Lecture 6

• The room selection is not up to the instructor and the room changes are not up to the instructor
• Student feedback and course evaluations are important to improve courses, particularly if the student has more university left
• The instructor can never see who wrote what or the comments until after the marks are due, and it is always anonymous
• The instructor can see the response rate and wants to get the response rate higher than 31%
• The cell cycle is conserved in all eukaryotes and is a sequence of events where the contents of the cell are duplicated and divided into two
• Cell division


  1. Cell growth and chromosome duplication

  2. Chromosome segregation

  3. Formation of two daughter cells
• Cells in culture do not divide at the same time, but when they do divide, they all follow the same stages of mitosis
• Interphase


  The period between cell divisions where there is regular metabolic activity, cell growth, and repair
• S phase


  DNA replication
• G1 and G2


  Before and after S phase, respectively
• Mitosis is not the same as DNA replication, they are separate processes
• M phase includes both mitosis and cytokinesis
• Types of cells in multicellular organisms

  • Mature cells that do not divide
  • Cells that divide only with appropriate stimulus
  • Cells that normally divide on an ongoing basis
• G0


  A state where cells are not dividing but are still carrying out their functions
• Cell cycle control system

  • Has three major checkpoints: start checkpoint, G2/M transition checkpoint, and metaphase to anaphase checkpoint
  • Checkpoints delay later events until earlier events are complete
• Start checkpoint


  Decides whether to enter S phase based on environmental conditions
• G2/M transition checkpoint


  Checks if DNA replication is complete and DNA damage is repaired before entering mitosis
• Metaphase to anaphase checkpoint


  Checks if chromosomes are properly attached to the mitotic spindle before allowing chromosome segregation
• Cyclin-dependent protein kinases (CDKs)


  Molecular switches that control entry into the next phase of the cell cycle
• Entry into each phase of the cell cycle is triggered by the activation of specific CDKs
• Cell cycle progression is paused at checkpoints by regulators that inhibit the activation of CDKs
• The remainder of the lecture will focus on what happens during mitosis and cytokinesis
• them and that's how the system works so hopefully you understand the big concept looks like the recording is is working they transferred it over so so uh hopefully that that's good for you this is one of those things you do not need to sit down and memorize the details here if you understand and remember the last couple of slides right and and that's I think the difference uh as you're stting to the final for the final is that some students feel like oh I got to memorize every single thing I got to brute force it but then other students are like well I I kind understand what's going on then then this is all very obvious as to what happens right and these details in the yellow here they're a bit too much
• Cell control system in its General view
• Mitosis is the nuclear division, Cytokinesis is the cytoplasmic division
• Mitosis and Cytokinesis overlap, with cytoplasmic division starting before nuclear division is complete
• Prophase


  1. Nucleus removed

  2. Mitotic spindle forms

  3. Chromosomes condense
• Prometaphase


  1. Mitotic spindle forms further

  2. DNA moves towards the middle
• Metaphase


  Chromosomes at the middle
• Anaphase


  Chromosomes pulled apart
• Telophase


  Nucleus reforms
• Cytokinesis


  Cytoplasmic division
• Interphase has G1, S, and G2 phases
• In interphase, centrosome duplication is initiated and completed by G2
• In interphase, chromosomes are replicated but still decondensed
• Cohesin


  Proteins that hold sister chromatids together
• Condensin


  Proteins that condense chromosomes
• Centromere


  Region where sister chromatids are attached
• Centrosome


  Microtubule organizing center, contains centrioles
• Gamma tubulin ring complexes

  Nucleate and stabilize microtubule minus ends