Gene to Protein
13. What are the 4 levels of protein structure?
14. How does structure (sequence) influence function?
15. What are polyribosomes?
16. How is rough ER made?
17. How do mutations alter the genotype & phenotype of organisms?
- Mutation – any change in the genetic material of a cell (heritable)
- Point mutation – a change in 1 or only a few bases
- Base-pair substitution
- Insertions or deletions result in a frameshift
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
Silent mutation - No change in aa
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
Missense – still translates but a
mistake is made
Nonsense – stop codon created
NO complete protein
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
Gly
Stop
Frameshift – reading frame is shifted
creating new codons
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