Transcript Ch 10: Cell Growth and Division

Ch 10: Cell Growth and
Division
Cells
 Do not continue to
grow bigger, instead
they produce more
cells
Why is this?
1. The larger a cell becomes, the more
demands the cell places on its DNA
(genetic material).
2. The cell has more trouble moving
enough nutrients and wastes across the
cell membrane.
Cell Division
 growth and repair in
eukaryotes
 one parent cell divides
into 2 new daughter
cells
Cell Division
The parent cell passes on
an exact copy of their
chromosomes (located in
DNA) to their daughter
cells!
What is the cell cycle?
Continuous process where
cells grow, make copies of
their chromosomes, and
divide to form daughter
cells.
Cell Cycle has 3 Phases:
1. Interphase
2. Mitosis
3. Cytokinesis
The cell cycle
1 hour – several days
depending on the type of
cell involved.
Cell Cycle
Interphase
Where most time is spent.
Growth and DNA
replication (copying)
occur
Interphase
 3 stages
 G1
 S phase
 G2
G1 Phase
 Cell grows
 synthesize new
proteins and
organelles
 New cytoplasm
forms
S Phase
Chromosomes
duplicate
G2 Phase
 Growth
continues
 Prepare for
mitosis
Mitosis
 Makes up most of the “M
Phase.”
 Nucleus divides into new
nuclei
 Each nucleus has a complete
set of chromosomes.
Mitosis
4 Phases (PMAT):
 Prophase
 Metaphase
 Anaphase
 Telophase
Prophase
 Chromosomes becomes visible
 Sister chromatids are attached at the
centromere.
 Nuclear membrane breaks down
 Centrioles travel to opposite poles of the cell.
 A fanlike spindle forms around each centriole.
Chromosomes within
Prophase
 carry genetic information
 consists of DNA
 cells have a specific
number of chromosomes
Chromosomes continued…
Humans have 46
chromosomes in each cell
Chromatids
Paired strands of a
duplicated chromosome.
Attached at a centrral
region called the
centromere
Centromere
Chromatid
Metaphase
Chromatids line up across the
center of the cell
Centromeres are attached to a
spindle fiber.
Metaphase
Anaphase
Spindle fibers pull sister
chromatids apart at centromeres to
opposite ends of the cell.
Telophase
 Chromosomes reach opposite poles
of the cell and begin to uncoil.
 Spindle breaks down
 Nuclear membranes reform around
the chromosomes at each pole
 The cell has 2 identical nuclei each
with a complete set of
chromosomes.
Cytokinesis
 Division of cytoplasm into 2
separate cells
 Works different for animal and
plant cells.
Cytokinesis
 Animal Cells = Central groove called a
“cleavage furrow” forms in the plasma
membrane and pinches the 2 daughter
cells apart.
 Plant Cells= Involves the formation of a
cell plate between the nuclei. Cell plate
then transforms part of the cell wall of
each new cell.
Cytokinesis
This process is found in unicellular
eukaryotes and some multicellular
organisms
Use cell division to make
NEW cells
Organisms also use mitosis
to REPLACE cells that are
damaged or no longer
useful to the organism.
For example……
 Your body continuously makes new
skin cells by mitosis to replace skin
cells that are worn out.
Mitosis is….
 Asexual Reproduction = Production of
offspring by a single parent.
 Offspring are then exact copies of their parents.
 Examples: Yeasts and freshwater animals (Hydras)
reproduce this way. Their offspring develop from
buds on the parents body.
Organisms that reproduce
asexually
Cyclin
 protein
 regulates the timing
of the cell cycle in
eukaryotic cells
Regulatory Proteins
 Two types
1.Internal Regulators
2.External Regulators
Internal Regulators
 proteins that respond to
events inside the cell
 signals cell cycle to
continue ONLY WHEN
OTHER THINGS ARE
COMPLETE
External Regulator
 proteins that respond to
events outside the cell
 direct cells to speed up or
slow down the cell cycle
 example: growth regulators
Why is cell growth
regulated so
carefully?
Uncontrolled Cell Growth
 Cancer
 body loses ability to control
growth
 does not respond to the
regulator proteins
 result = large masses of cells
Tumors
masses of cells
 damages the surrounding
tissues
 cells break off and spread
throughout the body
Cause of cancer
 brought on by smoking
tobacco
 radiation exposure
 viral infection
 etc
All cancers have one thing
in common….
The cell cycle has broken
down