I. Chromosomes
A. Literally translates as “Colored Body”
B. DNA: Uncoiled, it is too thin to be seen with
light microscope.
C. Chromatin: DNA + Proteins
1. Histones – proteins DNA wraps
around (like spools of thread)
2. Nucleosome – one histone wrapped
with DNA.
Twisted Staircase to “X”
Kinetochore
One
nucleosome
DNA
DNA
histone
core
Fig. 9.9, p. 156-157
I. Chromosomes
D. The “X” is a condensed, duplicated
chromosome.
1. The “X” consists of two sister
chromatids (exact copies of one
another)
2. Connected at centromere (constriction
where microtubules can connect)
D. The “X” is a condensed, duplicated
chromosome.
3. Kinetochore – the protein disc where
SF actually attach
I. Chromosomes
Sister Chromatids, Centromere, Copies
of DNA, Chromosome(s)
II. Mitosis
A. Purpose: To generate Two identical
(Twin) nuclei. To genetically CLONE a
cell.
B. Where in Body?
1. Somatic Cell: Body cells (all except
sperm and eggs, which are sex cells).
2. To generate DIPLOID cells (two copies
of each chromosome, 2n).
II. Mitosis
Stages:
A. Prophase:
1. Cell often loses shape (due to cytoskeleton
disassemblage)
2. Nuclear membrane disintegrates.
3. DNA (sister chromatids) begins condensing.
4. Centrioles (animal cells) duplicate and
move to poles of cell.
5. Spindle fibers (made of microtubule
subunits) begin to assemble from each pole.
Prophase
II. Mitosis
B. Metaphase:
1. Cell elongates as spindle microtubules
overlap in middle.
2. Spindle fibers align chromosomes at
equator.
3. “Meta” translates as middle
Metaphase
II. Mitosis
C. Anaphase
1. Microtubules attached to centromeres
shorten and pull sister chromatids
apart.
2. Other microtubules grow past one
another to further elongate cell.
3. Chromosomes move to poles.
Anaphase
Fig. 9.10, p. 157
II. Mitosis
D. Telophase: (largely opposite of prophase)
1. Nuclear envelop reforms.
2. Chromsomes uncondense.
3. Spindle fibers disassemble.
4. Centrioles move from poles.
Telophase
II. Mitosis
Final Results:
Initial
46 chromosomes
1 cell
Final
Cell Prior to Mitosis
Label
?
III. Cell Cycle
A. Interphase:
1. G1 (Gap 1): Normal cell growth.
2. S phase: Synthesis, DNA replicated
3. G2 (Gap 2): Cell prepares for division.
B. Mitosis: Equal distribution of
chromosomes into two nuclei.
C. Cytokinesis: Division of cytoplasm to
make two cells.
IV. Cancer (Add to Notes)
What is Cancer?
Body cells undergoing excessive mitosis/cell
division.
Fig. 9.3, p. 151
Where in cell cycle?
Interphase:
Mitosis:
IV. Cytokinesis
A. Cell leaves mitosis as 1 cell with 2 nuclei!
B. Cytokinesis is division of cytoplasm
1. Animal Cells: Cleavage furrow forms
as cell constricts.
2. Plant Cells: Cell plate forms as two
cells divide cytoplasm.
cell wall
former
spindle
equator
light micrograph and transmission electron micrograph
showing cell plate formation in a dividing plant cell
vesicles
converging
cell plate
Fig. 9.6, p. 154
Mitosis is
over, and the
spindle is now
disassembling.
Just beneath the plasma membrane, a
band of microfilaments at the former
spindle equator contracts, so that its
diameter shrinks all around the cell.
The contractions
continue and cut
the cell in two.
Fig. 9.7, p. 154