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25 Cards in this Set
- Front
- Back
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What are the important steps of gene expression ? |
Transcription of DNA sequence to RNA and Translation of RNA into Amino acid sequence of a protein |
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What is a gene? |
relativly short sequence of DNA that provides instruction to form proteins |
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What is the Genetic code ? |
- A 3 letter code coding for 20 Amino acids - degenerative - contains start code and stop code |
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Initiation of Transcription |
- RNA polymerase binds to promotor region - no primer is needed |
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Where is RNA polymerase involved and what are its function ? |
Functions: - Synthesis of RNA - Binding to promoter region - unwinding Involved in: - Inititation - Elongation - Termination |
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Sigma factor |
- responsible for Binding capacity - 1 sec - 30 min initiation frequence - reduces binding stability of Core enzyme to false binding sites - only comparatively short molecules are produced at the beginning |
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Promotor (Bacteria) |
- 12 Bases in Bacteria depending on size of the genome ( smaller if "spaces and linker") - Starting point: [+1] -[-10] TATAAT consensus sequence (unwinding domain) - ----------------16-18 bases-------------------- -[-35] TTAGACA recognition domain - lying upstream at 5´region |
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What happens during Elongation? |
- RNA polymerase recognizes and matches complimentary bases - RNA polymerase bonds the sugar and phosphate of the new RNA strand - mRNA grows |
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Termination |
- starts when termination signal is reached - RNA polymerase seperates - RNA detaches - takes place in nucleus - mRNA forms hairpin-loop like structure - DNA strands re-associate leading to a pause in transcription and the mRNA dissociates |
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Events of Transcription |
[1]. RNA polymerase synthesizes a single strand of RNA against DNA template strand ( antisense strain) adding nucleotides to 3´end [2]. Initiation is regulated by transcription factors, including promoters [3]. 3´end cleaved at AAUAAA, and poly A tail is added |
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Non coding regions |
-e.g. centromers and telomeres (may have specific chromosomal functions) - may have regulatory purposes - non -coding; non functional DNA: called junk DNA - EXON: Coding region - INTRON : non coding region |
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Alternative Splicing |
- different ways in which exons of a gene can be combined , producing different forms of proteins within same gene coding region - important mechanism for regulating gene expression in higher eukaryotes - pre- mRNA |
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Forms of alternative splicing |
- primary isoform - cryptic exon - exon etension (5´or 3´) - exon skipping - exon truncation |
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SUMMARY TRANSCRIPTION |
- GOAL: to send nucleotide message (encoded in DNA) from nucleus to cytoplasm - DNA is copied via complementary base pairing (mRNA)--> RNA polymerase catalyzes - START: RNA polymerase binds promoter sequence (on template) - STOP: RNA polymerase meets termination signal - Only a specific Gene is transcribed not whole genome |
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What are the players of Translation ? |
- mRNA: intermediary messenger - rRNA: site for protein synthesis - tRNA: decoder and monomer carrier |
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How many natural Aminoacids are there ? |
20, they differ in side chains on the alpha carbon |
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What are Ribosomes doing ? |
- mediate protein synthesis - attach to specific mRNA sequences (shine dalgano sequence) with 30s subunit - position of ribosome binding site and the initiation codon define reading frame |
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50s subunit of the ribosome |
RNA (23s+5s) + 31 polypeptides
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30s subunit of the Ribosome |
RNA (16s) + 21 polypeptides |
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Ribosome Structure |
- protein lies around periphery of the subunits and acts to stabilize RNA fold - required for translation and peptide bond formation |
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Translation inititation |
- AUG is recognized by methionyl tRNA --> enters p side - small subunit binds to mRNA molecule - tRNA anticodon binds to start codon - large subunit joins with small subunit and initiator tRNA binds to first binding site - cytoplasm |
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Translation Elongation |
- second mRNA codonbase pairs with anticodon of tRNA that enters the second binding site of the large subunit - catalytic side on the large subunit catalyzes the formation of a peptide bond between aminoacids methionine and (x) - initiator tRNA drops off the ribosome, ribosome moves one codon to the right - tRNA bearing newly formed peptide moves to first binding site, second site is emptied - third tRNA plus basepair moves to second site - peptide bond is forged to form three peptide chain, all remain attached to third tRNA. |
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Translation Termination |
- stop codon is reached, - finished peptide is realeased - and subunits seperate |
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Processing and posttranslational modifications |
- chemical modifications: glycosylation, acylation, phosphorylation, proteolytic cleavage - protein folding - molecular chaperones: structures that assemble different proteins to form e.g. enzymes for storage /secretion and localization on the chromosomes |
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What are the STOP codons ? |
UAA; UAG; UGA |
