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Lecture 15

Lecture 15 - Eukaryotic Structure.docx

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Western University
Biology 1002B
Tom Haffie

Lecture 15: Eukaryotic Structure Lactose Lies  Has nothing to do with lactose  E. Coli don't interact with lactose on a regular basis  Operon – respond to galactoside (not lactose)  LacA – transacetylase (puts acetyl groups onto molecules) o Has no function with lactose Elysia  Vvaucheria is a coenocytic alga o Eukaryotic cell o Tube full or organelles Nucleus of Eukaryotic Cell  Gene structure is more complicated than in organelles  Promoters o Position dependent (have to be in the right place) o Attract protein transcription factors  Protein Coding Genes o Within promoter is TATA box  Sequence of AT  Protein binds (TATA binding protein)  Then all other transcription factors bind  Make it more attractive to polymerase  Polymerase II o Transcribes protein-coding genes  Polymerase I & III o Transcribes non-protein-coding genes General Transcription Factors  Always required to transcribe a gene above a basal rate  Help the transcription apparatus to assemble (including RNA polymerase)  Example: TFIID which contains that sequence that recognizes a TATA box – helps RNA polymerase bind Specific Transcription Factors  Time or tissue dependent proteins  May have domains that activate transcription Enhancer  Could be anywhere on chromosome (do not have to be close promoter)  Proximal control elements o Located close to promoters – help with transcription  Distal control elements o Groups of which are called enhancers may be far away from a gene or even in an intron  Activator o Protein that binds to an enhancer and stimulates transcription of a gene  Silencer o Protein stabilize proteins that are inhibitory Differential Gene Regulation  Results from combinations of activators Posttranscriptional Modifications** in eukaryotes  Eukaryotes cells modify the transcript after transcription  If no cap and tail – no protein  Helps it from being digested and helps it exit the nucleus  Capping & Tailing o 5’ end receives a 5’ cap (of GTP) to protect the transcript from digestion as it leaves the nucleus o 3’ – OH groups face beginning rather than the end of molecule o Poly(A) polymerase - 3’ end gets a poly-A tail (of 200 As)  Splicing o Transcript contains coding regions (exons) and non-coding regions
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