transcription translation
DESCRIPTION
Transcription Translation. Gene expression. - process by which DNA directs protein synthesis two stages :. transcription and translation. Figure 14.UN01. Central Dogma. Protein. RNA. DNA. Gene expression. Differences Between DNA and RNA. Prokaryotes. Figure 14.4a-2. - PowerPoint PPT PresentationTRANSCRIPT
TRANSCRIPTION TRANSLATION
GENE EXPRESSION-process by which DNA directs protein synthesis two stages:
transcription and translation
CENTRAL DOGMA
Gene expression
DNA RNA Protein
DIFFERENCES BETWEEN DNA AND RNA
PROKARYOTEStranslation of mRNA can begin before transcription has finished
FIGURE 14.4A-2
mRNA
DNATRANSCRIPTION
TRANSLATION
Polypeptide
Ribosome
(a) Bacterial cell
EUKARYOTES-the nuclear envelope
separates transcription from translation; mRNA must be transported out of the nucleus to be translated
Eukaryotic RNA transcripts are modified through RNA processing to yield the finished mRNA
FIGURE 14.4B-3
Nuclearenvelope
Pre-mRNA
mRNA
DNA
RNA PROCESSING
TRANSCRIPTION
TRANSLATION
Polypeptide
Ribosome
(b) Eukaryotic cell
Overview:http://www.pbslearningmedia.org/asset/lsps07_int_celltrans/
FIGURE 14.5
DNAtemplatestrand
Protein
mRNA
3
Trp
TRANSCRIPTION
TRANSLATION
Amino acid
Codon
5
35
3
5
Phe Gly Ser
GU G U UU G G UC C A
CA C A AA C C AG G T
GT G T TT G G TC C A
GENETIC CODE
FIGURE 14.6
UUU
Second mRNA base
UUC
UUA
UUG
UCU
UCC
UCA
UCG
UAU
UAC
UAA
UAG
UGU
UGC
UGA
UGG
CUU
CUC
CUA
CUG
CCU
CCC
CCA
CCG
CAU
CACCAA
CAG
CGU
CGCCGA
CGG
AUU
AUC
AUA
AUG
ACU
ACC
ACA
ACG
AAU
AAC
AAA
AAG
AGU
AGC
AGA
AGG
GUU
GUC
GUA
GUG
GCU
GCC
GCA
GCG
GAU
GACGAA
GAG
GGU
GGCGGA
GGG
Firs
t mR
NA
base
(5
end
of c
odon
)
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
U C A G
Phe
LeuSer
Tyr Cys
Trp
Met orstart
Stop
Stop Stop
ArgGln
His
ProLeu
Val Ala
Asp
GluGly
IIeThr
Lys
Asn
Arg
Ser
Third
mR
NA
base
(3
end
of c
odon
)
64 codons; 20 amino acids
The genetic code is redundant: more than one codon may specify a particular amino acid
UNIVERSAL GENETIC CODEFIGURE 14.7
(a) Tobacco plant expressinga firefly gene
(b) Pig expressing a jellyfishgene
FIGURE 14.10
Nontemplate strand of DNA
Direction of transcription
RNA polymerase
3
53
5
RNA nucleotides
Template strand of DNA
Newly made RNA
3 end
5
UC
U
G
A
A
A
A
AA
A
AA
A
T T T
TTT
T
CC
C
CCC C
G
GG
U
TRANSCRIPTION
RNA polymerase assembles 5’ to 3’
-can start a chain without a primer
FIGURE 14.8-3 Transcription unit
RNA polymerase
Promoter
Template strand of DNA
Start point
Termination
Completed RNA transcript
RNA transcript
UnwoundDNA
RewoundDNA
RNA transcript
Direction oftranscription(“downstream”)
Initiation
Elongation
35
35
35 3
5
35
35
35
35
35
35
3
2
1
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf
PROKARYOTES
EUKARYOTESFIGURE 14.9
Transcription factors
TATA box
Promoter Nontemplate strand
Start point
Transcriptioninitiationcomplex forms.
Transcription initiation complex
DNA
RNA transcript
A eukaryoticpromoter
Several transcriptionfactors bind to DNA.
35
5 3 35
35
35
3
2
1Template
strand
Transcription factors
RNA polymerase II
35
35 TA T A A A A
ATA T T T T
Transcription factors mediate the binding of RNA polymerase and the initiation of transcription
EUKARYOTIC CELLS MODIFY RNA AFTER TRANSCRIPTION
FIGURE 14.UN03
DNA
Pre-mRNA
mRNA
Ribosome
Polypeptide
TRANSLATION
TRANSCRIPTION
RNA PROCESSING
RNA PROCESSING
Protein-coding segmentPolyadenylation
signal
G P
A modified guaninenucleotide added tothe 5 end
50–250 adeninenucleotides added to the 3 end
35
5 Cap 5 UTR 3 UTR Poly-A tailStartcodon
Stopcodon
P P AAUAAA …AAA AAA
Modifications:• The 5 end receives a modified G nucleotide 5 cap• The 3 end gets a poly-A tail
Functions:• Facilitating the export of mRNA to the cytoplasm• Protecting mRNA from hydrolytic enzymes• Helping ribosomes attach to the 5 end
ALTERNATIVE RNA SPLICING
FIGURE 14.12
Introns cut out andexons spliced together
31–104
5 Cap
5 UTR 3 UTR
Poly-A tail
Codingsegment
1–146
AAUAAA
105– 146
5 Cap Poly-A tail1–30
mRNA
Pre-mRNAIntron Intron
RNA splicing removes introns (noncoding) and joins exons (translates to amino acids), creating an mRNA molecule with a continuous coding sequence
TRANSLATION
FIGURE 14.14
5
tRNA
Polypeptide
Ribosome
Anticodon
mRNA
Codons 3
tRNA withamino acidattached
Amino acids
Gly
Trp
Phe
A A A
A C CC
CG
U U U G G CU G G
A cell translates an mRNA message into protein with the help of transfer RNA (tRNA)
TRNAFIGURE 14.15
5
Anticodon
3
Amino acidattachment site
AnticodonAnticodon
A A G53
Hydrogenbonds
53
Amino acidattachment site
Hydrogenbonds
A
A
G
A
CG
CC
C
C
UA
C G
UU
AA A
A
C
G U
A
C G U
A
C
GU
AC
G
U
*
CG
*
G
GU
A
AA
A
C C
C
CC
GGGG
G
UUU
U
GG
G
G
A
A
* *
*
*
*
*
**
*
(b) Three-dimensional structure
(c) Symbol used in this book(a) Two-dimensional structure
*
FIGURE 14.17
PE A
tRNAmolecules
A
Largesubunit
Smallsubunit
Growing polypeptide Exit tunnel
E P
mRNA5 3
Growing polypeptide(a) Computer model of functioning ribosome
tRNA
5
3E
mRNA
(c) Schematic model with mRNA and tRNA
Codons
Amino end Next amino acidto be added to
polypeptidechain
Largesubunit
Smallsubunit
A site (Aminoacyl-tRNA binding site)
P site (Peptidyl-tRNA binding site)
Exit tunnel
E site (Exit site)
mRNA binding site
(b) Schematic model showing binding sites
RIBOSOME STRUCTURE
INITIATIONFIGURE 14.18
A
Small ribosomal subunit bindsto mRNA.
GTP
P siteU A
mRNA5 3
Met
P i
mRNA binding site
Start codonSmallribosomalsubunit
InitiatortRNA
5 3
53
Large ribosomal subunit completes the initiation complex.
U GC
53
Translation initiation complex
Largeribosomalsubunit
AE
Met
GDP
1 2
3 stages:InitiationElongationTermination
http://www.pbslearningmedia.org/asset/lsps07_int_celltrans/
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf
FIGURE 14.19-3 Amino endof polypeptide
mRNARibosome ready fornext aminoacyl tRNA P
site
P i
5
3E
GTP
Asite
GDP
Peptide bondformation
Codon recognition
Translocation
E
P A
E
P A
P i
GTP
GDP
E
P A
32
1
ELONGATION
TERMINATIONFIGURE 14.20-3
Freepolypeptide
Ribosome reaches astop codon on mRNA.
5
3
2 GTP
2 GDP P i
Releasefactor
Stop codon(UAG, UAA, or UGA)
5
35
3
Ribosomalsubunits and othercomponentsdissociate.
Release factorpromoteshydrolysis.
2 31
POLYRIBOSOMES
FIGURE 14.22
Incomingribosomalsubunits
(b) A large polyribosome in a bacterialcell (TEM)
Ribosomes
mRNA
(a) Several ribosomes simultaneously translating onemRNA molecule
0.1 m
Start of mRNA(5 end)
End of mRNA(3 end)
Growingpolypeptides
Completedpolypeptide
Polyribosome
A number of ribosomes can translate a single mRNA molecule simultaneously
REVIEW
FIGURE 14.24
A
U A
tRNA
5 Cap
3
mRNA
Ribosomalsubunits
Aminoacyl(charged)tRNA
PE
G
5
3
Ribosome
Codon
Anticodon
TRANSLATION
Aminoacid
Aminoacyl-tRNAsynthetase
CYTOPLASM
NUCLEUS
AMINO ACIDACTIVATION
Intron
5 Cap
Poly-A
TRANSCRIPTION
RNAPROCESSING
RNAtranscript
RNA transcript(pre-mRNA)
RNApolymerase
Exon
DNA
Poly-A
Poly-A
U GUG U UA A A
A C C UA
CAE
http://www.pbslearningmedia.org/asset/lsps07_int_celltrans/