transcription ahmp 5406. objectives: 1. describe the general process of dna transcription 2. discuss...
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TranscriptionTranscription
AHMP 5406AHMP 5406
Objectives:Objectives:1.1. Describe the general process of DNA transcriptionDescribe the general process of DNA transcription
2.2. Discuss the function of RNA polymerasesDiscuss the function of RNA polymerases
3.3. Differentiate between messenger RNA, small nuclear RNA, ribosomal Differentiate between messenger RNA, small nuclear RNA, ribosomal RNA, and transfer RNARNA, and transfer RNA
4.4. Explain the purpose of the promoter and terminatorExplain the purpose of the promoter and terminator
5.5. Compare and contrast the three types of RNA polymerase in Compare and contrast the three types of RNA polymerase in eukaryotic nuclei: RNA polymerase I, RNA polymerase II, and RNA eukaryotic nuclei: RNA polymerase I, RNA polymerase II, and RNA polymerase IIIpolymerase III
6.6. Discuss RNA capping & RNA splicingDiscuss RNA capping & RNA splicing
7.7. Explain the selective exportation of mRNAs from the nucleusExplain the selective exportation of mRNAs from the nucleus
8.8. Discuss ribosomal RNA and its functionDiscuss ribosomal RNA and its function
What is What is Transcription Transcription ??
DNA does not direct protein DNA does not direct protein synthesis directlysynthesis directly
RNA is used as RNA is used as intermediateintermediate
Transcription = Copying Transcription = Copying DNA into RNADNA into RNA
RNARNA Ribonucleic AcidsRibonucleic Acids
Contain ribose instead of Contain ribose instead of deoxyribose (DNA)deoxyribose (DNA)
Polymers formed by A, G, C, and Polymers formed by A, G, C, and UU
U = uracilU = uracil Complementary to ThymineComplementary to Thymine But sometimes binds to GBut sometimes binds to G
Single strandedSingle stranded Can bind to itself and form 3D Can bind to itself and form 3D
structuresstructures
DNA to RNADNA to RNA
Transcribed RNA is Transcribed RNA is complementary to 1 DNA complementary to 1 DNA strandstrand
Transcribe RNA = Transcribe RNA = transcripttranscript
Transcripts can only reach Transcripts can only reach a few thousand bases in a few thousand bases in lengthlength
UnidirectionalUnidirectional 5’-3’5’-3’
RNA TypesRNA Types
CodingCoding Messenger RNA (mRNA)Messenger RNA (mRNA)
Non-codingNon-coding Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)
Transfer RNA (tRNA)Transfer RNA (tRNA)
Small nuclear RNA (snRNA)Small nuclear RNA (snRNA)
Small nucleolar RNA (snoRNA)Small nucleolar RNA (snoRNA)
mRNAmRNA
Codes for proteinsCodes for proteins
Can be modified by splicing, 5’ and 3’ Can be modified by splicing, 5’ and 3’ additionsadditions
Non-Coding RNAsNon-Coding RNAs
rRNA rRNA Form basic structure of ribosomeForm basic structure of ribosome
tRNAtRNA Adaptors b/w mRNA and AAAdaptors b/w mRNA and AA
snRNAsnRNA Several nuclear processesSeveral nuclear processes Assist in splicingAssist in splicing
snoRNAsnoRNA Process and chemically modify rRNAProcess and chemically modify rRNA
DNA sequences used as signalsDNA sequences used as signals
Sequences signal Sequences signal transcription to start and transcription to start and stop stop
Promoters – start signalsPromoters – start signals factor binds to promoter factor binds to promoter
in bacteriain bacteria
Terminators – stop Terminators – stop signalssignals In bacteria A-T region In bacteria A-T region
causes foldcauses fold
RNA polymerasesRNA polymerases
RNA pols perform transcriptionRNA pols perform transcription
Immediate release of transcript allows Immediate release of transcript allows many RNA to be synth. in a short timemany RNA to be synth. in a short time
More error prone than DNA polsMore error prone than DNA pols
They have limited error correction abilitiesThey have limited error correction abilities
Types of RNA polymerasesTypes of RNA polymerases
RNA pol IRNA pol I Transcribe 5.8S, 18S and 28S genesTranscribe 5.8S, 18S and 28S genes S = Svedberg units, sedimentation coefficient related S = Svedberg units, sedimentation coefficient related
to centrifugationto centrifugation The bigger the number the bigger the moleculeThe bigger the number the bigger the molecule
RNA pol IIRNA pol II Transcribe protein-coding genes, snoRNA genesTranscribe protein-coding genes, snoRNA genes Some snRNA genesSome snRNA genes
RNA pol IIIRNA pol III Transcribe tRNA genes and some snRNA genesTranscribe tRNA genes and some snRNA genes
Transcription in Euks.Transcription in Euks.
Requires general transcription Requires general transcription factors to initiate transcriptionfactors to initiate transcription
GTFs help position RNA pol II GTFs help position RNA pol II correctlycorrectly
TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIHTFIIH
Recognize specific sites on DNARecognize specific sites on DNA
RNA pol start pointsRNA pol start points
TATA Box promoterTATA Box promoter Recognized by subunit of TFIIDRecognized by subunit of TFIID TBP – TATA Box Binding proteinTBP – TATA Box Binding protein approx 25 bp upstream of initiation pointapprox 25 bp upstream of initiation point Causes conformational change in DNACauses conformational change in DNA
Other necessary proteins for Other necessary proteins for initiation of transcriptioninitiation of transcription
Transcriptional activatorsTranscriptional activators Attract RNA pol II to start Attract RNA pol II to start
sitesite
MediatorsMediators Allow communication Allow communication
between activator and between activator and GTFsGTFs
Chromatin remodeling Chromatin remodeling proteinsproteins
Modify DNA conformationModify DNA conformation
Elongation FactorsElongation Factors
Increase affinity of RNA Pol II to DNAIncrease affinity of RNA Pol II to DNA
Assist in moving through chromatin Assist in moving through chromatin structurestructure
mRNA modificationsmRNA modifications
5’ capping5’ capping
Splicing = removing Splicing = removing intronsintrons
3’ Polyadenylation3’ Polyadenylation
5’ Capping5’ Capping
When RNA Pol II at 25 bases When RNA Pol II at 25 bases 5’ cap is added to transcript5’ cap is added to transcript
Modified guanineModified guanine
Three enzymesThree enzymes Phosphatase = removes Phosphatase = removes
phosphate from 5’ endphosphate from 5’ end Guanyl transferase = adds GMPGuanyl transferase = adds GMP
Reversed linkage 5’-5’Reversed linkage 5’-5’ Methyltransferase = adds methyl Methyltransferase = adds methyl
group to guanosinegroup to guanosine
SplicingSplicing
Removes introns (or Removes introns (or sometimes shuffling)sometimes shuffling)
Sequences signal where to Sequences signal where to cutcut
Spliceosome performs Spliceosome performs cuttingcutting Complex of snRNAs (Us) and Complex of snRNAs (Us) and
proteinprotein
Self Splicing MechanismsSelf Splicing Mechanisms
Group IGroup I Bind free G nucleotide to Bind free G nucleotide to
specific sitespecific site
Group IIGroup II Uses reactive A nucleotideUses reactive A nucleotide
Unusual mechanismsUnusual mechanisms
Poly A tailPoly A tail
Cleavage stimulating factor F Cleavage stimulating factor F (CstF)(CstF)
Cleavage and polyadenylation Cleavage and polyadenylation specificity factor (CPSF)specificity factor (CPSF)
Export of mRNAExport of mRNAGoes through nuclear pore complexesGoes through nuclear pore complexes
Mature mRNA are modified and protein boundMature mRNA are modified and protein bound
Signal (passport) for transport of mRNA outside Signal (passport) for transport of mRNA outside of nucleusof nucleus
5’ cap proceeds first5’ cap proceeds first
rRNAsrRNAs
Transcribed by RNA Pol ITranscribed by RNA Pol I
rRNAs are made from a rRNAs are made from a larger precursorlarger precursor Sections are modified, Sections are modified,
cleaved and assembled into cleaved and assembled into ribosomes in nucleolusribosomes in nucleolus
Subnuclear structuresSubnuclear structures
Sites where snRNA Sites where snRNA processing machinery is processing machinery is assembled, stored and assembled, stored and recycledrecycled Cajal bodies Cajal bodies GEMS (Gemini of coiled-GEMS (Gemini of coiled-
bodies)bodies) Interchromatin granule Interchromatin granule
structuresstructures
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