2B Flashcards
Brief overview of transcription
- Initiation
2.Élongation - Termination
What is an organisms phenotype dependent on
-cell number
-cell type
-cell fxn
Do cells have identical genome
Yes.. difference in expression (transcription)
Gene component
Promoter+transcriptional unit
Promoter in gene?
DNA sequence (include TATA box)-> where transcription begins on chromosome
Where is promoter on gene???
Upstream/5’ of transcriptionalstart point of nontemplate/coding DNA
Transcriptional machinery role
Recognize and bind to promoter to initiate transcription
Transcriptional machinery??
(RNA poly and transcription factors)
Transcriptional unit??
Part of gene copied into RNA (RNA coding region)
Where is the first ribonucleotide added in transcription
Transcription start site
Where is last ribonucleotide added in transcription
Transcription termination site
RNA poly use
-synthesize RNA transcript in 5’->3’ sense (add to 3’-OH.. read DNA template in 3->5)
-NO primer needed to initiate (can initiate from scratch)
-unwind and rewind DNA helix during RNA synthesis
3 types of RNA poly
- RNA Pol I: rRNA
- RNA Pol II: mRNA
- RNA Pol III: tRNA
RNA pol I use
.rRNA-> transcription of noncoding gene (rRNA)
RNA Pol II
Transcription of coding RNA (mRNA)
RNA pol III
.tRNA… transcription of non coding RNA (tRNA)
Step 1: transcriptional initiation
-mediated by DNA binding protein… specific regulatory sequence of gene (RDS)
2 types:
1. General transcription factor bind to promoter=> recruit RNA poly II in low basal level transcription
2. Transcriptional activator protein bind to enhancer region (far from promoter= DNA looping brings mediator and RNA poly to promoter=high level transcription)
Step 2: transcriptional elongation
-RNA poly moves along template DNA (3->5)
-DNA unwound in front of moving RNA poly and reannealing behind transcription Bubble
-ribonucleotide added to 3’ end of RNA transcript (synthesis in 5’->3’)
-growing RNA transcript displaced from DNA template allows reannealing back into dsDNA
Step 3: transcriptional termination
-5’ sequence in DNA template=> termination after transcribed into RNA
- Rho-independent termination (rhohelicase)-> prokaryotes: terminator sequence in mRNA pairs with itself= G-C hairpin= RNA poly dissociate
- Rho-dependent termination (rho helicase)-> prokaryotes: terminator sequence in mRNA is recognized and bound by rhohelicase=> unwind RNA from template DNA and RNA poly
- Cleavage and polyadenylation specific factor (eukaryotes): poly-A-sequence in mRNA signals CPSF cleave completed mRNA transcript= separate fromRNA poly
DNA molecule ds or as
Ds
RNA molecule ds or ss
Ss
WHERE does DNA replication occur
Entire genome
Where does transcription occur
Select location in genome (aka gene)
How many replications per cycle for DNA replication
Replicate genome once/cell cycle
How many RNA synthesized. In transcription
Many RNA in many copies and copies vary through genome
DNA poly need or no need primer
Need cannot synthesize from scratch
RNA poly need primer or not
No, can synthesize de novo
DNA replication end product??
Daughter strand base paired wth parental template strand (semi conservative replication)
Transcription end products
RNA product is detached and ss (NOT remain base paired to template DNA)
Synthesis of new DNA in what direction
DNA replication in 5->3
Synthesis of RNA in what direction
5->3 (transcription)
Postranscriptional regulation of gene expression brief overview
Process mRNA for stability and proper translation
1.5’capping
2. 3’ polyadenylation
3. Splicing
Are the ends of prokaryotic and eukaryotic mRNA translated
NOO….5’ and 3’ are untranslated region
-UTR regulate mRNA stability and translationalefficiency
What does 5’-UTR have
Ribosome binding site (RBS)
-shine dalgarno sequence in prokaryotes
-Kodak box sequence in eukaryotes… fxn in translationalinitiation
ORF
Open reading frame
Region of mRNA translated and includes start and stop codons at borders
Going from DNA to polypeptide what is cut
DNA: promoter+ transcriptionalunit
DNA->mRNA
.mRNA: 5’UTR+ORF+ 3’UTR
RNA->polypeptide
Polypeptide: N-amino acid-C
Postranscriptionalmods of eukaryotic pre-mRNA
Pre-mRNA has processing in nucleus= mature translatable mRNA
- 5’cap- moded Guanosine triphosphate added to5’end of mRNA and act as ribosomebinding site and protect mRNA from degradation
- Poly (A) tail: string of adenine nucleotides added to 3’ end of mRNA by poly-A-polymerase(protect mRNA from degradation and increase translational efficiency
3.introns are removed/spliced during pre-mRNA processing= translatable mRNA
Posttranscriptional processing from pre-mRNA to mRNA
Pre-mRNA has coding segments and UTR (exon) and non coding segment (intron)
Remove intron by splicing-> ORF (codon and UTR)
.mRNA exported from nucleus intro cytoplasm (associate with ribosome)
.mMRNA splicing
Remove intron from pre-mRNA and joining exons=>mature mRNA
Non coding segment (intron) spliced from pre-mRNA.=> UTR+ exons (codon) left in mature mRNA
Splicing by spliceosome (made of 5 noncoding RNA (snRNA)… several proteins (snRNPs… small ribonucleoprotein)
- Bind to intron-exon junction
2.loop intron out of pre-mRNA and bring exon closer - Clip intron at exon boundary
4.join exons
Alternative splicing
Generate diff proteins from 1 gene
Splicing in diff combos= 2+ diff mRNA from gene= severalrelated protein products (isoforms)
-diff isoforms made in diff tissues from same genes producing tissue specific genotype
-increase # and variety of proteins encoded by genome
Posttranscriptional regulation by RNA interference
- microRNA transcribed by RNA Pol II, siRNA (small interfering RNA) also transcribed
- miRNA/siRNA precursor cleaved to ds RNA (substrate of RISC-RNA induced silencing complex) by dicer RNAse
- RISC unwind 1 RNA strand which attracts binding of complementary mRNA
- Binding of mRNA to RISC interferes with translation initiation/induces mRNA degradation (repress gene expression)
Transcriptional regulation
Control of mRNA synthesis
Transcriptional rate depend on speed of transcriptionalinitiation (promoter strength)
Postranscriptional regulation
Process mRNA (affect stability and translational efficiency)
Stability of mRNA depend on presence of 5’CAP and length of poly-A-tail
What does the expression level of a gene depend on
-abundance of mRNA
-nucleotide sequence
-translation
What does abundance of RNA depend on
-rate of synthesis (transcription)
-degradation ofmRNA (Postranscription)
DNA transcriptionalregulation
-chromatin remodeling=> accessible for transcription
-regulatory event at gene promoter and regulatory sequence
DNA postranscriptional regulation
-variation in pre-mRNA processing
-removal of masking protein
-variation in rate of mRNA breakdown
-RNA interference
RNA translationalregulation
Variation in rate of initiation of protein synthesis
RNA post translationalregulation
-variation in rate of protein processing
-removal of masking segments
-variation in rate of protein breakdown
