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28 Cards in this Set
- Front
- Back
transcription |
-performed by RNA polymerase which is large -primer is NOT required |
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RNA structure |
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classes of RNA |
1. ribosomal RNA (rRNA) 2. messenger RNA (mRNA) 3. transfer RNA (tRNA) 4. small nuclear RNA (snRNA) 5. micro RNA (miRNA) + small interfering RNA (siRNA) 6. ribozymes |
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rRNA |
-make up ribosomes along with ribosomal protein subunits; site of protein assembly |
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mRNA |
-carry coding instructions from DNA --> ribosomes; specifies sequence of amino acids; derived from pre-mRNA after processing |
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tRNA |
-brings amino acid to match the coding triplet in the mRNA to elongate the polypeptide chain; reads language of amino acids and nucleic acids |
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snRNA |
-combine with small nuclear protein subunits to form small ribonucleoproteins (snRNPs) -process pre-mRNA --> mRNA -exon splicing |
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miRNA + siRNA |
-eukaryotic cells -degrade or inhibit further translation of mRNA |
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transcription unit |
-region of DNA that codes for an RNA molecule 1. promoter: determines which strand to transcribe, transcription apparatus recognizes/binds, determines transcription start site (first nucleotide to transcribe into RNA) 2. RNA-coding region: DNA sequence copied into RNA 3. terminator: DNA sequence that signals transcription to end; termination occurs after the terminator sequence has been copied |
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DNA template |
-transcription takes place on only one DNA strand (replication takes place on both) -template strand: DNA transcribed -non-template strand: not transcribed -a gene can only be transcribed from one strand, but all genes don't reside on one strand; both will be used -promoter dictates which one |
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RNA synthesis |
-RNA molecule is formed that is complementary to the template DNA strand -no primer -5' --> 3' -complementary and antiparallel -U instead of T |
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prokaryotic RNA polymerase |
-ALL transcription sets are carried out by RNA pol -large enzyme consisting of several polypeptide chains -core RNA polymerase molecule consists of 5 subunits that catalyze elongation: alpha, alpha, beta, beta', omega -other subunits join and leave the core during transcription 1. sigma factors: control the binding of RNA pol to the promoter 2. rho factors: facilitate transcription termination |
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other subunits of RNA polymerase |
-join and leave the core during transcription 1. sigma factors: control the binding of RNA pol to the promoter 2. rho factors: facilitate transcription termination |
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prokaryotic initiation |
-promoter recognition -sigma subunit of RNA polymerase: binds to promoters -prokaryotic promoters: 1. TATAAT (Pribnow box, 10 bases upstream of the start site) 2. TTGACA (35 bases upstream) -RNA polymerase combines with sigma subunit (holoenzyme) at the +1 site (transcription start site) |
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holoenzyme |
-core protein (RNA poly) + sigma subunit = fully functioning enzyme -combine at +1 (transcription start site) |
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prokaryotic elongation |
-sigma subunit dissociates and RNA polymerase continues elongation -moves downstream -RNA polymerase unwinds the DNA (no helicase like in replication) -topoisomerase: relieves supercoiling ahead and behind the transcription bubble |
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prokaryotic termination |
-occurs due to the transcription unit recognizing a termination sequence -RNA is released from RNA poly -dissociation of RNA and DNA template -two types: 1. rho-dependent termination 2. intrinsic termination |
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rho-dependent termination |
-able to cause termination only in the presence of rho factor protein |
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intrinsic termination |
-able to terminate without rho factor -nothing external involved, only DNA sequences that are transcribed are involved -two components 1. inverted repeats: when transcribed into RNA, forms a hairpin loop (complementary base-pair to each other) 2. six adenine nucleotides |
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eukaryotic vs prokaryotic transcription |
1. multiple RNA polymerases in eukaryotes 2. nucleosome structure: packaging of DNA 3. promoter binding and initiation differs |
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types of eukaryotic RNA polymerases |
-RNA poly I: rRNA (ribosomal) -RNA poly II: pre-mRNA, snoRNAs, snRNAs (small nuclear and small nucleolar) -rRNA poly III: tRNA |
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nucleosome structure |
-due to eukaryotic chromatin structure, chromatin remodeling is needed to access the DNA -acetyltransferase protein adds acetyl groups to amino acid ends of histone proteins -destabilizes the nucleosome structure |
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eukaryotic promoter binding |
-promoter recognition: carried out by accessory proteins that bind to promoter 1. general transcription factors: forms basal transcription apparatus with RNA polymerase (low/base level of transcription) 2. transcriptional activator proteins: bind to specific recognition sequences, communication with environment (responding to exntl stimuli like pathogen, heat, stress), enhancing/boosting transcription level, beyond basal rate |
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RNA poly II promoters |
-close to transcription start site -core promoter: immediately upstream of coding sequence (TATA box -30bp, TFIIB recognition element -35bp) -regulatory promoter: immediately upstream of core promoter (CAAT box, GC box, OCT box) |
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enhancers************************ |
-further away from transcription start site (>2kb)
-sequences that increase rate of transcription -transcriptional activators bind to enhancer -can be upstream or downstream of the coding sequence or inside an intron -can involve DNA loops to bridge physical distance between different transcription factors and RNA poly II |
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eukaryotic initiation************************ |
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eukaryotic elongation |
-same prokaryotic -several nucleotides are linked -RNA polymerase leaves the promoter and transcription factors -moves downstream -5' --> 3' -RNA base pair with DNA template |
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eukaryotic termination |
-RNA poly I (rRNA): uses termination factor like rho in bacteria and is sequence specific -RNA poly III (tRNA): transcribes a terminator sequence similar to intrinsic termination in bacteria -RNA poly II (mRNA): not sequence-specific, pre-mRNA is transcribed past the coding sequence needed; mRNA is cleaved at a specific coding sequence to generate 2 segments of pre-mRNA -trailing segment: enzyme Rat1 attaches to 5' end -exonuclease activity degrades mRNA until it reaches RNA polymerase -beginning segment continues to mRNA-processing |