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03. Transcription

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Comparao RNA - DNA

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Types of RNA

messenger RNA (mRNA). This will later be translated into a polypeptide.

ribosomal RNA (rRNA). This will be used in the building of ribosomes:

machinery for synthesizing proteins by translating mRNA.

transfer RNA (tRNA). RNA molecules that carry amino acids to the growing polypeptide.

small nuclear RNA (snRNA). DNA transcription of the genes for mRNA, rRNA, and tRNA

produces large precursor molecules ("primary transcripts") that must be processed withinthe nucleus to produce the functional molecules for export to the cytosol. Some of these

processing steps are mediated by snRNAs.

small nucleolar RNA (snoRNA). These RNAs modify tRNA and rRNA (met, etc)

microRNA (miRNA). These are tiny (~22 nts) RNA molecules that appear to regulate theHalf life or translation efficiency of mRNA molecules.

ncRNA. Bacteria. Small RNAs that regulate translation based on ribosome binding ability

XIST RNA. This inactivates one of the two X chromosomes in female vertebrates.

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RNA has complex secondary structure

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Organizao da informao genica

DNA

RNA

5 3

-20 -10 +1 +10 +20 +30

53

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DNA is transcribed to RNA in different gene with different efficiencies

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E.coli

Iniciao

Elongao

Terminao

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Iniciao da transcripo

..3..5

Promotor Transcripto codificante

-20 -10 +1 +10 +20 +30 +40 +50

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Iniciao da transcripo

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Transcrio (localizao da informao)

5-----TTTACA-------------------TATA----------------AAT--------------33-----AAATGT-------------------ATAT

5AAU--------------3

-------------TTA--------------5

-35 -10 +1

BOX

RNA Pol

..3

..5

..5..3

Promotor Transcripto regio codificante

-20 -10 +1 +10 +20 +30 +40 +50

DNA

RNA

DNA

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Sequencias consenso no promotor

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Eficincia dos promotores e diferente e depende da sequncia

Eficincia representa o nmero de vezes que a RNA Pol inicia a transcrio

A eficincia de ligao depende:

. Em parte do estado de super-enrolamento do DNA

(+) -> menos transcrio

(-) -> mais transcrio

. Factores de ativao o inibio (factores de transativao)

. Nos procariotas depende de qual factor sigma () se liga

. Nos eucariotas depende de diferentes factores de transativao

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Terminao da transcrio

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Promotores tipo Pol II (mRNA)

Enhancer // Promotor TATA ........3......5

+1-200 -30

+5000

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Complexo de pre-iniciao e ativao

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Iniciao requer alteraes estruturais do promotor envolvendoprotenas ativadoras

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Topoisomerases e Gyrases tambm funcionam durante a transcrio

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5 CAP

7metil-Guanosine- 3P

Ajuda os ribossomas a

Ligarem o mRNA

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Processamento do 3 do mRNA

Poly-A-Polymerase

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Organizao do mRNA

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3..5

Promotor Transcrito codificante

-20 -10 +1 +10 +20 +30 +40 +50

5 UTR codificante 3UTR Poly A

Organizao do mRNA

7-Met-G

CAP

AAAAA (200bp)

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mRNA export to the cytoplasm

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Nucleolus - ribossomas

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Construo dos ribossomas