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El Dogma Central de la Biología Molecular describe un proceso de

dos pasos, la transcripción y la traducción , por el cual la información

contenida en los genes se transforma en proteínas.

ADN ARN proteínas

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TRANSCRIPCION

TRADUCCION

DNA

mRNA

Ribosoma

Polipeptido

DNA

Pre-mRNA

celula procariotica

Envoltura

Nuclear 

mRNA

TRADUCCION

TRANSCRIPTION

PROCESAMIENTO RNA

Ribosoma

Polipeptido

Eukaryotic cell

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TRANSCRIPCIONDNA

TRADUCCION

Ribosoma

Polipeptido

mRNA

Celula Procariotica

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LE 17-3-5

TRANSCRIPTION

TRANSLATION

DNA

mRNA

Ribosome

Polypeptide

DNA

Pre-mRNA

Prokaryotic cell

Nuclear 

envelope

mRNA

TRANSLATION

TRANSCRIPTION

RNA PROCESSING

Ribosome

Polypeptide

Eukaryotic cell

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DNA

molecula

Gen 1

Gen 2

Gen 3

DNA cadena

(templada)

3 

TRANSCRIPCION

Codon

mRNA

TRADUCCION

Proteina

Amino acido

3 

5 

5 

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Elongacion No-templadaCadena devDNA

RNA

polimerasa

RNA nucleotidos

3  end3 

5 

5 

Nuevo RNA

Cadena templado

ADN

Direccion de transcripcion

(“downstream”)

Promotor 

5 3 

RNA polimerasa

Punto de iniciacion

DNA

Unidad Transcripcion

3 5 

5 3 

3 5 

Unwound

DNA

RNA

tran-

script

Template strand

of DNA

Iniciacion

Elongacion

Terminacion

5 3 

3 5 

5 3 

3 5 

3 5 

Rewound

DNA

RNA

transcripto

5 

Completo RNA transcript

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LE 17-8

Promoter 

5 3

 

3 5

 

TATA box Start point

Transcription

factors

5 

3 3

 

5 

Several transcriptionfactors

Additional transcription

factors

RNA polymerase II Transcription factors

RNA transcript

5 

3 

3 

5 

5 

Transcription initiation complex

Eukaryotic promoters

Template

DNA strand

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LE 17-11

Exon 15

 

Intron Exon 2

Other proteins

Protein

snRNA

snRNPs

RNA transcript (pre-mRNA)

Spliceosome

5 

Spliceosome

componentsCut-out

intron

mRNA

Exon 1 Exon 2

5 

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Exon 15

 

Intron

Otras proteinas

Proteina

snRNA

snRNPs

RNA transcripto (pre-mRNA)

Spliceosoma

Exon 2

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5 

Spliceosoma

Corte-out

intron

mRNA

Exon 1 Exon 2

5 

componentes

Spliceosoma

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Gen

Transcripcion

Procesamiento RNA

Traduccion

Dominio 2

Dominio 3

Dominio 1

Polipeptido

Exon 1 Intron Exon 2 Intron Exon 3

DNA

LE 17 9

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LE 17-9

5 

Protein-coding segment

5  Start codon Stop codon Poly-A tail

Polyadenylation signal

5  3 Cap UTR UTR

LE 17 10

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LE 17-10

5  Exon Intron Exon Intron Exon 3 

Pre-mRNA

1 30 31 104 105 146

Coding

segment

Introns cut out and

exons spliced together 

1 146

5  Cap

5  Cap

Poly-A tail

Poly-A tail

5  3 UTR UTR

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Codón iniciación Codón StopCodón

Cola

(no traducido)Fragmento lectura

(traducido)

Guía

(no traducido)

LE 17 13

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LE 17-13

Polypeptide

tRNA with

amino acid

attached

Ribosome

tRNA

Anticodon

3 

5 

mRNA

Amino

acids

Codons

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Sitio de union

Amino acido

Puentes

Hydrogeno

3 

5 

estructura dos dimensionesAnticodon

Sitio de union

Amino acido

3 5 

Puentes

Hidrogeno

Anticodon Anticodon

Simbolo usadoEstructura tres dimensiones

3  5 

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Amino acidoAminoacil-tRNA

sintetasa (enzima)

Pirofosfato

Fosfatos

tRNA

AMP

Aminoacil tRNA

(un “activado

amino acido”)

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sitio P (Sitio ligadura

Peptidil-tRNA)

sitio E

(sitio salida)

Sitio ligadura

mRNA

Sitio A (sitio de ligadura

Aminoacyl-tRNA)

Subunidad

mayor 

Subunidad

menor 

Schematic model showing binding sites

E P A

LE 17-5

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LE 17-5

Second mRNA base

   T   h   i  r   d  m   R   N   A   b  a  s  e

   (   3

  e  n   d   )

LE 17-16

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LE 17 16

Amino end

mRNA

5 

3 

Growing polypeptide

Next amino acidto be added topolypeptide chain

tRNA

Schematic model with mRNA and tRNA

Computer model of functioning ribosome

5 

3 

E

Codons

Schematic model showing binding sites

Small

subunit

Large

subunit

A site (Aminoacyl-

tRNA binding site)E site

(Exit site)

E P A

mRNA

binding site

P site (Peptidyl-tRNA

binding site)

Smallsubunit

Large

subunit

Exit tunnelGrowing

polypeptidetRNA

molecules

E P A

mRNA

LE 17-16a

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LE 17 16a

tRNA

molecules

Exit tunnel

Growingpolypeptide

Large

subunit

mRNA 3 

Computer model of functioning ribosome

Small

subunit

5 

E P A

INICIACION

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INICIACION

GTPInitiator tRNA

mRNA

5 

3 

mRNA binding site

Small

ribosomalsubunit

Start codon

P site

5 

3 

Translation initiation complex

E A

Largeribosomal

subunit

GDP

LE 17-16c

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LE 17 16c

Amino end

mRNA

5 

3 

Growing polypeptide

Next amino acid

to be added to

polypeptide chain

tRNA

Codons

Schematic model with mRNA and tRNA

E

ELONGACION

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Ribosome ready for 

next aminoacyl tRNA

mRNA

5 

Amino end

of polypeptide

E

Psite

Asite

3 

2

2 GDP

E

P A

GTP

GTP

GDP

E

P A

E

P A

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TERMINACION

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Release

factor 

Stop codon

(UAG, UAA, or UGA)

5 

3 

5 

3 

5 

Free

polypeptide

3 

When a ribosome reaches a stop

codon on mRNA, the A site of theribosome accepts a protein called

a release factor instead of tRNA.

The release factor hydrolyzes the

bond between the tRNA in theP site and the last amino acid of the

polypeptide chain. The polypeptide

is thus freed from the ribosome.

The two ribosomal subunits

and the other componentsof the assembly dissociate.

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LE 17-20

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Ribosomes

mRNA

This micrograph shows a large polyribosome in a prokaryotic cell (TEM).

An mRNA molecule is generally translated simultaneously

by several ribosomes in clusters called polyribosomes.

Incoming

ribosomal

subunits

Growing

polypeptides

End of mRNA(3  end)

Start of mRNA(5

 

end)

Completed

polypeptides

m0.1

LE 17-20a

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Incoming

ribosomal

subunits

Growing

polypeptides

Completed

polypeptide

Start of 

mRNA

(5  end)

End of 

mRNA(3 

end)

An mRNA molecule is generally translated simultaneously

by several ribosomes in clusters called polyribosomes.

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LE 17-20b

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Ribosomes

mRNA

This micrograph shows a large polyribosome in a prokaryotic cell (TEM).

m0.1

LE 17-21

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Ribosomes

mRNA

Signal

peptide

Signal-

recognition

particle

(SRP)SRP

receptor 

protein

CYTOSOL

ER LUMEN Translocation

complex

Signalpeptide

removed

ER

membrane

Protein

LE 17-22

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RNA polymerase

DNA

Polyribosome

RNA

polymerase

Direction of 

transcription

mRNA

0.25

DNA

Polyribosome

Polypeptide

(amino end)

Ribosome

mRNA (5 

end)

m

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Las bases moleculares de la enfermedad anemia falci forme 

Hemoglobina DNA normal

mRNA

3  5  5 3 

5  3  3 5 

Hemoglobina DNA mutante

mRNA

Hemoglobina normal Sickle-cell hemoglobin

Cualquier cambio en la secuencia de los nucleótidos del ADN se denominaMUTACION

normal

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substitucion par-base

No afecta la secuencia de aminoacidos

U en lugar de C

Missense

A en lugar de G

NonsenseU en lugar de A

Stop

Amino terminal

Proteina

5 

3 

Carboxyl terminal

Stop

Stop

Stop

mRNA

normal

Wild type

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Insercion o perdida de un par -base

Frameshift causing immediate nonsense

Extra U

Missing

Frameshift causing

extensive missense

Insertion or deletion of 3 nucleotides:

no frameshift but extra or missing amino acid

Missing

Stop

Stop

Amino terminal Carboxyl terminal

Stop

Wild type

mRNA

Protein

5 

3 

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TRANSCRIPTION

RNA PROCESSING

RNAtranscript

5 

Exon

NUCLEUS

FORMATION OFINITIATION COMPLEX

CYTOPLASM

3 

DNA

RNApolymerase

RNA transcript(pre-mRNA)

Intron

Aminoacyl-tRNAsynthetase

Aminoacid

tRNA

AMINO ACID ACTIVATION

3 

mRNA

A

P

E Ribosomalsubunits

5 

Growingpolypeptide

E A

Activatedamino acid

Anticodon

TRANSLATION

Codon

Ribosome