BIO 151 1nd Edition Lecture 17 Outline of Last Lecture - DNA Replication- DNA Replication enzymes - Leading/Lagging enzymes- Polymerase Chain Reaction- Replication accuracyo Fixing DNA defectsOutline of Current Lecture - Gene to trait- Overview of Transcriptiono Why Transcribe DNA- DNA vs RNA- mRNA processing- Alternative splicingCurrent Lecture- From Gene to trait: How do we go from DNA to traito Central dogma: first introduced by Watson and Cricko DNAtranscribed RNAtranslated proteintrait- Overview of processo Transcription: synthesis of messenger RNA (mRNA) using DNA template mRNA catalyzes message from DNA to machinery that makes protein o Translation: ribosomes convert mRNA to amino acids to form polypeptideo Why translate RNA? Increase copy number  Preserve original info Give cell ability to control gene expression- Cell has more control over expression of genes- Cell needs to figure out when and how much of protein it needs- Gene expression as a way for cells to fine tune its needs/uses of protein Where does it happen?- Bacteria cell: Cytoplasm- Eukaryotes: nucleus  ribosomesThese 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. DNA vs. RNA- DNA has thymine (T), RNA has uracil (U)- Pentose sugar is ribose for RNA and deoxyribose for DNA- RNA is single stranded- Transcription (DNARNA)o Transcription unit: where process begins to where it ends Promotor: transcription starts, upstream of transcribed region Terminator: transcription stops; down stream of transcribed region.o Stages: Initiation: - RNA polymerase: separates DNA, binds to promotor Elongation: prime and extend mRNA 5’  3’- move along template strand 3’5’ Termination: completed RNA transcript- Upstream to down stream- RNA floats around nucleuso Transcription is different from replication Only 1 strand is read: “template strand” Unidirectional (replication has to replication forks) Clearly marked endo Closer look Promotor: has repetitive TATA sequence as look upstream from start point- TATA box: recruits transcription factors that bind to DNA Flanking sequence; recruits other transcriptive factorso Transcription factors recruit RNA polymeraseo RNA polymerase in between two strands in order to transcript- Transcription initiation complex: transcription factors, RNA transcription, RNA polymerase IIo ~10% of genes code for transcription factorso This gives the cell ability to control gene- Termination of transcriptiono Terminator sequence: DNA reads TTATTT…RNA polymerase translates a polyadenylation signal: AAUAAA Clevage proteins: bind to AAUAAA 10-30 nucleotides downstream, the RNA polymerase stops transcribing and releases mRNAo Transcription in Action Transcription factors bind promotor and recruit RNA polymerase Transcription initiation complex activated…RNA polymerase unzips and reads DNA template to transcribe RNA 5’ to 3’o Activator proteins: signal complex to go- In RNA processing: capping and tailyo Pre mRNA problems Unstable Extra infoo Protect mRNA at each end  fixes problem of instability Add 5’ cap: modified G (protect mRNA at 5’ end) Add 3’ poly-A tail: string of adenines- Critical for exporting mRNA from nucleus, stabilizing mRNA, attaching to ribosome o mRNA processing: splicing (rids of extra info) introns cut out and exons spliced together Exons: make up final mRNA, code for amino acids Introns: discarded from final mRNA Splicing: remove introns, join exons- Donor/acceptor complexes Spliceosome: enzyme that catalyzes splicing- Made of protein and small nuclear RNAs (snRNA)- snRNAs bind donor and acceptor sequence- break 2 covalent bonds, form new covalent bonds- Alternative splicing generates protein diversityo More than 1 protein product is made from 1 gene!o Most vertebrate genes undergo alternative splicingo mRNA sequence tells the spliceosome how to splice  protein