Cell Shape and Movement: Cilia & Flagella

Cell Shape and Movement: Cilia, Flagella & Mitosis

• Microtubule Structure and Function: Cilia and flagella are important for cell movement. They are composed of microtubules.
• Cilia: Move materials across the surface of cells. Example: ciliated epithelium.
• Flagella: Propel cells through liquid. Example: sperm and Chlamydomonas.
• Cilia and Flagella Structure: Composed of microtubules arranged in a 9 + 2 pattern. Nine outer doublets and two central microtubules.
• Dynein Arms: Protein motors that drive the movement of cilia and flagella by causing sliding of microtubules. Power stroke and recovery stroke are two parts of dynein action. Dynein arms generate the movement of the cilia/flagella.
• Microtubule Arrangement: The 9 + 2 structure of cilia and flagella is seen in cross-sections.
• Basal Body: The base of cilia or flagella, similar in structure to centrioles, and is essential for their development.
• Centriole Structure: 9 triplet microtubules arranged in a ring structure. Part of the cytoskeleton.
• Microtubule Dynamics: Microtubules are dynamic structures that can grow and shrink. This dynamic growth and shrinkage is important for the function of cilia/flagella.

Mitosis

• Mitosis: Cell division process in which a single cell produces two identical daughter cells.
• Cell Cycle: Ordered series of events that occur from cell formation to cell division. Stages include G1, S, G2, mitosis, cytokinesis.
• Checkpoint Control Important for monitoring and regulating stages of the cell cycle to prevent errors.
• Mitosis Phases: Interphase, Prophase, Prometaphase, Metaphase, Anaphase, Telophase, Cytokinesis.
• Interphase: The phase before mitosis, characterized by cell growth, DNA replication, and protein synthesis
• Prophase: Chromosomes condense, spindle formation begins
• Prometaphase: The nuclear envelope breaks down, microtubules attach to kinetochores.
• Metaphase: Chromosomes align at the metaphase plate.
• Anaphase: Sister chromatids separate and move to opposite poles.
• Telophase: Chromosomes decondense, nuclear envelope forms around each set of chromosomes
• Cytokinesis: Cytoplasm divides, creating two separate daughter cells.
• Organelle Inheritance: Organelles are distributed to each daughter cell during mitosis.
• Cytokinesis and Actin-Myosin Contraction: A contractile ring of actin and myosin proteins forms at the equator of the cell to pinch the cell in two during cytokinesis. For cells that do not have a cell wall, like animal cells.
• Centrosome Duplication: The duplication of the centrosome is essential for the proper formation of a mitotic spindle for mitosis.
• Microtubules (MTs): Important components of the mitotic spindle, connecting centrosomes to chromosomes.
• Three distinct classes of Microtubules: Kinetochore MTs, Astral MTs, Interpolar MTs, each having diverse roles in aligning and separating chromosomes.
  • Kinetochore MTs: Attach to the kinetochore, essential to move chromosomes.
  • Astral MTs: Extend to surrounding cytoplasm, important for positioning the spindle apparatus, and for chromosome positioning.
  • Interpolar MTs: Connect the two spindle poles. Contribute to spindle length, structure and separation.
• Spindle Checkpoint Proteins: Regulates the cell cycle, ensuring that all chromosomes are correctly attached to the mitotic spindle before sister chromatids separate, preventing chromosome missegregation
• DNA Condensation in Mitosis: DNA coils tightly and compactly to form chromosomes that can move efficiently, during mitosis and meiosis.
• Nuclear Envelope Breakdown: The breakdown of the nuclear envelope allows microtubules to access chromosomes for proper segregation.
• Kinetochore Micro tubule Attachment: Kinetochores attach to kinetochore microtubules and are critical for chromosome segregation.