BIOLCHEM 415 1st Edition Lecture 33Outline of Last Lecture I. Transcription is the first step in gene expressionOutline of Current Lecture II. Eukaryotic Cells have three types of RNA polymeraseIII. RNA polymerase II requires complex regulationIV. Gene expression is regulated by hormonesV. Histone acetylation results in chromatin remodelingCurrent LectureGene – produces functional RNA molecule- encodes protein (~2% of RNA)- biochemical functions- “non-coding” RNA Gene regulation in eukaryotic cells- generate different cell types- genes produce specific cells- shared “house-keeping” cells1 – complexity (3 polymerases)2 – RNA processing (specifically mRNA)3 – nuclear membrane- separates RNA synthesis from protein synthesis- transcription of RNA occurs in the nucleus- protein translation occurs in the cytoplasmThese 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.3 RNA polymerases- α-amanitin (death cap mushroom)- affects polymerase II- blocks synthesis of mRNA precursors- similar structure to prokaryotic RNA polymeraseNon-coding RNA- rRNA and tRNA- protein synthesis- nuclear RNA - splicing abilities- gene regulationEukaryotic promoters - each type has a distinct promoter region- cis-acting elements- controlling sequences on same DNA molecule- transcription factors- proteins that regulate gene expressionPolymerase II- transcribe mRNA (~ 25000 protein coding genes)- TATA box + initiator element- initiator + downstream promoter elementPolymerase I- located in nucleolus- rRNA- ribosomal initiator + upstream promoter element- 5 arrays of 300-400 rRNA genesPolymerase III- tRNA and a rRNA- A block + C block for rRNA- A block // B block for tRNA- ~500 tRNA genesActive transcription complexes (polymerase II)- transcription factors bind to promoters- TFII- when TATA box is present then a TATA-box-binding-protein (TBP)- TFIID component Transcription Initiation- TFII(A-F and H) all recruited- polymerase II also binds at this time- TFIIH opens double helix- phosphorylates carboxyl-terminal domain of polymerase- allows to leave promoter and begin tracsription- intiation elongation Enhancers- cis-acting and not promoters- stimulate transcription of promoters- loop DNA with protein-protein interactionsCoactivators and Mediator- transcription factors - coactivators – facilitate transcription by polymerase II - mediator- large complex - bridge between enhancer bound activators and proteins at promoterRegulation of transcription1 – DNA binding regulatory proteins- activators and repressors2 – DNA looping- enhancers in contact with promoters3 – combinatorial controlCell identity- pluripotent stem cells- induced pluripotent stem cells- generated differentiated cells- insertion of genes for only 4 specific transcription factorsHormone regulation- steroid hormones - nuclear hormone receptors- DNA binding domain- response elements- estrogen recruits coactivator- ligand binding creates conformational change and docking site for protein - some cancers dependent on these hormonesHistone remodeling chromatin- packaging can impede transcription - coactivators loosen interaction between histones and DNAHistone acetylation- chromatin remodeling- HATS - modify- coactivator components- acetylation- reduces affinity for DNA- acetyl from acetyl CoA lysine on histone tail- docking site for protein- recruitcoactivator to remodel- recruit polymeraseHistone deacetylase enzymes- removal of acetyl groups from histones- repressed genes in heterochromatin - tightly packed deacetylated
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