Download Chapter 8: The Cell Cycle

CELL CYCLE &
DIVISION
Chapter 10
Cell Cycle
• Series of 4 ordered steps that result in
duplication (copy) of the cell.
When is it done?
• grow, repair, & reproduce!
Cell Cycle
Does this look right?
Cell Cycle
What do you need to
do?
Need a
new cell
Grow
46 Chromosomes
23
46 Chromosomes
23
Repair
S Phase
46
92 Chromosomes
M Phase
46
Phases of Cell Cycle
• G1, S, & G2 are known as
Interphase
– Individual chromosomes are not
visible
• Mitosis: process of sorting &
distributing chromosomes
– Individual chromosomes are
visible with a light microscope
• G0 (Gap or Growth Zero)
– Special stage within G1
– For non-dividing cells or cells that have no
reason to divide & make more of themselves
Special Parts of Cell Cycle
• Restriction or Checkpoints – Point of no return!
What happens if something is wrong
in cell cycle?
• Cells contain proteins that detect mistakes &
damages.
• When a mistake or damage is detected  cell cycle
stops until repairs can be made!
Cell-cycle arrest
If a cell can not be repaired, it will be destroyed!
WHY IS IT IMPORTANT TO DO CELL
CYCLE CORRECTLY?
Cells can not divide or leave a stage of cell cycle until
they are ready & need to do so.
 size

& # of chromosomes could be affected!
Won’t have the complete or correct set of
instructions!
 The
new cells will not function correctly!
 New
cells could be made when they are not
needed or wanted!
• When regulator proteins are inactivated,
cells can grow improperly & out of control
• Uncontrolled cell growth & reproduction =
Cancer
Cancer Progression
•
•
•
There are many different forms of cancer,
affecting different cell types and working in
different ways. All start out with mutations in
specific genes called “oncogenes”. The normal,
unmutated versions of the oncogenes provide the
control mechanisms for the cell. The mutations
are caused by radiation, certain chemicals
(carcinogens), and various random events during
DNA replication.
Once a single cell starts growing uncontrollably, it
forms a tumor, a small mass of cells. No further
progress can occur unless the cancerous mass
gets its own blood supply. “Angiogenesis” is the
process of developing a system of small arteries
and veins to supply the tumor. Most tumors don’t
reach this stage.
A tumor with a blood supply will grow into a large
mass. Eventually some of the cancer cells will
break loose and move through the blood supply
to other parts of the body, where they start to
multiply. This process is called metastasis. It
occurs because the tumor cells lose the proteins
on their surface that hold them to other cells.
Cancer Treatment
• Two basic treatments: surgery to remove the tumor, and
radiation or chemicals to kill actively dividing cells.
• It is hard to remove all the tumor cells. Tumors often lack sharp
boundaries for easy removal, and metastatic tumors can be very
small and anywhere in the body.
• Radiation and chemotherapy are aimed at killing actively dividing
cells, but killing all dividing cells is lethal: you must make new
blood cells, skin cells, etc. So treatment must be carefully
balanced to avoid killing the patient.
• Chemotherapy also has the problem of natural selection within
the tumor. If any of the tumor cells are resistant to the chemical,
they will survive and multiply. The cancer seems to have
disappeared, but it comes back a few years later in a form that is
resistant to chemotherapy. Using multiple drugs can decrease
the risk of relapse: it’s hard for a cell to develop resistance to
several drugs at the same time.
Cell Cycle
Chromosome
Dense rod-shaped
structures made of
DNA & proteins.
Proteins  Histones
Stuff you need to know!
• Chromosome:
– in all living cells
– consists of a single molecule of DNA
– Dyed – specific banding pattern
– carries genes
– Humans have 46 in the form of 23 pairs!
• Sister Chromatids
– 2 connected copies of each chromosome
• Centromere
– center proteins that hold sister chromatids together
Types of Chromosomes
• Autosomes
– Pairs 1 to 22
• Sex Chromosomes
– Pair 23
– Determine the sex of an organism
– X or Y (in humans)
• The two copies of each autosome =
homologous chromosomes
– same size & shape
– Same banding pattern
– Carry genes for the same trait
• Picture of an individuals chromosomes
• Used to
– Test for sex of a baby
– examine & test for genetic disorders
Mitosis
Four distinct steps!
• Prophase
• Metaphase
• Anaphase
• Telophase
Prophase
•
•
•
•
Nucleus membrane breaks down
Chromosomes condense & become visible
Centrioles move to opposite sides of cell
Spindle Fibers begin to form
Metaphase
• Chromosomes line up in the middle of the
cell  metaphase plate
Anaphase
• Spindle fibers contract & pull sister
chromatids to opposite poles
• Sister chromotids separate
– Now considered a single chromosome.
Telophase
• Chromosomes expand & begin to disappear.
• Nuclear envelop reforms for each new cell.
– Produces 2 new nuclei
• Cytoplasm divides cells into two!
– Called Cytokinesis
Summary