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BIOL 2317 topic 2
| Question | Answer |
|---|---|
| RNA characteristics | Abundant in all cells, chemically similar to DNA, cell location suggested role for RNA in protein synthesis |
| Protein synthesis happens where | Cytoplasm |
| DNA synthesis happens where | Nucleus |
| What is transcription | Synthesis of a single-stranded RNA using a DNA template |
| Characteristics of transcription | RNA pol adds to the 3', complementary base pairing, anti-parallel |
| Same about RNA and DNA pol | 5' to 3' synthesis, catalyze phosphodiester bond formation |
| Different about RNA from DNA | A adds U, Does not need 3' OH primer, Single strand DNA, No proofread |
| Different about DNA from RNA | A adds T, Needs a primer, double stranded, proofreading exonuclease , replication in nucleus |
| Messenger RNA | Produced from protein-coding genes, short-lived intermediate between DNA and protein, only one that undergoes translation |
| Functional RNA's | Don't encode proteins, perform functional roles in cell |
| What percentage encodes proteins | less than 2% |
| Template strand | Strand that is read by RNA pol to synthesize a complementary strand |
| Coding strand | Same 5' to 3' polarity as RNA transcript and has the same sequence |
| Promoter | Controls RNA pol access to gene, promotes transcription, upstream, beside +1 site, position is important |
| Coding region | Contains info needed to synthesize gene product |
| Termination region | Regulates termination of transcription, regulatory sequence |
| RNA polymerase and bacterial transcription | one catalyzes the transcription |
| RNA polymerase core enzyme | No sigma, multiple subunits, can't bind to a promoter |
| RNA polymerase holoenzyme | Core and sigma, can bind to promoters with sigma subunits |
| Pribnow box | -10 consensus sequence (5' TATAAT 3') |
| Stages of transcription | 1. Initiation 2. Elongation 3. Chain termination |
| Steps of Initiation | 1. Closed complex promoter 2. Open complex promoter |
| Closed complex promoter | DNA remains double stranded, RNA pol holoenzyme binds to the promoter |
| Open complex promoter | DNA is unwound, RNA pol holoenzyme moves to its nucleotide |
| What happens in elongation | No primer is required, RNA pol ads to the 3' end, holoenzyme is intact for 8-10 nucleotides, sigma dissociated, double helix unwinds ahead of RNA pol and reforms behind |
| What happens in termination | Core enzyme dissociates, after 1st round ends, second round begins |
| Termination mechanisms | Intrinsic and Rho-dependent |
| Intrinsic termination | Most common in bacteria, induces structural change for termination, includes inverted repeat followed by repeating adenines (in DNA) |
| Inverted repeat | Sequence is transcribed into RNA, stem loop can form |
| What causes RNA pol to slow down and destabilize in a stem loop | RNA followed by a stretch of U's |
| RHO-dependent termination | Inverted repeat forms stem loop, requires rho, hitchhikes on RNA pol during transcription |
| Modifications to produce mature mRNA include | 1. 5' capping 2. 3' polyadenylation 3. Intron splicing |
| Where do modifications occur | In the nucleus |
| 5' capping | Guanine + methyl group makes the cap, has triphosphate linkage |
| Methyl transferase | enzyme that adds methyl groups to newly added guanine |
| Functions of the 5' cap | 1. Protect mRNA from degradation 2. Facilitate transport of mRNA out of nucleus 3. Facilitate intron splicing 4. Enhance translation efficiency by orienting ribosome on mRNA |
| 3' polyadenylation | 3' end cleaves section and replaces with string of adenines, pre RNA is cut after signal sequence, 3' fragment destroyed, PAP adds A's to new 3', |
| PAP | Polyadenylate polymerase, binds to poly a signal hear 3' end of pre-mRNA |
| PAB | Increase processivity of PAP |
| Functions of polyadenylation | 1. Transport of mature mRNA across nuclear membrane to cytoplasm 2. Protect mRNA from degradation 3. Enhance translation |
| Parts of intron splicing | Introns and exons |
| Introns | Intervening sequences between exons of eukaryotic genes that are NON-CODING |
| Exons | non-intron segment of coding sequence of a gene, join after intron removal, spliced exons encode amino acid sequence |
| Spliceosome | Large protein RNA complex that removes introns and joins exons , forms lariat structure |
| Branc point sequence | Conserved adenine and stretch of pyrimidines |
| Alternative splicing | Splicing of identical pre-mRNA that leads to mature mRNA with different combinations of exons Always need 5' and 3' splice site Always remove all introns and sometimes exons |
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user-2006655