Transcripción del ADN

Chapter 10Chapter 10 11

11 22

11 22

Sitio Catalítico

tRNA docking sites

Attached amino acidTransfer RNA

Subunidad ribosomica pequeña

Ribosomecontains rRNA

SubunidadRibosomicagrande

CC

AA

GG

AA

UU

GG

GG

AA

GG

UU

UU

AA

UU

GG

GG

mRNAmRNA

AA GG UU

Met

anticodon

Three Types of RNAThree Types of RNA


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InformaInformation tion

Flow:Flow:DNA=>DNA=>RNA=>RNA=>ProteinProtein


11 22 Transcription:Transcription:First Two StepsFirst Two Steps


11 22 Transcription:Transcription:Last StepLast Step


11 22 RNA Transcription in ActionRNA Transcription in Action


11 22 Translation:Translation:An OverviewAn Overview


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A tRNA with an A tRNA with an attached methionine attached methionine amino acid binds to a amino acid binds to a small ribosomal small ribosomal subunit, forming an subunit, forming an initiation complex. initiation complex.

Translation:Translation:Initiation (1)Initiation (1)


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The initiation The initiation complex binds to complex binds to end of mRNA and end of mRNA and travels down until it travels down until it encounters an AUG encounters an AUG codon in the mRNA. codon in the mRNA.

The anticodon of the The anticodon of the tRNA in the initiation tRNA in the initiation complex forms base complex forms base pairs with the AUG pairs with the AUG codon.codon.



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The large The large ribosomal subunit ribosomal subunit binds to the small binds to the small subunit, with the subunit, with the mRNA between the mRNA between the two subunits.two subunits.

The methionine The methionine tRNA is in the first tRNA is in the first tRNA site on the tRNA site on the large subunit. large subunit.



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The second tRNA enters the The second tRNA enters the second tRNA site on the second tRNA site on the large ribosomal subunit.large ribosomal subunit.

Which tRNA binds depends Which tRNA binds depends on the ability of its anticodon on the ability of its anticodon (CAA in this example) to base (CAA in this example) to base pair with the codon (GUU in pair with the codon (GUU in this example) in the mRNA.this example) in the mRNA.

tRNAs with a CAA anticodon tRNAs with a CAA anticodon carry an attached valine carry an attached valine amino acid, which was added amino acid, which was added to it by enzymes in the to it by enzymes in the cytoplasm.cytoplasm.

Translation:Translation:Elongation 1Elongation 1


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The "empty" tRNA is The "empty" tRNA is released and the ribosome released and the ribosome moves down the mRNA, moves down the mRNA, one codon to the right.one codon to the right.

The tRNA that is attached The tRNA that is attached to the two amino acids is to the two amino acids is now in the first tRNA now in the first tRNA binding site and the binding site and the second tRNA binding site second tRNA binding site is empty.is empty.



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The catalytic site on The catalytic site on the large subunit the large subunit catalyzes the catalyzes the formation of a peptide formation of a peptide bond linking the bond linking the amino acids amino acids methionine to valine.methionine to valine.

The two amino acids The two amino acids are now attached to are now attached to the tRNA in the the tRNA in the second binding second binding position.position.



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Another tRNA enters the Another tRNA enters the second tRNA binding site second tRNA binding site carrying its attached carrying its attached amino acid.amino acid.

The tRNA has an The tRNA has an anticodon that pairs with anticodon that pairs with the codon. (Here, the CAU the codon. (Here, the CAU mRNA codon pairs with a mRNA codon pairs with a GUA tRNA anticodon.)GUA tRNA anticodon.)

The tRNA molecule carries The tRNA molecule carries the amino acid histidine the amino acid histidine (his).(his).



11 22 Translation:Translation:Elongation 5Elongation 5

Binding of tRNAs, & Binding of tRNAs, & formation of peptide formation of peptide bonds continues.bonds continues.

Ribosome reaches Ribosome reaches STOP codon (UAG).STOP codon (UAG).

Protein "release Protein "release factors" signal the factors" signal the ribosome to release ribosome to release the protein.the protein.

The mRNA is also The mRNA is also released and large & released and large & small subunits small subunits separate.separate.


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The catalytic site forms The catalytic site forms a new peptide bond, in a new peptide bond, in this example, between this example, between the valine and the the valine and the histidine.histidine.

A three-amino acid A three-amino acid chain is now attached chain is now attached to the tRNA in the to the tRNA in the second tRNA binding second tRNA binding site.site.

The empty tRNA in the The empty tRNA in the first site is released first site is released and the ribosome and the ribosome moves one codon to moves one codon to the right.the right.

Translation:Translation:TerminationTermination


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GG GG GG AA GG CC GG AA UU UU UU

CC AA AA CC AA UU CC CC UU

Methionine Glycine Valine etc.

GG GG GG AA GG TT TT CC TT GG AA

templateDNA strand

(a) complementaryDNA strand

(b) mRNA

(c) tRNA

(d) protein

amino acids

anticodons

codons

gene

etc.

etc.

etc.

etc.

GG TT CC CC CC CC AA AA AA TT CC

Complementary Base PairingComplementary Base Pairing


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AminoAminoAcidsAcids

ActiveActiveProteinProtein

Overview ofOverview ofInformation FlowInformation Flow

InactiveInactiveProteinProtein

(Cytoplasm)(Cytoplasm)

DNADNA(Nucleus)(Nucleus)

rRNArRNA tRNAtRNA1 TranscriptionTranscription

+ Proteins+ Proteins

RibosomesRibosomestRNAtRNA

tRNA-AAtRNA-AA

mRNAmRNA

mRNAmRNA

2 TranslationTranslation

3 ModificationModification

ProductProductSubstrateSubstrate4 DegradationDegradation

Education

Transcripción del ADN