BIOL 3510 1st Edition Lecture 23 Outline of Last Lecture I Roles of Actin Networks II Microfilament Growth and Disassembly III Actin in Action IV Resting and Contracting Muscle Cells Outline of Current Lecture I Intro to Cell Cycle II G1 Phase III Control of S Phase IV Prophase V Prometaphase Current Lecture Cell cycle duplication and division of a cell and its contents The cell cycle has four phases 1 2 3 4 G1 phase Gap Cell growth S phase synthesis DNA replication G2 phase Gap Cell growth M phase mitosis and cytokinesis Progress through the cell cycle controlled by the cell cycle control system Cyclin dependant kinases Cdks are major components of the cell cycle control system Cdk kinase that activates cell machinery constant amount cyclical activation Cyclin activates a Cdk cyclical amounts Cyclin concentrations are regulated by transcription and proteolysis Transcription gradual increase in cyclins Proteolysis quick decrease in cyclins APC anaphase promoting complex These 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 In addition to cyclins Cdks are regulated by phosphorylation dephosphorylation and inhibitory proteins Different Cdk cyclin combos trigger different cell cycle events G1 Phase At the end of M all S Cdks and M Cdks are inactivated by cyclin degradation and inhibitor protein activation In mammalian cells mitogens promote cyclin transcription needed for entry into S phase Mitogens promote cell division by activating G1 Cdk and G1 S Cdks which inactivate Retinoblastoma Rb proteins Cell cycle progression is paused if the DNA is damaged or incompletely replicated 1 Inactivation of G1 S and S Cdks during G1 and S by p53 activation pauses the cell cycle o DNA repair or cell death o No p53 leads to the replication of damaged DNA promoting cancer Centrosome cycle centrosome duplication initiated in G1 is triggered by G1 S Cdk and S Cdk Control of S phase initiation of replication 1 DNA synthesis is initiated at origins of replication 2 Pre existing origin of recognition complexes OCRs recruit Cdc6 to origins of replication during G1 3 Helicase binding generates the prereplicative complex pre RC 4 Activation of S Cdk a Activates helicases causing the assembly of the remainder of the replication fork b Phosphorylates Cdc6 targeting it for degradation preventing re replication Sister chromatids are held together by cohesion ring complexes until anaphase Activation of M Cdk by Cdc25 leads to entry into M phase M Cdk is activated at the end of G2 6 Stages of Mitosis Prophase phosphorylation by M Cdk triggers formation of condensing complexes that condense chromosomes Increased MT dynamic instability and spindle formation is triggered by phosphorylation of MAPs by M Cdk Motor proteins and MAPs crosslink interpolar microtubules forming the mitotic spindle Prometaphase breakdown of the nuclear envelope begins with the M Cdk dependent phosphorylation of nuclear pore proteins and lamins Microtubules connect to the centromeres of sister chromatids via kinetochore protein complexes There are three types of microtubules in a spindle Bi orientation of kinetochore microtubules generates tension Chromosomes line up on the metaphase plate via the action of dynamic instability and motor proteins Prometaphase alignment period Metaphase begins when the chromosomes are aligned on the metaphase plate
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