Download Mitosis notes 9.03

Mitosis stages
1.
Cell division is necessary for growth and repair of multicellular organisms,
and for reproduction of all organisms.
2.
When not undergoing cell division, a cell’s DNA is a tangled mass of thin
threads called chromatin.
3.
At cell division, long threads of DNA and protein called chromatin coils,
loops, and condenses into highly compact structures called chromosomes.
4.
Each organism usually has a characteristic number of chromosomes: humans
(46), corn (20), crayfish (200), etc.
5.
The full number of paired chromosomes, found in regular body cells, is called
the diploid number.
6.
Half the diploid number, or one chromosome from each pair, is found in the
sperm or egg of animals and is called the haploid number.
7.
Cell division of eukaryotes involves both nuclear division and cytokinesis
(division of the cytoplasm)
8.
Prior to cell division, each chromosome duplicates to form two identical parts
called sister chromatids attached to each other at a region called the
centromere.
9.
Division of centromeres releases two daughter chromosomes, one for each
daughter cell.
10.
What is in a chromosome?
a. Eukaryotic chromosome is over 50% protein
b. Some proteins are involved in DNA and RNA synthesis
c. Large proportion of protein are histones
d. Histones package over two meters of DNA molecules in small space.
e. DNA double helix is wound around core of eight histones forming a bead
called a nucleosome (repeating units of chromatin structure, each
consisting of a length of DNA wound around a complex of eight histone
molecules. Adjacent nucleosomes are connected by a DNA linker
associated with another histone protein.
11.
The Cell Cycle
a. Before 1950’s, lack of chromosomal activity between cell divisions led
scientists to consider this a resting state termed interphase
b. Interphase is now known to include DNA replication, changing
perspective to an ongoing cell cycle concept.
c. The M stage is the entire cell division stage, including both mitosis and
cytokinesis
d. The S stage is the period of DNA synthesis when replication occurs; the
chromosomal proteins are also synthesized at this stage.
e. The G1 stage (“G” for “gap”) prior to S stage is a time the cell grows in
size
f. The G2 stage prior to M stage involves metabolic events preparing for
mitosis
12.
Cell Cycle Control
a. some cells such as skin cells divide continuously
b. Skeletal muscle cells and nerve cells are arrested in the G1 stage
c. Experiments fusing cells at different stages reveal two critical
checkpoints:
G1 stage  S stage
G2 stage  M Stage
d. Activation of kinase, enzyme that removes a phosphate group from ATP,
is a method to turn on various metabolic pathways and regulate the cell
cycle.
e. Cyclin is a protein that activates kinases, but is destroyed by resultant
enzymes.
f. The cell cycle is ultimately controlled by these cyclin-dependent kinase
interactions.
g. Cyclins that have gone awry are one reason for cancer tumors.
Mitosis in Detail
1.
Mitosis is nuclear division that produces two daughter nuclei with the same
chromosomes as the parent nucleus.
2.
Before mitosis, a spindle forms to bring about an orderly distribution of
chromosomes to the daughter nuclei; the spindle consists of fibers made from
microtubules.
3.
Tubulin protein dimers join and split to assemble and disassemble the
microtubules.
4.
Animal cells contain organizing centrosomes made in a pair of centrioles
made of microtubules; plant cells lack centrioles.
5.
Animal cell mitosis involves no cell wall, has centrioles present in the
centrosomes, and a cleavage furrow forms to divide cells.
6.
Stages of Mitosis (PMAT)
a. Prophase
i. Centrosomes move toward opposing ends
ii.
Spindle fibers appear
iii.
Nuclear envelope fragments
iv.
Nucleolus disappears
v.
Chromosomes are visible
b. Prometaphase
i. Spindle develops poles, asters, and fibers
ii.
Centromeres of chromosomes attach to spindle fibers
without orientation
c. Metaphase
i. Chromosomes attached to centromeric spindle fibers are aligned at the
metaphase plate or equator of spindle.
ii.
7.
8.
At close of metaphase, centromers uniting sister chromatids
split
d. Anaphase
i. Daughter chromosomes move to the opposite poles
ii.
Dyenin, present in microtubules in flagella, is likely motor
molecule in centromeres.
iii.
Spindle lengthens, extending distance between poles
e. Telophase
i. Spindle disappears, chromosomes arrive at the poles
ii.
The spindle apparatus disappears as microtubules
disassemble
iii.
New nuclear envelope forms around daughter
chromosomes
iv.
Chromosomes diffuse into chromatin
v.
Nucleolus appears in each daughter nucleus.
Cytokinesis (cytoplasmic division)
a. in animal cells, a cleavage furrow forms (indentation of cell membrane) as
anaphase draws to a close
b. Actin filaments form a contractile ring; as the ring gets smaller, the
cleavage furrow pinches the cell and form two daughter cells
Plant mitosis, occurs primarily in meristematic tissue at tips of roots and stems
and edge of trunk; has same stages as animal mitosis with two main
differences:
a. plants lack centrioles and asters; however, spindle fibers and centrosomes
are present.
b. Rigid cell wall does not permit furrowing; instead, a cell plate is formed
by Golgi-produced vesicles that fuse at equator; cellulose fibrils are added
for strength later.
Mitosis
Mitosis is the process by which the nucleus of most eukaryotic cells divides. Mitosis as
four phases: prophase, metaphase, anaphase, and telophase.
Color each chromosome in prophase a different color. Follow each of these
chromosomes through mitosis. Show this by coloring the correct structures in each
phase of mitosis