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