Ch. 9 Cellular Reproduction
I.
Cellular Growth
Main Idea: Cells grow until they reach their size limit, then they
either stop growing or divide.
A. Cell Size Limitations
1. ratio of surface area to volume is the main limiting
factor for the size of a cell
a. as the cell grows, volume increases much
more rapidly than the surface area
b. if cell becomes too large, the cell has
problems supplying nutrients and expelling
wastes
c. transporting substances becomes inefficient
using diffusion or the cytoskeleton if the cell
becomes too large; small cells have much
more efficient transport systems
d. cellular communication is more difficult in
large cells b/c signals involve the movement
of substances.
B. The Cell Cycle: the process in which a cell grows and divides
becoming 2 cells.
C. Stages of cell cycle:
1. Interphase: cell grows, carries out cellular functions,
and makes copies of its DNA (replication) in
preparation for the next stage
a. G1 (Gap 1): cell grows and performs normal
functions
b. S: synthesis (DNA is replicated)
c. G2 (Gap 2): cell prepares for mitosis
2. Mitosis: cell’s nucleus and nuclear material divide
a. divided into 4 substages
3. Cytokinesis: method by which the cell’s cytoplasm
divides, creating a new cell.
D. cell cycle duration: most animal cells take 12-24 hr.
E. stages of interphase:
1. G1: period immediately after cell division; cell grows,
carries out normal activities and prepares to replicate
DNA
2. S: cell copies its DNA in preparation for division
 Chromosomes: contain genetic material
 Chromatin: relaxed form of DNA in the
cell’s nucleus that condense to form
chromosomes
3. G2: cell prepares for division, synthesizes protein to
make microtubules used for division and takes
inventory
II.
Mitosis and Cytokinesis
main idea: eukaryotic cells reproduce by mitosis, the process of
nuclear division, and cytokinesis, the process of cytoplasm
division.
A. Mitosis
1. most important part is the accurate separation of the
cell’s replicated DNA to pass the cell’s genetic
information into the new cells.
2. increases the number of cells in a growing organism
and replaces damaged cells
Important Terms
o Chromosomes: Organized structures that
contain DNA
o Chromatin: Thin fibers of DNA and protein
molecules
o Sister Chromatids: The two halves of a
chromosome which contain identical genes
o Centromere: The region of the chromosome
where the sister chromatids are joined
together
B. The Stages of Mitosis
1. prophase
 longest stage
 chromatin condenses into chromosomes (x-shaped)
sister chromatids: each half of the paired
chromosome that contain identical genetic material
centromere: structure that attaches sister
chromatids and ensures a complete DNA copy is
passed to the daughter cells
o nucleolus disappears
o spindle apparatus forms: spindle fibers, centrioles
and aster fibers (animal cells only) move and
organize chromosomes before division
o nuclear envelope disappears
o spindle fibers attach to the sister chromatids of
each chromosome on both sides of the centromere
then attach to opposite pole of cell
2. Metaphase
o Sister chromatids are pulled by motor proteins
along spindle apparatus to the equator (middle)
of cell
o Ensures new cells have accurate copies of the
chromosomes
3. Anaphase
 Chromatids are pulled apart
 Microtubules of the spindle apparatus shorten
and pull at the centromeres, causing the sister
chromatids to separate
 Microtubules with the help of motor proteins
move the chromosomes toward the poles of the
cell
4. Telophase
 Chromosomes arrive at the poles of the cell and
begin to decondense
 Two new nuclear membranes begin to form and
the nucleoli reappear
 Spindle apparatus disassembles/ some
microtubules recycled to build cytoskeleton
C. Cytokinesis: process that divides the cytoplasm after mitosis
1. in animal cells, microfilaments pinch the cytoplasm in
two
2. in plant cells, a cell plate forms between the two
daughter nuclei, and cell walls form on either side of
the cell plate
III.
Cell Cycle Regulation
Main idea: the normal cell cycle is regulated by cyclin proteins
A. Normal Cell Cycle
1. cell cycle in eukaryotes is driven by the proteins cyclins
that bind to enzymes called cyclin-dependent kinases
(CDKs).
a. different cyclin-cdk combinations control
different activities at different stages
b. cyclin-cdk combination signals the
beginning of the cell cycle while other
combinations control DNA replication,
protein synthesis, and nuclear division
c. checkpoints in the cell cycle monitor the
cycle and can stop it if something goes
wrong. Ex: check for DNA damage at end of
G1 before the S phase
 G1 Checkpoint
 Cell size
 Suitable environment
 G2 Checkpoint
 Cell big enough
 DNA replicated correctly
 Suitable environment
 M Checkpoint
 All chromosomes are attached
to the spindle
 Problems with the cell cycle control system lead to
cancer.
B. Abnormal Cell Cycle: Cancer
1. cancer: uncontrolled growth and division of cells
(failure in the regulation of the cell cycle)
a. cancer cells spend less time in interphase
than normal cells
2. causes: mutations or changes in the segments of DNA
that control the production of proteins
3. damage is often fixed by repair systems but if repair
systems fail, cancer can result
4. carcinogens: substances that are known to cause cancer
(ex: asbestos, tobacco, radiation)
5. more than one change in DNA is required to turn a
normal cell into a cancer cell so cancer is more likely
with increased age and can be inherited.
6. Tumor: an abnormal mass of cells
a. Benign tumor: abnormal mass of
normal cells; does not change locations
b. Malignant tumor: abnormal mass of
cancerous cells; can move to other
parts of the bodymetastasis.
7. 4 Types of Cancer
a. Carcinomas: cancers that originate in
the external or internal linings of the
body (Ex: skin; lining of intestine)
b. Sarcomas: cancers that originate in
tissues that support the body (Ex:
bone, muscle, fat)
c. Leukemias & lymphomas: cancers
that arise in blood-forming tissues (Ex:
bone marrow; spleen; lymph nodes)
8. Treatments
a. Radiation: Cells are exposed to highenergy radiation, which disrupts the
cell cycle.
b. Chemotherapy: Drugs are used to
disrupt the cell cycle
c. Many work by interfering with the
spindle.
C. Apoptosis: programmed cell death
1. all animal cells appear to have a “death
program” that can be activated (ex: webbing b/w
fingers and toes that disappears at birth, trees
losing leaves during autumn)
2. also occurs in cells damaged beyond repair,
including those with DNA damage; this protects
organism from developing cancerous growths.
D. Stem Cells: unspecialized cells that can develop into
specialized cells (muscle, blood, nerve, bone) under the
right conditions. These can be used to treat many
diseases and conditions.
1. embryonic stem cells: unspecialized cells that
come from embryos early in their development.
2. adult stem cells: found in various tissues and are
used to maintain and repair the same kind of
tissue