Ch. 5 Part 2 Mitosis. Mitosis Division of the nucleus that results in two genetically identical...
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Transcript of Ch. 5 Part 2 Mitosis. Mitosis Division of the nucleus that results in two genetically identical...
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
Remember: PMAT
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