Mitosis L13 Slides F24 PDF

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Need to have computer screen facing us on BRIGHT MODE, need to put Canvas on full screen The only software app running must be Canvas. No other apps/windows can be running, including messaging apps. We can see whether you move away from Canvas in the log-files. Do not highlight any text on your Canvas site! Phones, smart watches, calculators etc. must be turned off and remain in backpacks until 1:15 Colored paper sheet can be used as scrap paper. Do not write on it before the exam starts. You are not allowed to leave your seat during the prelim, unless it is an emergency Once you start the exam, you will have 45 minutes to finish. Once you are finished and ‘submit’ the exam, you must close your laptop or turn your tablet upside down. If you finish your prelim before 1 pm, you may leave the room. Show your quiz submission page at the room EXIT and return your scratch paper. After 1 pm, remain seated in EXAM MODE - NO PHONES! - until 1:15,  Mitosis Reading: ECB5 625-63 Learning Objectives: Understand the organization of microtubules in the mitotic spindle and which associate with centrosomes and kinetochores Understand the events that occur in each phase of mitosis Understand how chromosomes become attached to appropriate microtubules: ‘bi- orientation’ Understand how the checkpoint in mitosis (spindle-assembly Synchronous mitoses in the fruit fly embry checkpoint) is satisfied Today’s topics 1. Overview of events in M-phase and preparation for M-phase 2. Prophase and the mitotic spindle 3. Chromosome attachment in prometaphase and the spindle-assembly checkpoint in metaphase 4. Anaphase: separation of chromosomes 5. Telophase and cytokinesis  The cell cycle is divided into four phases Growth and preparing for M PHASE (Growth and Figure 18-2 Essential Cell Biology preparing for S PHAS o events in interphase set the stage for M-pha During S-phase: The genome is replicated (duplicated) by DNA polymerase. During replication, cohesin proteins bind to the genome and form rings that hold the duplicated “sister chromatids” together Sister chromatids are two exact copies of the same chromosome. They each consist of DNA and histone proteins (chromatin). o events in interphase set the stage for M-pha The centrosome is replicated (duplicated) during S and G2 phases. Centrosomes are MTOCs (microtubule organization centers) composed of g-tubulin complexes that At nucleate microtubules the end of interphase: Duplicated and decondensed chromosomes held together by cohesins Microtubules play a critical role in chromatid segregation!  The cell cycle is divided into four phases Growth and preparing for M PHASE (Growth and Figure 18-2 Essential Cell Biology preparing for S PHAS hase consists of two distinct, but overlapping p mito cytokine sis sis MITOSIS: The precise and equal segregation of the duplicated chromosomes by the microtubule-based mitotic spindle, resulting in two nuclei CYTOKINESIS: The division of the cytoplasm in two halves to generate two cells.  Overview of the 5 stages of mitosis mitosis Prophase Metaphase Telophase Cytokinesis Prometaph Anaphase ase Animal cell: Movie 18.5 Essential Cell Biology Today’s topics 1. Overview of events in M-phase and preparation for M-phase 2. Prophase and the mitotic spindle 3. Chromosome attachment in prometaphase and the spindle-assembly checkpoint in metaphase 4. Anaphase: separation of chromosomes 5. Telophase and cytokinesis  During prophase, the ‘mitotic spindle’ begins to form and chromosomes condense e mitotic spindle begins to form outside the nucleus (more on that in a The kinetochore also assembles during prophase (more on that in a bit  Condensin proteins form rings that condense chromosomes to facilitate segregation during mitosis Condensin is similar to, but not the same as, cohesin! Both proteins form rings, but they have different functions. Condensin organizes chromatin into loops, resulting in compaction  The Mitotic Spindle The “mitotic spindle” is the protein machinery that segregates sister chromatids into separate nuclei. It is made of microtubules, motors, and the two centrosomes. (all the green stuff in the figure below) Has a built-in quality control system (the spindle-assembly checkpoint) (spindle assembly checkpoint) ProphasePrometaphaseMetaphase Anaphase Telophase Cytokinesis  Microtubules Review 13 protofilaments + + + -- + + - - + + Favore d for + growt + + + + + h - + + -- + - - - + + + + + + + + Figure 17-8, 17-9 Essential Cell Biology Associated with centrosome/spindle pole itotic spindle contains three classes of microtu Plasma membrane Each centrosome in the mitotic spindle is called a “spindle pole” Each spindle pole with its collection of microtubules is called an “aster” h of these three classes of microtubules has a different function (will see this lat Figure 18-24, Essential Cell Biology Today’s topics 1. Overview of events in M-phase and preparation for M-phase 2. Prophase and the mitotic spindle 3. Chromosome attachment in prometaphase and the spindle-assembly checkpoint in metaphase 4. Anaphase: separation of chromosomes 5. Telophase and cytokinesis  During prometaphase, the nuclear envelope breaks down and microtubules begin attaching to chromosomes Phosphorylation of nuclear lamins (intermediate filament proteins) and nuclear pore proteins, causes the nuclear envelope to break down into vesicles Microtubules begin attaching to kinetochores.  The kinetochore links centromeres to kinetochore microtubules mere: special region of DNA within each chromosome that the kinetochore att chore: a protein complex that links microtubules to the centromere of each ch Cohesins holding chromatids together Figure 18-24, 18-25 Essential Cell Biology During metaphase, the chromosomes are arranged on the “metaphase plate” (midway between spindle poles) How does this occur??? Tension creates a stable bipolar attachment Tension stabilizes the microtubule-kinetochore attachments! Only the correct bipolar attachment has tension across the Figure 17-39 Molecular Biology of the Cell kinetochores The Spindle-Assembly Checkpoint: Are All Chromosomes Attached? NO! Wait! (Spindle-assembly checkpoint)  The Spindle-Assembly Checkpoint: Are All Chromosomes Attached? YES! OK, now all chromosomes are bi-oriented. Checkpoint satisfied!  Activation of the Anaphase Promoting Complex (APC/C) leads to degradation of M-cyclin and cohesin proteins M- M- Spindle-assembly checkpoint UBIQUITYLATION AND DEGRADATION OF APC/C M-CYCLIN /C Summary of the Spindle Assembly Checkpoint Cohesins holding chromatid s together When properly connected to both spindle poles, the kinetochore microtubules pull on the kinetochores – cohesins hold the chromosomes together. Any unattached kinetochore sends out a signal preventing exit from metaphase by preventing activation of APC/C When all kinetochores are attached to appropriate microtubules, this satisfies the checkpoint, which leads to the activation of the Anaphase Promoting Complex (APC/C) Activation of APC/C leads to the degradation of M cyclin, thereby Today’s topics 1. Overview of events in M-phase and preparation for M-phase 2. Prophase and the mitotic spindle 3. Chromosome attachment in prometaphase and the spindle-assembly checkpoint in metaphase 4. Anaphase: separation of chromosomes 5. Telophase and cytokinesis ng anaphase the sister chromatids are pulled a Two processess occur simultaneously in anaphase: They are named: Anaphase A Anaphase B  Anaphase A Chromosome not shown Microtubule depolymerization at the kinetochore pulls the chromosome to the pole Anaphase B Interpolar MT ‘push’ Kinesin 5 a double-headed motor! Astral MT Cell Dynein Membran e ‘pull’ Today’s topics 1. Overview of events in M-phase and preparation for M-phase 2. Prophase and the mitotic spindle 3. Chromosome attachment in prometaphase and the spindle-assembly checkpoint in metaphase 4. Anaphase: separation of chromosomes 5. Telophase and cytokinesis  During telophase the nuclear envelopes reassemble and cytokinesis begins Nuclear envelopes form around each set of chromosomes to produce two nuclei Cytokinesis is initiated (in animal cells the contractile ring begins to form) During cytokinesis the cell completes the division process by separating the cytoplasm  Cytokinesis nesis in animal cells: contraction of the actin-based contrac Plant cell: Movie 18.4 Essential Cell Biology