unit #3 schedule: last class: – sanger sequencing – central dogma overview – mutation today:...
TRANSCRIPT
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
TRANSCRIPTIONDNA
mRNA
TRANSLATIONRibosome
Polypeptide
Fig. 17-3b-3
(b) Eukaryotic cell
TRANSCRIPTION
Nuclearenvelope
DNA
Pre-mRNARNA 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-4Promoter Transcription unit
DNAStart pointRNA polymerase
553
3
Initiation
33
1
RNAtranscript
5 5
UnwoundDNA
Template strandof DNA
2 Elongation
RewoundDNA
5
5 5 3 3 3
RNAtranscript
3 Termination
5
5 5 33
3Completed RNA transcript
RNA Polymerase and Promoter
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Prokaryotes vs. Eukaryotes
Fig. 17-9
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
Nuclearenvelope
DNA
Pre-mRNARNA PROCESSING
mRNA
TRANSLATION Ribosome
Polypeptide
Fig. 17-9
Protein-coding segment Polyadenylation signal3
3 UTR5 UTR
5
5 Cap Start codon Stop codon Poly-A tail
G P PP AAUAAA AAA AAA…
© 2011 Pearson Education, Inc.
Fig. 17-10
Pre-mRNA
mRNA
Codingsegment
Introns cut out andexons spliced together
5 Cap
Exon Intron5
1 30 31 104
Exon Intron
105
Exon
146
3Poly-A tail
Poly-A tail5 Cap
5 UTR 3 UTR1 146
Fig. 17-11-1RNA transcript (pre-mRNA)
Exon 1 Exon 2Intron
ProteinsnRNA
snRNPs
Otherproteins
5
Fig. 17-11-2RNA transcript (pre-mRNA)
Exon 1 Exon 2Intron
ProteinsnRNA
snRNPs
Otherproteins
5
5
Spliceosome
Fig. 17-11-3RNA transcript (pre-mRNA)
Exon 1 Exon 2Intron
ProteinsnRNA
snRNPs
Otherproteins
5
5
Spliceosome
Spliceosomecomponents
Cut-outintronmRNA
Exon 1 Exon 25
Minute Paper:
• We have ~20,000 genes yet we can make ~100,000 different protein products. How is this possible if DNARNAProtein?
Fig. 17-3b-3
(b) Eukaryotic cell
TRANSCRIPTION
Nuclearenvelope
DNA
Pre-mRNARNA 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
Nuclearenvelope
DNA
Pre-mRNARNA PROCESSING
mRNA
TRANSLATION Ribosome
Polypeptide
Fig. 17-3a-2
(a) Bacterial cell
TRANSCRIPTIONDNA
mRNA
TRANSLATIONRibosome
Polypeptide
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Translation
Transfer RNA (tRNA) bridges RNA language and amino acid language
Transfer RNA (tRNA)
• Single-stranded RNAs of about 74 - 95 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. 17.14
“Charging” Transfer RNA
• Aminoacyl tRNA Synthetase
• Specific for particular pairs of amino acids and tRNA
• Requires ATP
Campbell 8e, Fig. 17.15
© 2011 Pearson Education, Inc.
Ribosomes and the Mechanism of Translation
Ribosomes and Translation
Three Stages of Translation
InitiationElongation
Termination
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Elongation
© 2011 Pearson Education, Inc.
Termination
Campbell 8e, Fig. 17.21
Signal Peptides
Coming Up:
Tuesday:- Molecular Sculpting:
- Translation, transcript processing, translation
- StudyNotes 8b is due.