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UI BIOL 1411 - Gene Expression
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Biol 1411 1st Edition Lecture 24Outline of Last Lecture I. TranscriptionII. Genetic CodeOutline of Current Lecture I. Gene Expressiona. Translationb. Gene RegulationCurrent LectureTranslation- RNA (ribonucleic acid) differs from DNAo Usually a single polynucleotide strando The sugar is riboseo Contains uracil (U) instead of thymine (T)- Transfer RNAo tRNA, the adapter molecule, associates information in mRNA codons with specific amino acidso Three functions of tRNA it binds to an amino acid, and is then charger it associates with mRNA molecules it interacts with ribosomes o The conformation of tRNA results from base pairing within the moleculeo 3’ end is the amino acid attachment site- binds covalentlyo Anticodon: at the midpoint of the tRNA sequence- site of base paring with mRNA. Unique for each species of tRNA. - Aminoacyl-tRNA synthetaseso Activiating enzymes- aminoacyl-tRNA synthetases- charge tRNA with the correct amino acidso Each enzyme is highly specific for one amino acid and its correcsponding tRNA; the process of tRNA charging is called the second genetic codeo The enzymes have 3-part active sites: they bind a specific amino acid, a specific tRNA and ATP- Codon-anticodon wobbleThese 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.o Wobble: specificity for the base at the 3’ end of the codon is not always observedo Wobble allows cells to produce fewer tRNA species, but does NOT create any ambiguity in the genetic code- Ribosomes: the workbench-holds mRNA and charged tRNAs in the correct positions to allow assembly of polypeptide chaino Ribosomes have 2 subunits, large and smallo In eukaryotes, the large subunit has three molecules of ribosomal RNA (rRNA) and 49 different proteins in a precise pattern. The small subunits has one rRNA and 33 proteins. - Stages of Translationo Like transcription, translation also occurs in three steps: Initiation: formation of initial complex- a charged tRNA and small ribosomal subunit, both bound to mRNA- Prokaryotes: rRNA binds to mRNA recognition site “upstream” of start codon- Eukaryotes: small subunit bnds to the 5’ cap on the mRNA and moves until it reaches the start codon  Elongation: charged tRNAs enter A site, large subunits acts as peptidyl transferase- When the first tRNA has released its methionine, it moves to the Esite and dissociates from the ribosome- can then become charged again- Elongation occurs as the steps are repeated, assisted by proteins called elongation factors  Termination: stop codon enter the A site - Translation ends when a stop codon enters the A site- Stop codon binds a protein release factor- allows hydrolysis of bond between polypeptide chain and tRNA on the P site- Polypeptide chain separates from the ribosome- C terminus is the last amino acid added- UTR- untranslated region- Gene Regulationo Gene expression begins at the promoter where transcription is initiatedo In selective gene transcription a decision is made about which genes to activateo Otherwise, constant gene transcription is know as constitutive expressiono Regulatory proteins control expression of other genes; most gene are under the control of multiple regulatory proteinso General purpose genes- needed by all cells but not expressed at all times of cell cycleo Specialty function genes- needed for response to specific environmental changes or for specialized cell (tissue) functions o Regulation of protein levels- regulatory control of transcription is a primary determinant of protein level produced from gene expression in eukaryotes (and prokaryotes) - Two types of regulatory protein activity: repressors and activatorso Negative regulation- binding of a repressor protein to DNA prevents transcriptioninitiation can occur in the absence of the repressor proteino Positive regulation- activator protein binds to DNA and stimulates transcription; transcription initiation low in the absence of the activator


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UI BIOL 1411 - Gene Expression

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