Unit #3 Schedule: Last Class: – Sanger Sequencing – Central Dogma Overview – Mutation Today: – Homework 5 – StudyNotes 8a Due – Transcription, RNA Processing, Translation Central Dogma Sculpting (Apr 2) – StudyNotes 8b Due Regulation of Gene Expression + Trivia (Apr 4) – StudyNotes 9 Due Tutorial (Apr 5) Review (Apr 9) – Homework 6 Due EXAM 3 (Apr 11)

Unpacking Central Dogma: Transcription

Learning Objectives: By the end of today’s class you should be able to: 1.Describe transcription. 2.Compare and contrast eukaryotic + prokaryotic transcription. 3.Explain mRNA processing in eukaryotes. 4.Describe the general structure of a tRNA molecule. 5.Discuss the three stages of translation.

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

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

Synthesis of an RNA Transcript The three stages of transcription: – Initiation – Elongation – Termination Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

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

RNA Polymerase and Promoter

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Prokaryotes vs. Eukaryotes

Fig Transcription Termination in Eukaryotes: Transcribes the sequence AAUAAA Signals for the RNA transcript to be cleaved.

Transcription Termination Sequences In Prokaryotes, transcription stops by way of as transcribed terminator. This is part of the transcription sequence that signals RNA polymerase to detach. (Hairpin theory) In Eukaryotes, transcription stops when a polyadenylation signal AAUAAA occurs. Proteins then cleave the RNA transcript off.

Transcript Processing

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

Fig Protein-coding segment Polyadenylation signal 3 3 UTR5 UTR 5 5 Cap Start codon Stop codon Poly-A tail G PPPAAUAAA AAA …

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Fig Pre-mRNA mRNA Coding segment Introns cut out and exons spliced together 5 Cap Exon Intron ExonIntron 105 Exon Poly-A tail 5 Cap 5 UTR3 UTR 1 146

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

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

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

Minute Paper: We have ~20,000 genes yet we can make ~100,000 different protein products. How is this possible if DNA  RNA  Protein?

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

Alternative Splicing Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during RNA splicing. Such variations are called alternative RNA splicing. Because of alternative splicing, the number of different proteins an organism can produce is much greater than its number of genes. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Translation

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

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

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Translation

Transfer RNA (tRNA) bridges RNA language and amino acid language

Transfer RNA (tRNA) Single-stranded RNAs of about nucleotides – On one “end”, they hold an amino acid – On the other “end”, they bind to mRNA There are about 45 different tRNAs in eukaryotic cells

tRNA Structure Campbell 8e, Fig

“Charging” Transfer RNA Aminoacyl tRNA Synthetase Specific for particular pairs of amino acids and tRNA Requires ATP Campbell 8e, Fig

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Ribosomes and the Mechanism of Translation

Ribosomes and Translation Three Stages of Translation Initiation Elongation Termination

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Elongation

© 2011 Pearson Education, Inc. Termination

Campbell 8e, Fig Signal Peptides

Coming Up: Tuesday: -Molecular Sculpting: -Translation, transcript processing, translation -StudyNotes 8b is due.