The Eukaryotic Genome - Lecture Slides | BIOL 1107, Study notes of Biology

Download The Eukaryotic Genome - Lecture Slides | BIOL 1107 and more Study notes Biology in PDF only on Docsity! THE EUKARYOTIC GENOME Chapter 14 A. Key Differences Between Eukaryotic & Prokaryotic Genomes ee A Comparison of Prokaryotic and Eukaryotic Genes and Genomes CHARACTERISTIC PROKARYOTES EUKARYOTES , Genome size (base pairs) 10-10’ / 108-10" (Ga Repeated sequences Few 4 . Many Y ; Noncoding DNA within coding Rare fs Common % sequences Wa / ¥ ~ Transcription and translation No ™ Yes separated in cell DNA segregated within a nucleus No Yes DNA bound to proteins Some Extensive Promoters Yes Yes Enhancers/silencers Rare Common Capping and tailing of mRNA No Yes RNA splicing required Rare Common (spliceosomes) Number of chromosomes in One Many genome  [ Transcription ¥ 1. Su INTENT i Transcription Pre-mRNA completed EPRETENTTEETETTTEOOTERTIENEETTENTOEPOETEST COTO mRNA J Processing ‘EEE Translation »sRibosome Polypeptide = Promoter / Pre-mRNA 95’ Start Splice sites codon Stop codon Terminator eExont | Exon2 Intron 1 NA T 3 EB The exons and introns of the coding region are transcribed. 3 23 The introns are removed. EQ The spliced exons are ready for translation after processing. C. Eukaryotic Pre-mRNA Processing Occurs before leaving the nucleus. 1. Capping - a G cap is added to 5’ end; facilitates binding of ribosome & protects mRNA from being digested by ribonucleases 2. Tailing – a poly A tail is added to 3’ end; stabilizes mRNA molecule & assists in export from nucleus Enzyme cuts after AAUAAA sequence poly A tail 3. RNA splicing – introns removed & exons spliced together • consensus sequences mark intron/exon boundary • snRNPs bind on or near to consensus sequences • additional proteins combine with snRNPs to form a spliceosome that cuts mRNA & joins exons • introns are degraded • TAP protein binds to mature mRNA; allows exit Chromatin exists in 2 forms: • Euchromatin – stains lightly; contains DNA that is transcribed into mRNA. • Heterochromatin – stains darkly; is not transcribed. Ex. Barr body of ♀ mammals – one X chromosome in each cell of ♀ is inactivated early in embryonic development # Barr bodies = # Xs XX ♀ - 1 Bar body XY ♂ – 0 XXX ♀ – 2 XXY ♂ - 1 2. Transcriptional control Rate is determined by transcription factors, repressors & activators. 3. Pre-mRNA processing control Different mRNAs can be made from same gene by alternative splicing of pre-mRNA. 5. mRNA stability control Not all mRNAs have same life span – are broken down in cytoplasm by ribonucleases and micro RNAs 6. Translational control Conditions within cell can  or  protein synthesis