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Transcription Individual DNA regions (genes) copied to mRNA

Published byEric Thomas Modified over 8 years ago

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Presentation on theme: "Transcription Individual DNA regions (genes) copied to mRNA"— Presentation transcript:

1 Transcription Individual DNA regions (genes) copied to mRNA
One DNA strand is template Single-stranded RNA produced mRNA template strand template strand template strand template strand

2 Transcription Overview
Un beau jour, je suis allé au marché pour acheter du pain. Il faisait chaud. Alors, j’ai acheté aussi un limonade. Il faisait chaud. 2

3 Transcription overview
What do we call this strand? Transcription overview CTACGAGGAGGTGAAGCGATGCCCCGTAGCCGATAGTAGC GATGCTCCTCCACTTCGCTACGGGGCATCGGCTATCATCG DNA gene transcription CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC mRNA

4 Transcription overview
What enzyme makes RNA? Transcription overview CTACGAGGAGGTGAAGCGATGCCCCGTAGCCGATAGTAGC GATGCTCCTCCACTTCGCTACGGGGCATCGGCTATCATCG DNA template strand transcription CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC mRNA 4

5 Transcription overview
What direction is mRNA made? Transcription overview CTACGAGGAGGTGAAGCGATGCCCCGTAGCCGATAGTAGC GATGCTCCTCCACTTCGCTACGGGGCATCGGCTATCATCG DNA template strand transcription – RNA polymerase CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC mRNA 5

6 Transcription overview
What direction is the template strand read? Transcription overview CTACGAGGAGGTGAAGCGATGCCCCGTAGCCGATAGTAGC GATGCTCCTCCACTTCGCTACGGGGCATCGGCTATCATCG DNA template strand transcription – RNA polymerase CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC 5’ 3’ mRNA 6

7 Transcription overview
Which strand does the mRNA look like? Transcription overview CTACGAGGAGGTGAAGCGATGCCCCGTAGCCGATAGTAGC GATGCTCCTCCACTTCGCTACGGGGCATCGGCTATCATCG DNA 3’ 5’ transcription – RNA polymerase CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC 5’ 3’ mRNA 7

8 Transcription overview
How do we know where to start and stop? Transcription overview CTACGAGGAGGTGAAGCGATGCCCCGTAGCCGATAGTAGC GATGCTCCTCCACTTCGCTACGGGGCATCGGCTATCATCG DNA 3’ 5’ transcription – RNA polymerase CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC 5’ 3’ mRNA 8

9 Transcription overview
How is the RNA actually made? Transcription overview RNA polymerase synthesizes RNA 5′→ 3′ Starts at promoter, ends at terminator “upstream” “downstream” DNA +1 start codon stop codon coding region promoter terminator transcription start codon stop codon mRNA 5′ coding region 3′ 5′ UTR 3′ UTR translation NH3 COOH protein

10 Eukaryotic transcription
3 RNA polymerases: RNA polymerase I – rRNA RNA polymerase II – mRNA RNA polymerase III – tRNA RNA polymerase II from yeast

11 Eukaryotic transcription
RNAP II recognizes: TFIID bound to TATA box (TATAAA) TFIIB bound to TFIID Transcription factors bound to enhancer sequences Transcription factors TFIIB TFIID +1 Sp1 hERRa1 CAAT GATA TATA box Enhancers

12 Eukaryotic transcription
RNAP II recognizes: TFIID bound to TATA box (TATAAA) TFIIB bound to TFIID Transcription factors bound to enhancer sequences +1

13 RNA processing in eukaryotes
DNA promoter exons introns primary transcript (nucleus) 5’ cap AAAAAAAAA 3’ poly - A tail splicing transcription unbroken coding sequence transport to cytoplasm for translation final mRNA

14 5′ cap methylated guanine “backward” 5′ to 5′ linkage
Not encoded in DNA Capping enzyme Recognition by ribosome 5′ AGACCUGACCAUACC

15 RNA processing in eukaryotes
DNA promoter exons introns primary transcript (nucleus) 5’ cap AAAAAAAAA 3’ poly - A tail splicing transcription unbroken coding sequence transport to cytoplasm for translation final mRNA

16 3′ poly(A) tail Poly(A) polymerase Add ~200 A’s Not in template
mRNA stability …UGGCAGACCUGACCA 3′ …UGGCAGACCUGACCAAAAAAAAAAAAAAAAAAAA

17 RNA processing in eukaryotes
DNA promoter exons introns primary transcript (nucleus) 5’ cap AAAAAAAAA 3’ poly - A tail splicing transcription unbroken coding sequence transport to cytoplasm for translation final mRNA

18 Splicing Most genes interrupted by introns
Introns removed after transcription Exons spliced together 5’ cap AAAAAAAAA 3’ poly - A tail splicing splicing AAAAAAAAA final mRNA unbroken coding sequence

19 Splicing snRNPs recognize exon-intron boundaries RNA + protein
Cut and rejoin mRNA

20 Splicing RPE65 mRNA in nucleus: 21,000 nt (14 exons) AAAAAAAAA
mature RPE65 mRNA in nucleus: 1,700 nt (8%)

21 Splicing Alternative splicing: >1 protein from one gene
27,000 human genes, but >100,000 proteins

22 Splicing Mutations affecting splicing can cause genetic disease:
cystic fibrosis retinitis pigmentosa spinal muscular atrophy Prader-Willi syndrome Huntington disease spinocerebellar ataxia myotonic dystrophy Fragile-X syndrome Or produce genetic susceptibility to disease: lupus bipolar disorder schizophrenia myocardial infarction type I diabetes asthma cardiac hypertrophy multiple sclerosis autoimmune diseases elevated cholesterol

23 Gene expression summary
Prokaryotes Eukaryotes DNA DNA transcription transcription mRNA pre-mRNA cytoplasm nucleus capping polyadenylation splicing directly translated (even before being completely transcribed) protein mature mRNA transport to cytoplasm translation cytoplasm protein

24 Ribosome Large ribonucleoprotein structure
E. coli: 3 rRNAs, 52 proteins Two subunits: large and small large subunit RNA small subunit protein

25 Eukaryotic Translation
How does the ribosome find the correct start codon? Small ribosome subunit binds 5′ cap Scans to first AUG start codon stop codon cap mRNA 5′ coding region AAAAAAAAA… 3′ 5′ UTR 3′ UTR

26 the Genetic Code After finding start codon, use the genetic code:
Shown as mRNA 5′ → 3′ 26

27 Mechanics of Translation
Translation requires: mature mRNA ribosome tRNAs amino acids accessory proteins

28 tRNA Small RNAs (74-95 nt) made by transcription
Intramolecular base pairing Anticodon complementary to mRNA codon anticodon

29 tRNA “Charged” by specific aminoacyl tRNA synthetase

30 Initiation of Translation
Small ribosome subunit binds at start codon Prokaryotes: Shine-Dalgarno sequence (RBS) Eukaryotes: binds cap, scans mRNA 5′ AUG GAU GGG

31 Initiation of Translation
First tRNA (Met, anticodon CAU) joins complex 5' 3' Met UAC mRNA 5′ AUG GAU GGG

32 Initiation of Translation
Large ribosomal subunit joins 5' 3' Met UAC mRNA 5′ AUG GAU GGG

33 Initiation of Translation
P site holds tRNA with first aa A site open for next tRNA P A 5' 3' Met UAC mRNA 5′ AUG GAU GGG

34 Initiation of Translation

35 Elongation Next tRNA enters CUA P A UAC mRNA 5′ AUG GAU GGG Asp 3' 5'
Met UAC mRNA 5′ AUG GAU GGG

36 Elongation Peptidyl transferase forms peptide bond
Amino acid released from tRNA in P site Met Met Asp mRNA 5′ UAC 3' 5' CUA 3' 5' AUG GAU GGG

37 Elongation Ribosome translocates one codon
First tRNA binds briefly in E site until translocation completes Met Asp 5' 3' UAC mRNA 5′ CUA 3' 5' AUG GAU GGG

38 Elongation Process repeats Next tRNA can then enter the empty A site
5' 3' Gly CCC Met Asp P A mRNA 5′ CUA 3' 5' AUG GAU GGG

39 Elongation

40 Termination Ribosome stops at stop codon No matching tRNA
Release factor binds Met Val Leu Asp Gly Phe Val Lys Gly Leu Gln P A Asp Ile RF GUC 3' 5' UUG CAG UAG

41 Termination Translation complex dissociates UUG CAG UAG GUC RF Met Val
Leu Asp Gly Phe Val Lys Gly Asp Leu Gln Ile UUG CAG UAG 5' 3' GUC RF

42 Polyribosomes Next ribosome starts as soon as start codon is available
Growing polypeptide N RNA subunits released Ribosome 3' 5' AUG mRNA Stop 5' – 3' direction of ribosome movement C N Released polypeptide

43 Protein Synthesis Pathways
Free ribosomes Ribosomes bound to RER

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