Lecture 13: Mitosis PDF

Lecture 13: Mitosis Readings: Ch. 9.1-9.6  Learning Objectives Know the difference between mitosis and meiosis Know the stages of mitosis Understand how the cell cycle is regulated Know the purpose of checkpoints in the cell cycle  Every time a cell divides: 1) its...

Lecture 13: Mitosis Readings: Ch. 9.1-9.6  Learning Objectives Know the difference between mitosis and meiosis Know the stages of mitosis Understand how the cell cycle is regulated Know the purpose of checkpoints in the cell cycle  Every time a cell divides: 1) its DNA is duplicated, and 2) the DNA divided evenly between parent and daughter cell Mitosi Meiosi s s The Cell Cycle M This is where cell division happens  Cell Cycle (Mitosis) G1 – first gap Interphase S – synthesis of DNA consists of G1, S, and G2 G2 – second gap M – mitosis and cytokinesis G0 – substitutes for G1 for M cells postponing division or never dividing again Gap phases allow the cell to: Grow large enough Synthesize enough organelles for daughter cells  The Cell Cycle (Mitosis) S: Cell replicates DNA G1: Cell is preparing to replicate DNA  The Cell Cycle (Mitosis) S: Cell replicates DNA G1: Cell is preparing to G2: Cell prepares to replicate divide DNA M: Cell divides  Cytokinesis In most cases, mitosis is quickly followed by cytokinesis Two nuclei are segregated into separate daughter cells Process is different in animals and plants Animals – cleavage furrow constricts like a drawstring to separate the cells Plants – cell plate forms a cell wall between the two daughter cells Ultimate result of mitosis and cytokinesis is production of two daughter cells with the same  Decision to divide External factors Environmental conditions Signaling molecules (ex: hormones) Internal factors Cell cycle control molecules Checkpoints  Control of the Cell Cycle Cell-cycle length can vary greatly among cell types G1 phase is essentially eliminated in rapidly dividing cells Epithelial cells of intestines Nondividing cells get permanently stuck in G1 phase This arrested stage is called the G0 state Example: Nerve cells  Checkpoint proteins Cyclins and cyclin-dependent kinases (cdks) responsible for advancing a cell through the phases of the cell cycle Amount of cyclins varies through cycle Cdks are kinases controlling cell cycle Must bind to a cyclin to be active  Three checkpoints Critical regulatory points Three checkpoints in eukaryotes: G1 checkpoint (restriction point) G2 checkpoint Metaphase checkpoint Checkpoint proteins act as sensors to determine if the cell is in proper condition to divide Cell cycle is delayed until problems fixed (or prevented altogether) Loss of checkpoints can lead to mutations and cancer G1 Checkpoint: G2 Checkpoint: M Checkpoint: Checks if conditions are good for Checks DNA condition Checks Chromosome division All of DNA replicated? attachments Do we have enough Any DNA damaged? Are all chromosomes nutrients? Are the protein levels good? attached to a spindle Mitosis-Promoting Factor Induces Mitosis Mitosis-promoting factor (MPF) Is present in the cytoplasm of M-phase cells Induces mitosis in all eukaryotes  How is MPF turned off? Anaphase: Enzyme complex activated by mitosis degrades MPF cyclin subunit Negative feedback: process slowed or stopped by one of its products E.g. Thermostat: shuts down furnace when temp it high  Both phosphates present until late in G2 phase when one removed Cancer: Out-of-Control Cell Division Cancer Is a common, sometimes lethal disease Is a complex family of diseases caused by cells that: Grow in an uncontrolled fashion Invade nearby tissues Spread to other sites in the body Types of Cancerous Cell Defects Cancerous cells have two types of defects: 1.Defects that make the proteins required for cell growth active when they should not be 2.Defects that prevent tumor suppressor genes from shutting down the cell cycle