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Initiating translation

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Presentation on theme: "Initiating translation"— Presentation transcript:

1 Initiating translation
Fig Initiating translation Large ribosomal subunit 3 U 5 A C P site Met 5 A 3 Met U G Initiator tRNA GTP GDP E A mRNA 5 5 3 3 Start codon Small ribosomal subunit mRNA binding site Translation initiation complex

2 GDP GDP Amino end of polypeptide E 3 mRNA Ribosome ready for
Fig Amino end of polypeptide E 3 mRNA Ribosome ready for next aminoacyl tRNA P site A site 5 GTP GDP E E P A P A GDP GTP E P A

3 Terminating translation
Fig Terminating translation Release factor Free polypeptide 5 3 3 3 2 5 5 GTP Stop codon (UAG, UAA, or UGA) 2 GDP

4 Translation animation
How is this model different than what is in your textbook? How are aminoacyl-tRNAs brought to the ribosome? How are hydrogen bonds represented? How is the expenditure of energy (GTP) represented? What is “peptidyl synthetase”?

5 DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide
Fig. 17-3a-2 DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide (a) Bacterial cell

6 Completed RNA transcript
Fig. 17-7a-4 Promoter Transcription unit 5 3 3 5 DNA Start point RNA polymerase 1 Initiation 5 3 3 5 RNA transcript Template strand of DNA Unwound DNA 2 Elongation Rewound DNA 5 3 3 3 5 5 RNA transcript 3 Termination 5 3 3 5 5 3 Completed RNA transcript

7 Translation can happen while transcription is still ocurring
Fig RNA polymerase DNA mRNA In bacteria: Translation can happen while transcription is still ocurring Polyribosome Direction of transcription 0.25 µm RNA polymerase DNA Polyribosome Polypeptide (amino end) Ribosome mRNA (5 end)

8 Polypeptide subunits that make up enzymes for tryptophan synthesis
Fig. 18-3a In bacteria: Many genes are organized in operons Operon = group of genes sharing one promoter, expressed as 1 mRNAs containing multiple ORFs trp operon Promoter Genes of operon trpE trpD trpC trpB trpA Start codon Stop codon mRNA 5 E D C B A Polypeptide subunits that make up enzymes for tryptophan synthesis

9 Nuclear envelope DNA TRANSCRIPTION Pre-mRNA mRNA TRANSLATION Ribosome
Fig. 17-3b-3 Nuclear envelope DNA TRANSCRIPTION Pre-mRNA RNA PROCESSING mRNA TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell

10 Several transcription factors must bind to the DNA before RNA
Fig. 17-8 A eukaryotic promoter includes a TATA box 1 Promoter Template 5 3 3 5 TATA box Start point Template DNA strand 2 Several transcription factors must bind to the DNA before RNA polymerase II can do so. Transcription factors 5 3 3 5 3 Additional transcription factors bind to the DNA along with RNA polymerase II, forming the transcription initiation complex. RNA polymerase II Transcription factors 5 3 3 5 5 RNA transcript Transcription initiation complex

11 Protein-coding segment Polyadenylation signal 5 3
Fig. 17-9 A eukaryotic mRNA Protein-coding segment Polyadenylation signal 5 3 G P P P AAUAAA AAA AAA 5 Cap 5 UTR Start codon Stop codon 3 UTR Poly-A tail

12 Many eukaryotic mRNAs are spliced
Fig Many eukaryotic mRNAs are spliced 5 Exon Intron Exon Intron Exon 3 Pre-mRNA 5 Cap Poly-A tail 1 30 31 104 105 146 Introns cut out and exons spliced together Coding segment mRNA 5 Cap Poly-A tail 1 146 5 UTR 3 UTR

13 RNA transcript (pre-mRNA) 5 Exon 1 Intron Exon 2
Fig RNA transcript (pre-mRNA) 5 Exon 1 Intron Exon 2 Protein Other proteins snRNA snRNPs

14 RNA transcript (pre-mRNA) 5 Exon 1 Intron Exon 2
Fig RNA transcript (pre-mRNA) 5 Exon 1 Intron Exon 2 Protein Other proteins snRNA snRNPs Spliceosome 5

15 RNA transcript (pre-mRNA) 5 Exon 1 Intron Exon 2
Fig RNA transcript (pre-mRNA) 5 Exon 1 Intron Exon 2 Protein Other proteins snRNA snRNPs Spliceosome 5 Spliceosome components Cut-out intron mRNA 5 Exon 1 Exon 2

16 Gene DNA Exon 1 Intron Exon 2 Intron Exon 3 Transcription
Fig Gene DNA Exon 1 Intron Exon 2 Intron Exon 3 Transcription RNA processing Translation Domain 3 Domain 2 Domain 1 Polypeptide


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