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Gene Structure & Function Expression.docx

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Western University
Biology 1002B
Tom Haffie

mRNA Gene Structure & Expression  Lots proteins of ETS & Calvin Cycle are coded by genes that are no longer in chloroplasts  Chloroplasts genome is expressed in a prokaryotic environment o Organelle DNA is circular o Some genes on circular genome are transcribed and translated inside chloroplasts tRNA  Elysia o Nuclear genome o Chloroplast genome o Mitochondrion genome  All life is similar Ribosomal RNA  mRNA o Great deal of secondary structure that contains information – its not a ribbon o Can pair with itself – gives it secondary & tertiary structure o Structure and sequence both contain information o Riboswitch (secondary structure) can influence translation Complimentary Base Pairing  Transcription  mRNA & rRNA (SD Box)  mRNA & mRNA  tRNA & tRNA  Ribosomal RNA (orange) base pairs with itself  Enzymatic activity lies in the RNA of ribosomes  Protein o Product of gene expression o Ex. DNA polymerase  Gene codes for more than protein o Ex. RNA – no translation Transcription Initiation  Site of polymerase attachment called promoter  Polymerase read template from 3’ to 5’  Transcription factors help eukaryotic RNA polymerase recognize promoter sequences  RNA polymerase binds to TATA box  DNA strands unwind  Polymerase initiates RNA synthesis at start point Elongation  Template strand = DNA that codes for mRNA  Coding strand = Other strand  Polymerase moves downstream, unwinding DNA and elongating transcript 5  3   No primer required  Continues to untwist double helix, exposing about 10 to 20 DNA bases at a time for pairing with RNA nucleotides  In wake of transcription, DNA strands re-form double helix Termination  Prokaryotes o Polymerase goes right through terminator sequence o After terminator sequence – 5-12 As puts 5-12 Us in mRNA o Terminator sequence pair with itself – complimentary base pair  Makes hairpin loop - secondary structure  Makes polymerase fall of strand o Transcript comes off of DNA Which strand will be the template?  Genes are coded 3’  5’  Genes are coded on either strand  Don't know where promoter is  don't know which strand will be transcribed  Each individual gene has its own template strand – no overall template strand for the entire genome  Posttranscriptional modifications** in eukaryotes o Eukaryotes cells modify the transcript after transcription o If no cap and tail – no protein o Helps it from being digested and helps it exit the nucleus o Capping & Tailing  5’ end receives a 5’ cap (of GTP) to protect the transcript from digestion as it leaves the nucleus  3’ – OH groups face beginning rather than the end of molecule  Poly(A) polymerase - 3’ end gets a poly-A tail (of 200 As) o Splicing  Transcript contains coding regions (exons) and non-coding regions (introns)  Before transcript leaves nucleus, introns must be removed to
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