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06.11.2014
1
Gene expression
DNA
rRNA
tRNA
mRNA Protein
TP +1 18S 5,8S 28S
Transcription
Processing (autosplicing)
18S 5,8S 28S
DNA
Pro rRNA 45S
rRNAs
Steps of the 1st class genes expression
Assembling of RNP 40S + 60S
18S + 33 proteins = 40S 28S + 5,8S + 5S + 49 proteins = 60S
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TP
Transcription
Transfer of RNP in cytoplasm
Steps of the 2nd class genes expressionE E E EI I IDNA
Pro mRNA
Processing of mRNAmRNA 7MeGppp AAAAAAAAAAAAA..........
Translation
Processing of protein
7MeGppp AAAAAAAAAAAAA..........
Protein
Transcription
Transfer of tRNA to cytoplam
Steps of the 3rd class gene expression (tRNA)
Processing of tRNA
A
TDNA
B
+1
tRNA
Formation of aminoacyl-tRNAAminoacyl-tRNA
Pro-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)
5’-AUUGCAUGAUUACCAUGUA-3’ RNA
Transcription (RNA-polymerase)
*** 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 DNAa) coding; a) transcribed a) translatedb) regulatory; b) non-transcribed b) non-translatedc) modulator;
II. EnzymesRNA-polymerase I Mg++, Ca++
RNA-polymerase IIRNA-polymerase III 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 genesUBF TF II D (TBP) TF III ASL 1 TF II A TF III C
TF II B TF IIIBTF II F; E; H
b) SPECIFIC for transcribed gene
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+1
tL i ie e eP
Step Responsible factors Product Place in the cell
Transcription RNA-polymerase II + TF II D,A,B ..
Pro-mRNA Nucleus
mRNA processinga) Cappingb) Polyadenylationc) Splicing
Guanine-7-methyltransferaseEndonucleasePoly(A)-polymeraseSpliceosome U1-6
mRNA Nucleus
Transfer of mRNA Transfer proteins RNP N C
Translation mRNAtRNARibosomes
Polypeptide Cytoplasm
Protein processing TransferasesChaperones
Active protein Cytoplasm
Steps of expression of structural genes(2nd class) in eukaryotes
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 direction3’-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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-10-20-30-40 +1 +10 +20 +30
TAFs
TFIID
TFIIA
TFIIB
RNA-polymerase II
TFIIF
TFIIE
Initiation of transcription of 2nd class genes
Termination of transcription
T
Capping
Processing of mRNA in eukaryotesE E E EI I I
Pro mRNA
Polyadenylation
7MeGppp
7MeGppp AAAAAA..
mRNA
7MeGppp AAAAAA..
Splicing
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mRNA capping
* Adding of a methylated
GTP (7MeGTP)
* Enzyme gunanine-7-
methyltransferase
* 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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P O 1 2 3 T5’ 3’
Promoter Operator Terminator
Structural genes
P O 1 2 3 T5’ 3’
Repressor
RNA-polymerase
P O 1 2 3 T5’ 3’
Inductor
Structure of operon (transcription unit in prokariotes)
Initiation of transcription in prokaryotes
Promoter Gene
Minimal
enzyme
Sigma
factor
+1