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WSU BIOLOGY 107 - Gene Expression 2

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BOLOGY 107 Lecture 29Outline of Last Lecture I. Gene Expressiona. Transcription (cont.)b. RNA Processingc. TranslationOutline of Current Lecture II. Gene Expressiona. Translation (cont.)b. Protein targetingc. PolyribosomesIII. Mutationsa. What they areb. How they ariseCurrent LectureGene Expression1) Translation (cont.)a) tRNAi) Cloverleaf structure when modeled in 2D, “l-shaped” in 3Dii) Anticodon- base pair for codons on mRNAiii) Amino acid attachment site (3’), opposite of anticodonb) Activation i) tRNA syntetase binds tRNA to amino acid match(1) Uses one ATP(2) Specific enzyme for each amino acidc) Ribosome i) Consists of protein and RNA(1) rRNA acts as catalyst, protein holds structure(2) Large subunit and small subunitii) 3 binding sites(1) A-site – aminoacyl, new tRNA enters, binds to mRNA(2) P-site – peptidyl, amino acids are bound to each other, most recent still attached to tRNA(3) E-site – exit, empty tRNA leaves the complexThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.(a) Each site aligns with a codon on the mRNAd) Initiation i) Small subunit of the ribosome attaches to mRNA (1) Eukaryotes- bind at 5’cap, bacteria- specific sequenceii) Small subunit lines up with the start codon, start tRNA (methylanine) binds tothe codoniii) Large subunit attaches with start tRNA in P-site(1) Uses GTPe) Elongation i) Codon recognition(1) Aminoacyl tRNA loaded into A-site(a) Anticodons sampled similar to DNA synthesis(b) Uses GTP for loading factorii) Peptide bond formation(1) A-site acid bonded to P-site peptide chain(a) Transfers polypeptide to A-siteiii) Translocation (1) Complex shifts by one condon(a) Uses one GTP(2) Empty tRNA in E-site, tRNA connected to the polypeptide in P-site, A-site open for tRNA(a) Empty tRNA leaves, new tRNA enters, cycle begins againf) Termination i) Protein release factor (RF) binds to stop codon in A-siteii) Bond connecting peptide to P-site tRNA is hydrolyzed, tRNA releases polypeptideiii) Ribosome dissociates, releases mRNA(1) Uses GTPiv) Protein folds into secondary and tertiary structures as it exits the ribosome top2) Protein targetinga) Signal sequence- targets protein to endomembrane systemi) Specific sequence found in first amino acids of new proteinii) Recognized by signal recognition proteins (SRP)iii) Entire ribosome dragged to rough endoplasmic reticulum(1) Injects protein through ER membrane(2) Signal peptide removed from protein during processing3) Polyribosomes (polysomes)a) Multiple ribosomes translate the same mRNAi) Once one ribosome clears the start codon, another can attach and start processingii) Allows for rapid translationb) Linked transcription and translationi) Bacteria do not have a separation for transcription and translation(1) Multiple RNA polymerases can transcribe the same gene(2) Polysomes attach to each mRNA, start translating(3) Exponential protein synthesisMutations4) What they area) Change in DNA sequenceb) Mutations classified by effect on proteini) Silent- no change(1) Same amino acid is coded for in the new codon as in the oldii) Missense- changes amino acidiii) Nonsense mutation- premature termination(1) New codon codes for a stop rather than an acidiv) Framshift- insertion or deletion of bases(1) Number added or deleted is not divisible by three, changes all subsequent codons, shifts “reading frame”(2) Usually results in premature terminationv) Entire codon shift- insertion or deletion of entire codon(1) Number added or deleted is divisible by three, removes or adds an amino acid(2) Subsequent codons are read the same(3) Can still be detrimental, one amino acid can change the whole proteins shape5) How they arisea) Error in DNA replicationi) UV lightii) Ionizing radiationiii) Chemical mutagens(1) While there are mechanisms to correct these errors, the correction mechanisms can have an errorEnd of Exam


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WSU BIOLOGY 107 - Gene Expression 2

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