Download Superior Cell Cycle

Superior Cell Cycle
Chapter 12 notes
I. Purpose
A. Reproduction
1. Unicellular organisms use the cell
cycle to make offspring
2. Multicellular organisms use the cell
cycle for Growth (1 cell to many),
Repair (after injury) and Renewal
(replacing cells that die from normal
wear and tear)
II. Genome - total amount of a
cell’s DNA
A. prokaryotes - single, circular
strand
B. eukaryotes - DNA packaged into
chromosomes. Each species has a
characteristic number
1. humans somatic (body) cells 46 chromosomes
2. humans gametes (sex) cells 23 chromosomes
III. Vocabulary
A. chromatin - linear strand of DNA
along with proteins that help it
maintain it’s structure and control
activity of genes
III. Vocabulary
B. chromosome - (after DNA
duplicates) -when cell is preparing to
divide - chromatin coils and folds and
becomes thickened
III. Vocabulary
C. sister chromatids - each
strand of the chromosome
contains identical DNA to
the other strand
D. centromere - place
where 2 sister chromatids
are attached
III. Vocabulary
E. mitosis - division of the nucleus of
the cell
F. cytokinesis - division of the
cytoplasm (rest of the cell)
G. meiosis - division to make
gametes (more next chpt)
IV. Cell Cycle for Somatic Cells
A. Interphase - 90% of cell cycle
1. G1 phase - cell grows by
producing proteins and organelles
2. S phase – Synthesis DNA/
chromosomes make exact copy
(replicates)
3. G2 phase - cell grows more and
prepares for division
IV. Cell Cycle for Somatic Cells
B. Mitosis - series of steps to divide
nucleus of cell
1. Prophase
a. chromatin becomes coiled into
chromosomes
b. nucleolus disappear
c. centrosomes (centrioles) move to
opposite poles
d. spindle (made of microtubules) begins
to form
2. Prometaphase
a. nuclear envelope (membrane)
disappears
b. microtubules extend across cell
c. kinetechore (near centromere)
becomes visible
3. Metaphase
a. chromosomes line up on
metaphase plate
b. centromeres aligned with each
other
C. Kinetochores of the sister
chromatids attach to kinetochore
microtubules
4. Anaphase
a. centromeres separate, pulling
sister chromatids apart
b. chromosomes move to opposite
ends of cell as microtubules shorten
c. Cell elongates
d. end with identical chromosomes at
each side
5. Telophase
a. “daughter” nuclei form at each end
of cell
b. nuclear envelopes re-form (from
ER and nuclear fragments)
c. chromosomes uncoil and become
chromatin
d. nucleolus reforms in each new
nucleus
END OF MITOSIS
6. Cytokinesis
a. Animal Cell
1. cytoplasm splits by formation of a
cleavage furrow between cells
2. cells splits in two “daughter cells”
b. Plant cell
1. Vesicles move along center of cell
carrying cell wall materials
2. materials are deposited across the
cell forming a cell plate
V. Binary Fission
1. Cell division (making whole new
organism) for prokaryotic cells
2. Circular DNA replicates, as
membrane pinches, it splits 1
organism into 2
3. Most likely evolved into eukaryotic
mitosis
VI. Cell cycle for plant cells
1. Similar to animals except:
a. spindle forms directly from cell wall
(no centrioles)
b. Cell plate forms instead of
cleavage furrow
Cell Cycle Control System
set of operating molecules that
triggers and coordinates key events in
the cell cycle
*System will proceed on it’s own but
can also be controlled by external and
internal signals
A. Checkpoint
critical control point where stop and
go signals can regulate the cycle
1. Animal cells - have built in
“stop” signals that stop the cycle until
a go-ahead signal comes
a. G1 checkpoint - “restriction point” if it receives a go ahead signal here, it
will continue and divide. If it does not,
it will enter a non dividing state called
G0.
ex. human nerve and muscle cells
are permanently in G0. Liver cells are
usually in G0 unless there is an injury
B. Cell Cycle Control molecules
pace the events of the cycle
1. Protein kinases - enzymes that
activate or inactivate other proteins by
phosphorylating them.
*They are always present in a
growing cell but are “inactive’.
Protein Kinases
*Cyclin - a protein that has a cyclically
fluctuating concentration. This will
activate protein kinases at specific
times.
Cyclin-dependent kinases (Cdk’s)proteins whose activity rises and falls
due to changes in amount of cyclin
*MPF - M-phase promoting factor - Signals
transition from G2 to M (mitosis) phase
-cyclins build up during G-2 and become
associated with Cdk’s.
-this initiates mitosis to begin by
phosphorylating proteins in the nuclear
membrane and stimulating other molecules
-MPF switches itself off by destroying
cyclin using enzymes
C. Internal signals
still under investigation but they know of
one for sure
1. Anaphase will not begin until all
chromosomes are properly lined up
*Signal comes from kinetochores that have
not yet attached
*When all kinetochores are attached, the
wait signal is released and anaphase
begins
D. External signals
1. Growth factor - protein released by
certain body cells that stimulates
others to divide
a. PDGF - platelet derived growth
factor - made by platelets in blood
*PDGF is needed for division of
fibroblasts which are used in blood
clotting
D. External signals
2. Density dependent inhibition of cell
division - crowded cells stop dividing due to amount of growth factors and
nutrients available to each cell
3. Anchorage dependence - In order
to divide, animal cells must be
attached to a substratum (extracellular matrix)
E. Cancer cells
do not respond to body’s control
mechanisms - divide excessively and
invade other tissues
a. Cancer cells do not exhibit density
dependent inhibition - they will continue to
divide even if there is not enough growth
factor
b. Cancer cells (if they do stop) stop at
random points in cell cycle - normal cells in
a lab divide 20-50 times, but they have
cancer cells that have been dividing since
1951
c. Transformation - single cell in a
tissue converts from a normal cell to a
cancer cell. Normally, this is taken
care of by the immune system, but if
the cell somehow avoids destruction,
it can begin dividing
*Tumor - mass of abnormal cells
-benign tumor - mass stays at original
site
-malignant tumor - impairs the
functions of one or more organs =
Cancer
*may have unusual # of
chromosomes
*can lose attachment to tissue and
spread
*can enter blood stream and invade
body = metastasis