Cell Growth and
Division
Chapter 10
Chromosomes, Mitosis
and Regulation
Why do cells divide?
Purpose?
Is it a set rate of division?
What happens when rate changes?
Limitations to Cell Growth
1. Larger a cell becomes, the more demand on
DNA. Why?
-The larger a cell becomes, the harder it is for a cell’s
DNA to keep up with the entire cell.
-Compare it to a growing town…
-…….Library has enough books for a small town, when it
continues to grow the library can no longer keep up with
the demands of the citizens.
Limitations to Cell Growth
2. Exchanging of materials.
- water, food, oxygen come in the cell.
- wastes leave the cell.
- not always at the same rate because
water, food, oxygen aren’t always used at the
same rate.
- Based on the relationship between the
cell’s volume and surface area.
Division of the Cell
-Cell Division- the process by which a cell divides
into 2 daughter cells.
-Parent Cell- original cell
-Daughter Cells- 2 cells produced after the parent cell
divides.
-Before a cell divides DNA copies or replicates
itself. 1 set of DNA for each daughter cell.
-Cell division solves the problem of a cell getting
too large
Cell Division
2 stages of Cell Division
- Mitosis- Division of the cell nucleus
- Cytokinesis- Division of the cell cytoplasm
Before cell division can occur, chromosomes need
to replicate!
- chromosomes aren’t visible in cell until cell
division.
- at beginning of cell division the chromosomes
become visible contract into dense, visible structures.
Chromosome Continued
• In your notebook draw and label a replicated
chromosome!
• Be sure to label- Chromatids, centromere
• What relationship do we recognize the
chromatids as having?
CELL DIVISION
• The Cell Cycle
– 2 Parts
• Interphase
• Mitosis (Mitotic Phase)
• What parts on the diagram of cell cycle do you
think make up interphase?
– G1, S, G2
Interphase
• Period of time between cell divisions.
• During Interphase the cell will grow, replicate
DNA and prepare for mitosis.
• Longest phase of the cell cycle.
• The three stages are…..
– G1 phase- Growth
– S phase- DNA replication
– G2 phase- prepares for mitosis
Mitosis (Mitotic Phase)
• Stages of Mitosis are divided into 4 phases
– Prophase
– Metaphase
– Anaphase
– Telophase
TO DO: Cell Cycle
• What are the 2 phases of the cell cycle?
• Why do cells need to divide?
• What are the steps (stages) of the cell cycle?
Prophase
• First and longest phase of mitosis
• The chromosomes become visible.
• Chromatin condense and thicken- now called
Chromosomes.
• The nuclear envelop begins to break down.
• Centrioles move to opposite “poles” or ends of the
nucleus.
• The centrioles help to begin to form/organize the
spindle Prophase Picture
Metaphase
• The mitotic spindle (organized by centriole)
fully develops.
• The chromosomes line up at the metaphase
equator ( middle)
• Each chromosome is connected to a spindle
fiber.
• Metaphase Picture
Anaphase
• Sister chromosomes split and begin moving to
opposite ends (poles) of the cell.
• Spindle fibers lengthen and elongate the cell.
• Each pole contains a full compilation of
chromosomes
• The sister chromatids split into individual
chromosomes
• Anaphase Picture
Telophase
• Chromatin begin to form at opposite poles.
– Chromosomes lose their distinct shapes.
• The nuclear envelope and nucleolus also
reappear.
• 2 distinct new nuclear envelops develop.
• Telophase Picture
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Cytokinesis
• The cytoplasm of the original cell’s are split in
half.
• In plant cells a cell plate forms between the 2
new cells.
• In animal cells a cleavage furrow is formed.
Cell Division
• What does it really look like?
• http://www.hybridmedicalanimation.com/ani
m_mitosis.html
10.3- Regulating the Cell Cycle
• Not all cells move through the cell cycle at the
same rate.
– Most muscle and nerve cells don’t divide after
creation.
– Most skin, bone marrow and digestive cells
regulate constantly- go through the cell cycle
every 4 hours.
Controls on Cell Division
• Cells don’t divide when they touch other cells.
• Proved by scientists- grew cells in a petri dish and
they only grew to cover the entire dish.
• When cells in the middle of the dish were removed,
the section grew back so the entire dish was
covered.
• Similar in our bodies- cut on skin, cells closest to it
are stimulated and begin to grow- this is when
healing begins.
Cell Cycle Regulators
• Cyclin- protein found in 1980’s that is only
found in cells that are dividing.
• When cyclin is placed in a non-dividing cell the
cell instantly begins the process of cell
division.
• Internal and External Cell regulators.
Internal Cell Regulators
• Proteins that respond to events inside the
cell
• Allow the cell to only proceed when certain
checkpoints have been met.
– Ex: when ALL chromosomes have been replicated
will cell division begin.
– Ex: All chromosomes must be attached to a
mitotic fiber at the centromere before anaphase
can begin.
External Regulators
• Respond to events outside the cell.
• Speed up or slow down the cell cycle.
• Growth factors are the most important cell
regulators
– Stimulate the growth and division of cells.
– Important during embryo growth or healing.
– Molecules found on the surface of other cells often stop
cells from growing.
Uncontrolled Cell Growth
• So many cell regulators because of the severe
consequences of cell growth.
• Main way we see uncontrolled cell growth is
through Cancer.
• Cancer- when certain body cells lose the ability to
control growth.
• Cancer cells DO NOT respond to the signals that
regulate the growth of most cells.
• Result of growth cells form tumors and tumor
damage surrounding tissue. Severe consequences.
Cancer
• Causes– Smoking tobacco
– Radiation exposure
– Viral Infections
• An extremely high amount of cancer cells contain a
defect in gene p 53. p 53 normally halts cells
division until all chromosomes have replicated.
• Defect in p53 gene does not allow cells to respond
to signals that control their growth.
Cancer types
• See Handout
• Begin discussion on Cancer photostory.
• Serious issue, expect it to be taken as such!