CBIO 3400 Week 12 Study Questions 1 Chromosome segregation is an important event during mitosis How does a cell ensure that daughter cells receive a full set of chromosomes 1 DNA replication origins 2 centromere primary constriction on chromosome required for mitotic segregation centromeric DNA forms centromere 1 CENP A H3 variant binds CBF3 complex 2 CBF3 complex recruits Ndc80 Dam1 which initially bind MT s side but finish as end attachment on MT 3 Form mitotic spindle from these kinetochore proteins Ndc80 Dam1 mitotic spindle checkpoint 3 telomeres protein DNA complexes at ends of linear chromosomes containing telomeric sequences G rich TTAGGG ds repeats T loop bound by TRF1 TRF2 Telomere Repeat Factor other proteins recruited ss DNA D loop 3 overhang bound by Pot1 Protection Of Telomere T loop D loop structure that protects telomere The mitotic spindle checkpoint prevents a cell from leaving metaphase starting anaphase before 2 conditions are met for the sister chromosomes 1 under tension 2 attached to opposite spindle poles Attachment of sister chromosomes at opposite spindle poles is key to ensuring that daughter cells receive a full set of chromosomes 2 Describe how DNA is packed in the nucleus starting from DNA double helix short region of DNA double helix nucleosomes beads on a string form of chromatin 30 nm chromatin fiber of packed nucleosomes section of chromosome in extended form section of chromosome in condensed form only makes up a small section of entire mitotic chromosome 3 What are exons and introns Does one gene always encode one protein If not explain the reason Exons sequences in protein coding segment of mRNA that originated from the gene still present in mature mRNA encode small polypeptides CAN code for protein domains immunoglobin has several structural domains in exons EX protein domains of antibody specified in exons Introns sequences present in genes absent in mature mRNA increase length of genes 1 this info is lost during maturation of pre mRNA i e spliced out of pre mRNA during maturation frequently contain STOP codons in at least 1 reading frame for protein encoded by gene comprise 90 of protein coding sequences One gene can encode many proteins due to exon shuffling alternative splicing Exon Shuffling having introns b tw exons increases distance b tw exons therefore increases the likelihood of exon recombination evolutionary time scale occurs at DNA level exons from different genes can be combined joined to form a new gene can produce proteins w different functions EX LDL receptor 18 exons 9 related to EGF pre cursor 5 related to C9 complement 3 unique Alternative Splicing introns have various splicing patterns allowing 1 pre mRNA to give rise to multiple proteins happens in real time 1 pre mRNA gives rise to multiple proteins exons from 1 pre mRNA are joined in different combos cell type specifies combo of exons used EX tropomyosin gene 1 tropomyosin gene gives rise to many different tropomyosin proteins w different functions 4 Describe the structure of a core promoter shortest sequence of DNA that directs transcription modular has 1 or more of 4 sequence blocks 1 initiator Inr consensus Py 2CA Py 5 located 3 to 5 recognized by TFIID Transcription Factor II other proteins 2 TATA box consensus TATAAAA located 25 to 35 binding site for TBP TATA Binding Protein 3 BRE Transcription Factor IIB TFIIB Binding Element recognized by TFIIB 4 DPE Downstream Promoter Element 5 How is RNA transcription initiated 1 TFIIF has an ATP dependent helicase in RAP70 subunit that unwinds duplex DNA to form an 2 TFIIF RAP30 subunit tightly binds RNA pol II this is important for recruitment of RNA pol II to open complex pre initiation complex 3 TFIID makes contacts with core promoter 4 TFIIA binds TFIID promoter complex which increases TBP s affinity for TATA box 5 TFIID promoter complex binds TAF TBP Associated Factor 2 6 TFIIB is a bridging protein that brings RNA pol II to promoter TFIIB binds RNA pol II TFIID promoter complex TFIIB helps orient RNA pol II to select start site 7 TFIIE binds RNA pol II recruits TFIIH to open complex 8 TFIIH has a Cdk7 kinase subunit that phosphorylates CTD C Terminus Domain of RNA pol II on serines this marks that RNA pol II has cleared promoter 6 How does chromatin rearrangement affect gene expression Chromatin rearrangement can change the order of introns exons in the gene thus alter which proteins are eventually synthesized the order of the introns exons determines protein function Alternative splicing exon shuffling Or something else 3
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