06.11.2014
Gene expression
mRNA
DNA
Protein
rRNA
tRNA
Steps of the 1st class genes expression
DNA
P +1
18S
5,8S
28S
T
Transcription
Pro rRNA 45S
Processing (autosplicing)
18S
5,8S
28S
rRNAs
Assembling of RNP 40S + 60S
18S + 33 proteins = 40S
28S + 5,8S + 5S + 49 proteins = 60S
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06.11.2014
Steps of the 2nd class genes expression
DNA
P
E
I
E
I
E
I
E
T
Transcription
Pro mRNA
Processing of mRNA
mRNA
7MeGppp
..........
AAAAAAAAAAAAA
Transfer of RNP in cytoplasm
Translation
7MeGppp
..........
AAAAAAAAAAAAA
Processing of protein
Protein
Steps of the 3rd class gene expression (tRNA)
+1
T
DNA
A
B
Transcription
Pro-tRNA
Processing of tRNA
tRNA
Transfer of tRNA to cytoplam
Aminoacyl-tRNA
Formation of aminoacyl-tRNA
Transcription represents the molecular
process of copying of genetic material from
DNA by synthesis of RNA molecules
5’-ATTGCATGATTACCATGTA-3’ Coding strand (non-transcribed)
3’-TAACGTACTAATGGTACAT-5’ Template strand (transcribed)
Transcription (RNA-polymerase)
5’-AUUGCAUGAUUACCAUGUA-3’ RNA
*** The principles of transcription:
! Template synthesis
! Complimentary synthesis
! Antiparallel synthesis
! Synthesis in one direction only
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APPARATUS OF TRANSCRIPTION
I.
Sequences of DNA
a) coding;
a) transcribed
b) regulatory;
b) non-transcribed
c) modulator;
II. Enzymes
RNA-polymerase I
RNA-polymerase II
RNA-polymerase III
a) translated
b) non-translated
Mg++, Ca++
Mn++
III. Polymerization units (monomers)
ATP, GTP, CTP, UTP
IV. Transcription factors:
a) GENERAL for a particular class of genes
1st class
2nd class genes
3rd class genes
UBF
TF II D (TBP)
TF III A
SL 1
TF II A
TF III C
TF II B
TF IIIB
TF II F; E; H
b) SPECIFIC for transcribed gene
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+1
P
L
e
i
e
i
e
t
Steps of expression of structural genes
(2nd class) in eukaryotes
Transcription
Step
RNA-polymerase II
+ TF II D,A,B ..
Pro-mRNA
Place in
the cell
Nucleus
mRNA processing
a) Capping
b) Polyadenylation
c) Splicing
Guanine-7methyltransferase
Endonuclease
Poly(A)-polymerase
Spliceosome U1-6
Transfer proteins
mRNA
Nucleus
RNP
N C
mRNA
tRNA
Ribosomes
Transferases
Chaperones
Polypeptide
Cytoplasm
Active protein
Cytoplasm
Transfer of mRNA
Translation
Protein processing
Responsible factors
Product
Transcription of structural genes (2nd class) in eukaryotes
1. Initiation
- Assembling of initiation complex (binding of specific and
general transcription factors; RNA-polymerase)
- Identification of +1 and direction of transcription
- local unwinding of DNA
- identification of template strand
2. Elongation
- RNA-polymerase II reads from DNA information in direction
3’-5’
- Synthesis of RNA in direction 5’- 3’
3. Termination
- Recognition of terminator
- RNA-polymerase stops at terminator site
- Dissociation of complex RNA-polymerase-RNA-DNA
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Initiation of transcription of 2nd class genes
-40
-30
-20
-10
+1
+10
+20
+30
TAFs
RNA-polymerase II
TFIID
TFIIF
TFIIA
TFIIE
TFIIB
Termination of transcription
Processing of mRNA in eukaryotes
E
I
E
I
E
I
E
T
Pro mRNA
Capping
7MeGppp
Polyadenylation
7MeGppp
..
AAAAAA
Splicing
mRNA
7MeGppp
..
AAAAAA
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06.11.2014
mRNA capping
* Adding of a methylated
GTP (7MeGTP)
* Enzyme gunanine-7methyltransferase
* Unusual bond 5’ppp5’
CAP:
! Stabilizes 5’ end of
mRNA
! Represents a site of
recognition of mRNA by
ribosomes
Polyadenylation
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Splicing
Types of mRNA splicing
Electron micro-photography of 1st class genes
transcription in nucleolus
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06.11.2014
Structure of operon (transcription unit in prokariotes)
Promoter
5’
P
Operator
O
Terminator
1
3
T
3’
2
3
T
3’
2
3
T
3’
2
Structural genes
RNA-polymerase
5’
P
O
1
Repressor
5’
P
O
1
Inductor
Initiation of transcription in prokaryotes
Sigma
Minimal
Promoter
factor
+1
Gene
enzyme
8