Cell Bio Review 1,000,000 David Pearce

3 Prophase I Leptotene – chromatin begin to condense, 2 sister chromatids so close, cannot be distinguished Zygotene – synapsis – synaptonemal complex Pachytene – bivalent – tetrad – Recombination Diplotene – Synaptonemal complex disappears – Bivalents begin to separate but held together at centromeres and ~ 50 points of crossing over – chiasmata Diakinesis – stage of max condensation

4 Homologous chromosomes exchange segments during crossing over Crossing over occurs during Pachytene During meiosis in males, the X and Y chromosomes form a bivalent and exchange information in the pseudoautosomal regions

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RNA Polymerase produces a complementary RNA to the template strand The template strand of DNA serves as a template for RNA formation during transcription – Sometimes called the Antisense strand The coding strand is not directly involved in transcription. – Sometimes called the Sense strand – The coding strand sequence is extremely similar to the single-stranded RNA molecule Coding strand has T RNA sequence has U instead of T 7

8 Prokaryotic Termination of Transcription – Rho dependent Rho factor, an ATP- dependent unwinding factor binds to specific termination sequence and unwinds RNA from DNA template – Rho independent Formation of a GC-rich hairpin loop forms and pulls RNA away from DNA

Rifampin and Actinomycin: Two Antibiotics that Inhibit Transcription Rifampin specifically inhibits initiation of RNA synthesis in BACTERIA Interferes with formation of 1 st few phosphodiester bonds in RNA chain – semisynthetic derivative of rifamycins, derived from strain of Streptomyces. – Used to treat TB (tuberculosis) Actinomycin D binds tightly to dsDNA, prevents it from being effective template for RNA synthesis in both pro and eukaroytes – Polypeptide antibiotic from different strain of Streptomyces, – Used infrequently in treatment of various malignant neoplasms: Wilm’s tumour, sarcomas. – Adverse effects: bone marrow depression, GI toxicity; it is extremely irritating, produces severe tissue damage (toxic reactions frequent and severe)

10 Eukaryotic RNA Polymerases RNA Polymerase I, II, and III carry out transcription in the eukaryotic nucleus – RNA Polymerase I: Precursor for 28S, 18S and 5.8S rRNAs – RNA Polymerase II: Pre-mRNA, snRNA and microRNAs – RNA Polymerase III: Pre-tRNA, 5S rRNA

11 Steps in RNA Pol II TF binding TFIID binds to TATA box Can bind to DPE sequence in case of DPE- driven promoters RNA Polymerase II recruited to promoter with TFIIF attached Pol II Large Has a C terminal repeat on C- terminal domain Phosphorylation State of CTD important for Active TFIIH has both helicase and protein kinase activity Pol II phosphorylated by TFIIH at CTD

Ribosomal RNA rRNA participates in protein synthesis as part of ribosome (RNA + protein complexes) Prokaryotes: 70S ribosome – Small subunit = 30S Small subunit composed of 16S rRNA and 21 proteins – Large subunit = 50S Large subunit composed of 23S + 5S rRNA subunits, and 32 proteins Eukaryotes: 80S ribosome – Small subunit = 40S Small subunit composed of 18S rRNA and ~30 proteins – Large subunit = 60S Large subunit composed of 28S, 5.8S and 5S rRNA and ~ 50 proteins

13 Splicing Exons: sequences destined to appear in final mRNA Introns: sequences within the primary transcript that do not appear in mature, functional RNA Splice sites 5’-GU with 3’ AG – Splice Donor: GU at the 5’ boundary of the intron – Splice Acceptor: AG at the 3’ boundary of the intron – Branch Point: A