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Ch 10 and 11.4
CELL GROWTH AND DIVISION
10.1 Notes
CELL GROWTH, DIVISION, AND
REPRODUCTION
Answer the first question
 List some of the difficulties you think a cell
faces as it increases in size?
Two main reasons why cells divide rather than
grow larger…
1.
The larger a cell becomes, the more demands the
cell places on its DNA.
 As a cell increases in size its DNA does not.
 A larger cell would make a greater demand on its
genetic “library”.
Two main reasons why cells divide rather than
grow larger…
2. A larger cell is less efficient in moving nutrients and
waste materials across the cell membrane.
 The rate at which materials are exchanged across the
cell membrane depends on the surface area of the
cell.
Two main reasons why cells divide rather than
grow larger…
 The rate at which food and oxygen are used up and
waste products are produced depends on the cells
volume.
 The cell works best when there is a larger surface
area than volume.
Division of the cell
 The process by which a cell divides into two new
daughter cells is called CELL division.
 Before cell division occurs the cell replicates all of its
DNA. Each daughter cell will get a complete copy of
the DNA.
Asexual Reproduction
 The production of genetically identical offspring
from a single parent is known as asexual
reproduction.
 Breaking down the term a = not and sexual =
needing two members
Asexual Reproduction
occurs in many single-celled
organisms, and in some multicelled organisms.
 Ex: single-celled bacterium
 Ex: multi-celled hydra

Where each new bud will eventually
break off to form its own individual
organism.
Sexual Reproduction
 Sexual Reproduction involves the fusion of two
separate parent cells. Offspring will inherit some of
their genetic information from each parent.
 This process creates genetic diversity.
Comparing Asexual and Sexual Reproduction
 For single-celled organisms, asexual reproduction is
a survival strategy. When conditions are right , the
faster they reproduce, the better their chance of
survival over other organisms using the same
resources.
~ There is a lack of genetic diversity which can
become a disadvantage when conditions change in
ways that do not fit the characteristics of an
organism.
Comparing Asexual and Sexual Reproduction
 Sexual reproduction is good in that it creates genetic
diversity and the slow growth of offspring allows for
better survival when there are changes in
environment and food availability.
Comparing Asexual and Sexual Reproduction
 Some organisms make use of both types of
reproduction. Ex: Yeast is a single-celled eukaryote
that produces asexually most of the time however
under the correct conditions may enter a sexual
phase.
10.2 Notes
THE PROCESS OF CELL DIVISION
Chromosomes
 Chromosomes are genetic information that has
been bundled into packages. This is important
for space saving.
Ex: the bacterium E. coli’s DNA molecule is 1.6mm
which is 1000 times longer than the E. coli itself!
This is why bundling into a package helps a ton.
Chromosomes
Prokaryotic Chromosomes
 Lack a defined nucleus and many other organelles
 Contain only a single, circular DNA chromosome
that contains all, or nearly all, of the cell’s genetic
information.
Eukaryotic Chromosom
 Tend to have much more DNA than prokaryotes and
therefore contain multiple chromosomes.
Ex: Fruit flies 8 chromosomes per cell
Ex: Humans 46 chromosomes per cell
Ex: Carrots 18 chromosomes per cell
Eukaryotic Chromosomes
 Chromosomes work closely with the protein histone
in order to form chromatin. DNA tightly coils
around the histones in order to form bead-like
structures called nucleosomes.
 Usually the chromosome shape you always see is a
duplicated chromosome with supercoiled chromatin.
The Cell Cycle
 During the cell cycle, a cell grows, prepares for
division, and divides to form two daughter cells.
Each daughter cell will then go through this
process.
The Prokaryotic Cell Cycle
 Begin to replicate their DNA chromosomes once they
have grown to a certain size.
Prokaryotic Cell Cycle
 When replication is complete they begin to divide.
 Division in prokaryotes is asexual reproduction
known as binary fission.
 Two DNA’s go to different sides of the cell and attach
Prokaryotic Cell Cycle
 Fibers form between them and constrict pinching the
cell inwards dividing the cytoplasm and
chromosomes between two newly formed cells.
 Forms two genetically identical cells.
Eukaryotic Cell Cycle
 Consists of four phases:
G1, S, G2, and M
 The length of each phase
depends on the type of
cell. The G in G1 and G2
stands for gap though
these are periods of
intense activity.
Eukaryotic Cell Cycle
G1 Phase: Cell Growth
 Cells increase in size
 Synthesize new proteins
and organelles.
Eukaryotic Cell Cycle
S Phase: DNA Replication
 The S stands for synthesis
because during this phase
new DNA is synthesized
when the chromosomes are
replicated.
 The cell at the end of S
phase contain twice as much
DNA as it did at the
beginning.
Eukaryotic Cell Cycle
G2 Phase: Preparing for
Cell Division
 Usually the shortest of the
three phases of interphase.
 Many of the organelles and
molecules required for cell
division are produced.
Eukaryotic Cell Cycle
M Phase: Cell Division
 Occurs following interphase
and produces two daughter
cells.
 Gets its name from the
process of mitosis.
Eukaryotic Cell Cycle
M Phase: Cell Division
 While interphase can be
quite long, the process of
cell division usually takes
place quickly.
 Two main stages: mitosis
then cytokinesis
Mitosis
 Four stages: prophase,
metaphase, anaphase,
and telophase
Prophase
 Longest stage usually
taking up half the time of
mitosis.
 The genetic material
inside the nucleus
condenses and the
duplicated chromosomes
become visible.
Prophase
 Outside the nucleus, a
spindle starts to form.
These are microtubules
that are extending from
centrioles.
 The centrioles, which
were duplicated during
interphase move towards
opposite ends (poles), of
the cells.
Prophase
 As prophase ends, the
chromosomes coil more
tightly, the nucleolus
disappears, and the
nuclear envelope breaks
down.
Metaphase
 The shortest of the four
phases.
 During metaphase, the
centromeres of the duplicated
chromosomes line up across
the center of the cell.
 Spindle fibers connect the
centromere of each
chromosome to the two poles.
Anaphase
 Anaphase begins when
the duplicated
chromosome (sister
chromatids) suddenly
separate into individual
chromosomes and begin
to move apart to
different poles.
Anaphase
 Anaphase comes to an
end when this movement
stops and the individual
chromosomes are
completely separated
into two groups.
Telophase
 During telophase, the
chromosomes, which
were distinct and
condensed, begin to
spread out in a tangle of
chromatin.
Telophase
 A nuclear envelope
reforms around each
cluster of chromosomes.
 Spindles begin to break
apart.
Telophase
 Nucleolus becomes
visible in each daughter
nucleus.
 Mitosis is now complete.
There is still one step of
cell division left to go.
Cytokinesis
Animal
Plant
 The cell membrane is
 Because the cell
drawn inwards until the
cytoplasm is pinched in
nearly two equal parts
each containing their
own nucleus and
cytoplasmic organelles.
membrane is not flexible
enough to draw inward
due to the cell wall a
structure known as a cell
plate forms halfway
through the cell to divide
nuclei. The cell plate will
eventually become a cell
membrane and then a
cell wall.
10.3
REGULATING CELL GROWTH
Controls on Cell Division
 3 types of controls
 Cyclins
 Regulatory
 Apoptosis
Proteins
Cyclins
 In the early 1980’s biologists discovered a protein
that when injected into cells could cause spindles to
form it was called cyclin. This protein is found in
cells that were undergoing mitosis.
 Called cyclin because it seems to regulate the cell
cycle. Since its discovery a whole family of cyclins
have been discovered that control the timing of the
cell cycle in eukaryotic cells.
Regulatory Proteins
 Scientists have since discovered dozens of other
proteins that help to regulate the cell cycle.
 There are internal regulators that allow the cell cycle
to proceed only when certain events have occurred
inside the cell(ex: chromosome duplication, spindle
fibers formed)
Regulatory Proteins
There are also external regulators respond to events
outside of the cell and direct cells to either speed up
or slow down the cycle.
 Ex: Growth factors that stimulate the growth and
division of cells. Very important during embryonic
development and wound healing.
 Other proteins will slow the cell cycle to keep too
much growth from occurring.
Apoptosis
 Cells die in one of two ways: damage/injury or
apoptosis.
Apoptosis
 Apoptosis is the programmed cell death where the
cell will go through a series of controlled steps
leading to its self-destruction.



Cell and chromatin shrink
Parts of the cell membrane break off.
Neighboring cells then quickly clean up the cell’s remains.
 A balance of cell growth/death must occur to keep an
organism healthy.
Cancer: Uncontrolled Cell Growth
How do cancer cells differ from other cells?
 Cancer is a disorder in which body cells lose the
ability to control growth.
 Cancer cells do not respond to the signals that
regulate the growth of most cells. As a result cells
will divide uncontrollably.
Cancer: Uncontrolled Cell Growth
 Cancer cells form a mass called a tumor. Some are
benign or non-cancerous. However there are others
that are malignant or cancerous. These will spread
to invade and destroy surrounding healthy tissue.
These will absorb nutrients needed for other cells.
What causes cancer?
 Defects in the genes (parts of DNA) that regulate cell
growth and division.
 Examples of sources of defects: smoking or chewing
tobacco, radiation exposure, other defective genes,
and even viral infections.
 If a cancer cell can spread into the blood stream then
it can effectively move into other parts of the body…
this is very bad.
Treatments for cancer
Surgery
 If a tumor is localized, and spotted early enough, it
can be treated this way. Ex: skin cancer.
Treatments for cancer
Radiation
 If a tumor is growing too fast for surgery then
carefully targeted beams of radiation can be used to
help.
Treatments for cancer
Chemical compounds (Chemotherapy)
 With these compounds one can possible kill cancer
cells, or at least slow their growth.
 However it also kills non-cancerous cells which
causes serious side effects in patients.
 Much more work is needed to understand the full
cell cycle in order to see what is truly happening in
cell division.
11.4
MEIOSIS
Intro to Meiosis
 Mitosis is the asexual reproduction of somatic
cells (body cells). Forms two identical daughter
cells with the same chromosome count as the
original (diploid).
Ex: skin cells, muscle cells
Intro to Meiosis
Meiosis is the first stage in sexual reproduction.
Forms four genetically different cells called
gametes. Each daughter cell has half the DNA of
the original (haploid).
 Ex: Sex cells.
Female egg formed in the ovaries.
Male sperm formed in the testes.
Sex Cells (gametes)
Eggs (oogenesis)
 Although meiosis creates four haploid daughter cells
only one female cell is larger than the others. The
other three smaller polar bodies do not survive.
Sperm (spermatogenesis)
 Unlike eggs there will be four usable sperm out of a
run of meiosis.
Sexual Reproduction
 Meiosis forms gametes which have 23
chromosomes each.
 One gamete from the female (egg) and one
gamete from the male (sperm) will combine
(fertilization) to form a zygote with 46
chromosomes.
Mitosis vs. Meiosis: Which is it?
 Formation of sex/gamete cells
_________________________
 Formation of body/somatic
cells________________________
 The process by which an embryo forms into a
baby _____________________
Mitosis vs. Meiosis: Which is it?
 Formation of sex/gamete cells MEIOSIS
 Formation of body/somatic cells MITOSIS
 The process by which an embryo forms into a
baby MITOSIS
Haploid (N) vs. Diploid (2N)
 The process of meiosis cuts the chromosome
count in half.
 If an organism starts with 20 chromosomes what
will their daughter cells have after a full run of
meiosis? ______
 If an organism has 15 chromosomes in each
daughter cell how many must it have started with
at the beginning of meiosis? _____________
Haploid (N) vs. Diploid (2N)
 The process of meiosis cuts the chromosome
count in half.
 If an organism starts with 20 chromosomes what
will their daughter cells have after a full run of
meiosis? 10
 If an organism has 15 chromosomes in each
daughter cell how many must it have started with
at the beginning of meiosis? 30
Crossing Over
 During prophase 1 the cells form tetrads where
the chromosomes will pair up. During this time
the chromosomes can intertwine with each other
going through crossing over. They will then
exchange genetic information.
Crossing Over
 Due to all the different alleles
that can exchange there are 8.4
million individual sperm or egg
combinations that can result,
and when there is fertilization
there is 8.4 mill. x 8.4 mill. =
70.6 trillion different types of
children that can occur. Yay for
genetic diversity. 
Fraternal vs. Identical Twins
 Fraternal: When a female ovulates two eggs
instead of one and both become fertilized.
 Identical: When a female ovulates one egg and
after fertilization that one egg splits giving both
identical DNA.
Karyotypes
 Picture of a person’s
chromosomes all lined
up.
(23 from mom and 23 from
dad)
Downs Syndrome
 When there is an extra
chromosome 21 also
called Trisomy 21.
 The child then has 47
instead of 46
chromosomes.
Turners Syndrome
 Female only has one X
chromosome where
they are now
monosomy or one less
giving them 45 instead
of 46.