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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