12 mitosis - Objectives 1 To know how a single eukaryotic...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Objectives 1. To know how a single eukaryotic cell divides into two daughter cells 2. To recognize some of the remarkable features of different phases during a nuclear division 3. To understand the mechanism of chromosome translocation inside a dividing cell 1 Nuclear and Cell Division • M phase: A. Nuclear division (mitosis) B. Cytoplasmic division (cytokinesis) 2 Mitosis • • Changing appearance and behavior of chromosomes To ensure that each of the 2 daughter nuclei receives 1 copy of each duplicated chromosomes Divided into different phases: 3 • 4 A. Prophase Nucleus: 1. 2. Nucleoli disperse Chromosomes start to condense as visible discrete objects (to prevent tangling during distribution of chromosomal DNA) Each chromosome consists of 2 sister chromatids attached to each other at centromere 3. 5 Cytoplasm: 1. A small zone of granular material located adjacent to nucleus (centrosome organizing center for mitotic spindle assembly) 2. The pair of centrosomes (duplicated (duplicated during S phase) separate from each other and move toward opposite poles 3. A structure formed by microtubules stretching between the opposite poles (mitotic spindle), guiding chromosome movement 6 Centrosome Procentriole(s) The Centrosome Cycle 7 B. Prometaphase 1. Breakdown of nuclear envelope 2. Spindle microtubules enter nuclear area and make contact with chromosomes • A special type of DNA sequence at centromere of chromosome (CEN sequences) - A plate-like, 3-layered protein structure attached to CEN sequences (kinetochore) 8 (a Kinesin) 9 • 3 types of spindle microtubules: a. Attached to kinetochores (kinetochore microtubules) b. Interact with microtubules from opposite poles (polar microtubules) c. Shorter ones; form asters at each pole; interact with proteins lining plasma membrane (astral microtubules) 10 (astral microtubules) (kinetochore microtubules) (polar microtubules) 11 12 C. Metaphase • Maximally condensed chromosomes aligned at plane equidistant between the poles (metaphase plate) Individual chromosomes can be identified and classified, depending on the differences in size and shape (karyotype) • 13 D. Anaphase • The 2 sister chromatids separate and begin moving toward opposite poles: Kinetochore microtubules get shorter; chromosomes are pulled toward the poles (anaphase A) Polar microtubules lengthen; the poles move away from each other (anaphase B) 14 - 15 16 E. Telophase 1. 2. 3. 4. 5. Daughter chromosomes have arrived at the poles and revert to extended fibers Nucleoli develop Spindle disassembles Nuclear envelopes form Undergoes cytokinesis to divide into 2 daughter cells 17 Cytokinesis • Starts during late anaphase or early telophase • Larger organelles (e.g., ER and Golgi (e.g., complex) → fragmented into small vesicles early in mitosis → reassemble in daughter cells • Mechanism is different in animals and plants: 18 A. Animal cells • A belt-like bundle of actin microfilaments forms beneath plasma membrane during early anaphase (contractile ring) Interaction of actin filaments with myosin molecules The ring tightens around cytoplasm - 19 20 - The cell is divided along a plane that passes through the central region of spindle (spindle equator) • A slight indentation → deepens into a cleavage furrow → encircles the cell → opposite surfaces make contact → the cell is split into two (cleavage) 21 B. Plant cells • Divide by assembling a plasma membrane and a cell wall between 2 daughter nuclei An array of microtubules derived from polar microtubules (phragmoplast), which oriented perpendicular to the new cell wall: 1. Guide small vesicles (containing non(containing cellulose materials) from Golgi complex to and align across equatorial plate 22 2. Fusion of vesicles forming a large flattened sac (cell plate) 3. Expanding cell plate makes contact with original cell wall and thus separates the 2 daughter cells 4. Deposition of cellulose microfibrils 23 Fingerlike tubules from vesicles → fusion of the neighouring vesicles Tubular network Leading edge of the growing network contacts the parent plasma membrane → loses cytoplasmic gaps → becomes a continuous flattened partition (cell plate) 24 ...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online