Ch. 5 Part 2 Mitosis

Mitosis  Division of the nucleus that results in two genetically identical daughter cells with the EXACT same number of chromosomes as the parents cell

Important Structures  Centromere  Visible constriction on chromatid  Site of attachment for spindle microtubules  Narrow region of chromatid; region that holds together two chromatids; location on chromosome varies with chromosome  Needed for separation of chromatids during mitosis  Centrosomes  Organelle in animal cells  Located at each pole of the cell during cell division  Acts as MTOC for construction of spindle  Consists of a PAIR of centrioles surrounded by many proteins  Proteins control production of microtubules 9NOT centrioles)  No centrosomes in plant cells

Important Structures  Kinetochores Structure  Found during metaphase on each chromosome  One on each chromatid  Made of protein molecules that bind specifically to:  DNA in the centromere  Microtubules  Bundles of microtubules are referred to as SPINDLE FIBERS  Constructed BEFORE nuclear division starts (S Phase)  Lost after nuclear division  Kinetochore Function  Microtubules attached to each kinetochore PULL kinetochore and chromatid TOWARDS POLE  Microtubules shorten at the POLE END to the kinetochore end

SPINDLE FIBER construction  Microtubule Organizing Center (MTOC)  Consists of the centrosome  Constructs the spindle fibers (made of microtubules)  60-70% of spindles that extend from centrosome are NOT attached to kinetochore  Attachment is random process

Prophase  50-60% of time  Chromosomes become visible  Centrioles develop in cytoplasm near nuclear envelope  Centrioles separate and migrate to opposite ends of nuc. Env.  Centrosome  Region where Centrioles are found  Organize the “spindle”  Fan like microtubule structure that helps separate chromosomes  Plants do NOT have Centrioles Early Prophase: Centrosomes replicate just before prophase Chromosomes start to appear as chromatin coils up (becomes shorter and thicker)  visible Centromere has attached kinetochores Nuclear envelope INTACT Late Prophase: Nuclear envelope disappears (breaks up into small vesicles) Nucleolus disappears Centrosomes move to opposite ends  create POLES of the spindle

End of prophase  Chromosomes coil together tightly  Nucleolus disappears  Nuclear envelope breaks down

Metaphase  Few minutes  Chromosomes line up in middle (M in metaphase  MIDDLE)  Microtubules connect centromere of each chromosome to the 2 poles of spindle METAPHASE: Each centrosome reaches pole Centrosomes help organize production of spindle microtubules Chromosomes line up across equator of spindle Chromosomes attached to spindle by centromere

Anaphase  Centromeres joining sister chromatids separate and become individual chromosomes  They are dragged by fibers to opposite poles  Ends when chromosomes stop moving ANAPHASE: Chromatids move to opposite poles Centromeres move towards poles first, being pulled by microtubules

Telophase  Opposite of prophase  Condensed chromosomes disperse into tangle of material  Nuclear envelope reforms  Spindle breaks apart  Nucleolus becomes visible  At the end  2 identical nuclei in one cell Telophase: Nucleolus reforms Nuclear envelope reforms Chromatids at poles of spindles Uncoil In plant cell…CELL PLATE forms (will become cell wall…made of cellulose) Remains of spindle break down Cytokinesis begins to occur (division of cytoplasm)

Cytokinesis  Happens at the same time as Telophase  Division of cytoplasm  Animal Cells  Cell membrane drawn inward until it pinches off and forms 2 id daughter cells  Plant Cells  Cell plate forms between nuclei  Cell Plate develops into separate membrane  Cell wall appears