Chapter 10 Cell Growth and Division
Bellringer (on PP 227)
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Why do cells need to reproduce?
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Cells need to reproduce so that an organism can function
efficiently (remember the surface area to volume ratio
limitations for cell size) and replace damaged tissue
(eukaryotes only)
Bellringer on PP 178

At what point is a cell committed to division?

After S phase of interphase. Once DNA is
replicated the cell MUST divide or die.
Bellringer on PP 205
 Name
the states of condensation of DNA
in order from least condensed to most
condensed. Why is this important for cell
division?
 Chromatin, nucleosome, chromatid,
chromosome. This is necessary so that
during division, the DNA does not get
tangled and damaged

REPRODUCTION- Because larger cells are more
difficult to maintain, cells divide when they grow to a
certain size. The size of an organism does not increase by
increasing cell size but by increasing the number of cells.
REPRODUCTION
New cells are needed to help tissues and organs grow.
New cells also replace damaged cells. As old cells die and
new cells take their place.
REPRODUCTION
A cell’s ability to exchange substances is limited by its
surface area–to-volume ratio. As a cell gets larger,
substances must travel farther to reach where they are
needed.
REPRODUCTION
The work of cells is done by proteins. As a cell gets larger,
more proteins are required to maintain its function.
REPRODUCTION
If the cell gets too large, DNA instructions cannot be
copied quickly enough to make the proteins that the cell
needs to support itself.
CHROMOSOMES 

CHROMOSOMES -chromosomes are the condensed
DNA of the cell. The way DNA is stored and read differs
between eukaryotes and prokaryotes.
Diagram of winding with histones from book
CHROMOSOMES 

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PROKARYOTES- Prokaryotic chromosomes also have
genes which code for proteins and RNA for the
prokaryotic cell functions.
A prokaryotic cell has a single circular molecule of DNA.
This loop of DNA contains thousands of genes.
A prokaryotic chromosome is condensed through
repeated twisting or winding, like a rubber band twisted
many times.
PROKARYOTES
CHROMOSOMES 
EUKARYOTES- Eukaryotic DNA is packaged into highly
condensed chromosome structures to fit in the nucleus
with the help of many proteins.
CHROMOSOMES 


The large molecule of DNA is organized into hereditary
units called genes. A gene is a segment of DNA that
codes for the RNA and proteins of a particular trait (ex
hair color).
The DNA and proteins make up a substance called
chromatin.
The first level of packaging is done by a class of proteins
called histones. A group of eight histones come together
to form a disc-shaped histone core.
DNA COILING AROUND HISTONES
CHROMOSOMES 


The long DNA molecule is wound around a series of
histone cores in a regular manner and is called a
nucleosome.
The string of nucleosomes lines up in a spiral to form a
cord that is 30 nm in diameter.
During most of a cell’s life, its chromosomes exist as
nucleosomes.
CHROMOSOMES 

As the cell prepares to divide, the chromosomes
condense even further ensuring that the extremely long
DNA molecules do not get tangled up during cell division.
The nucleosome cord forms loops then coil into the final,
most highly condensed form of the chromosome.
CHROMOSOMES 


Each of the two thick strands of a fully condensed,
duplicated chromosome is called a chromatid.
Each chromatid is made of a single, long molecule of
DNA.
Identical pairs, called sister chromatids, are held together
at a region called the centromere.
CHROMOSOMES 

During cell division, the sister chromatids are separated
at the centromere, and one ends up in each daughter cell.
Each new cell has the same genetic information as the
parent cell.
PREPARING FOR CELL DIVISION
PREPARING FOR CELL DIVISION- The process of
cell division involves more than cutting a cell into two
pieces. Each new cell must have all of the equipment
needed to stay alive. Each new cell will function in the
same way as the cells that they replace.
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ps/hx8_crp_cm.htm
PREPARING FOR CELL DIVISION


Prokaryotes-prokaryotic cell division is more simple than
eukaryotic division
In prokaryotic cells, the circular DNA molecule is
attached to the inner cell membrane.
The cytoplasm is divided when a new cell membrane
forms between the two DNA copies. Meanwhile the cell
continues to grow until it nearly doubles in size.
PREPARING FOR CELL DIVISION

The cell is constricted in the middle, like a long balloon
being squeezed near the center.
Eventually the dividing prokaryote is pinched into two
independent daughter cells, each of which has its own
circular DNA molecule.
PREPARING FOR CELL DIVISION


Eukaryotes
Eukaryotic cells have many organelles. In order to form
two living cells, each daughter cell must contain enough of
each organelle to carry out its functions.
The DNA within the nucleus must also be copied, sorted,
and separated.
EUKARYOTIC CELL CYCLE 
EUKARYOTIC CELL CYCLE -The life of a eukaryotic
cell cycles through phases of growth, DNA replication,
preparation for cell division, and division of the nucleus
and cytoplasm. The cell cycle is a repeating sequence of
cellular growth and division during the life of a cell. The
cell cycle is made up of five phases. The first three phases
together are known as interphase. The remaining two
phases make up cell division.
EUKARYOTIC CELL CYCLE INTERPHASE

G1- During the first gap
phase (G1), a cell grows
rapidly as it builds more
organelles. For most
organisms, this phase
occupies the major
portion of the cell’s life.
EUKARYOTIC CELL CYCLE INTERPHASE

S-During the synthesis
phase (S), a cell’s DNA is
copied. At the end of the S
phase, the cell’s nucleus
has twice as much DNA
as it did in the G1 phase.
EUKARYOTIC CELL CYCLE INTERPHASE

G2-During the second gap
phase (G2), the cell
continues to grow and
prepares to divide. Hollow
protein fibers called
microtubules are
organized in the
cytoplasm during G2.
EUKARYOTIC CELL CYCLE - MITOSIS


STAGES OF
MITOSIS - Mitosis is a
continuous process that
can be observed in four
stages: prophase,
metaphase, anaphase, and
telophase.
EUKARYOTIC - MITOSIS- PROPHASE



Stage 1: Prophase
Within the nucleus, chromosomes begin to condense
The nuclear membrane breaks down. Outside the
nucleus, a special structure called the spindle forms. The
spindle is made up of several spindle fibers.
EUKARYOTIC - MITOSIS- PROPHASE


Stage 1: Prophase
The nuclear membrane breaks down. Outside the
nucleus, a special structure called the spindle forms. The
spindle is made up of several spindle fibers.
EUKARYOTIC - MITOSIS- PROPHASE

Cells have an organelle called the centrosome, which
helps assemble the spindle
EUKARYOTIC - MITOSIS- PROPHASE


In animal cells, the centrosome includes a pair of
centrioles.
Before mitosis, the cell’s centrosome is duplicated. During
prophase, the centrosomes move to opposite poles of the
cell.
EUKARYOTIC - MITOSIS- METAPHASE


Stage 2: Metaphase
During metaphase, the
chromosomes are
packaged into their most
condensed form.
EUKARYOTIC - MITOSIS- METAPHASE

The nuclear membrane is fully dissolved, and the
condensed chromosomes move to the center of the cell
and line up along the cell’s equator.
EUKARYOTIC - MITOSIS- METAPHASE

Spindle fibers form a link between the poles and the
centromere of each chromosome.
EUKARYOTIC - MITOSIS- ANAPHASE


Stage 3: Anaphase
Once all of the
chromosomes are lined
up, the spindle fibers
shorten. The spindle fibers
shorten by breaking down
the microtubules bit by bit
EUKARYOTIC - MITOSIS- ANAPHASE

Sister chromatids move
toward opposite poles as
the spindle fibers that are
attached continue to
shorten. Each pole now
has a full set of
chromosomes.
EUKARYOTIC - MITOSIS- TELOPHASE


Stage 4:Telophase
A nuclear envelope forms
around the chromosomes
at each pole of the cell.
EUKARYOTIC - MITOSIS- TELOPHASE

Chromosomes, now at
opposite poles, uncoil and
change back to their
original chromatin form.
EUKARYOTIC - MITOSIS- TELOPHASE

The spindle dissolves and
the spindle fibers break
down and disappear
EUKARYOTIC - MITOSIS- TELOPHASE

Mitosis is complete.
EUKARYOTIC - CYTOKINESIS

CYTOKINESIS-During cytokinesis, the cell membrane
grows into the center of the cell and divides it into two
daughter cells of equal size. Each daughter cell has about
half of the parent’s cytoplasm and organelles. As mitosis
ends, cytokinesis begins. The end result of mitosis and
cytokinesis is two genetically identical cells in place of the
original cell.
EUKARYOTIC - CYTOKINESIS
Separating the Cytoplasm
 In animal cells and other cells that lack cell walls, the cell
is pinched in half by a belt of protein threads.
 In plant cells and other cells that have rigid cell walls, the
cytoplasm is divided by a cell plate.
CONTROLS
CONTROLS-Cell
growth and division
depend on protein signals
and other environmental
signals. Cell division is
highly controlled. Signals
from surrounding cells or
even from other organs
can also regulate cell
growth and division.
Environmental conditions,
such as availability of
nutrients, the amount of
light and temperature, also
affect the cell cycle.
CHECKPOINTS 
CHECKPOINTS -Feedback signals at key checkpoints
in the cell cycle can delay or trigger the next phase of the
cell cycle. During the cell cycle, a cell undergoes an
inspection process to ensure that the cell is ready for the
next phase in the cell cycle.There are three main
checkpoints in the cell cycle—G1checkpoint, G2
checkpoint, mitosis checkpoint.
CHECKPOINTS 
G1 checkpoint- Before the cell copies its DNA, the cell
checks its surroundings. If conditions are favorable and
the cell is healthy and large enough, the cell enters the
synthesis phase. If conditions are not favorable, the cell
goes into a resting period. Certain cells, such as some
nerve and muscle cells, remain in this resting period
forever
CHECKPOINTS 
G2 checkpoint- Before mitosis begins, the cell checks
for any mistakes in the copied DNA. Enzymes correct any
mistakes. This checkpoint ensures that the DNA of the
daughter cells will be identical to the DNA of the original
cell. If the cell passes the G2 checkpoint, then the cell
may begin to divide. Once past this checkpoint, proteins
help to trigger mitosis.
CHECKPOINTS 
Mitosis checkpoint- During the metaphase stage of
mitosis, chromosomes line up at the equator. At this point,
the cell checks that the chromosomes are properly
attached to the spindle fibers. Without this checkpoint,
the sister chromatids may not separate properly giving
one daughter cell too many genes and one not enough
CANCER

CANCER-cancer is uncontrolled cell growth and
division that can result in masses of cells that invade and
destroy healthy tissues. Cancer cell reproduction
continues without the normal feedbacks. The defective
cell divides and produces more defective cells. Eventually,
these cells form a mass called a tumor.
CANCER- DEVELOPMENT



A benign tumor does not spread to other parts of the
body and can often be removed by surgery.
A malignant tumor invades and destroys nearby healthy
tissues and organs.
Malignant tumors, or cancers, can break loose from their
tissue of origin and grow throughout the body. This
process is called metastasis. Once a cancer has
metastasized, it becomes difficult to treat.
CANCER- TREATMENT
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


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Treatment
Some cancers can be treated by using drugs that kill the
fast-growing cancer cells.
Because drugs are chemicals, this method of treatment is
called chemotherapy, or “chemo” for short.
Some cancers can be treated by surgery to remove of the
affected organ.
In radiation therapy, high-energy rays are focused on an
area in order to destroy cancerous cells.
CANCER- TREATMENT

Usually, when cancer has metastasized, prognosis (the
likelihood of survival) is poor.
CANCER PREVENTION



The best way to prevent cancer is to avoid things that can
cause cancer (carcinogens)
Ultraviolet radiation in sunlight can damage genes that
control the cell cycle (skin cancer)
Chemicals in cigarette smoke also affect how cell growth
and division is regulated.
CANCER PREVENTION


Large amounts of alcohol consumption have been linked
to liver cancers
Teenage exposure cell phones has been linked to brain
cancer (NOT A JOKE)
CANCER PREVENTION

Teenage exposure cell phones has been linked to brain
cancer (NOT A JOKE)
Ch 10 SEC 1 HW
1. As a cell gets larger, it needs more nutrients.
Nutrients enter a cell through the cell membrane.
However, as a cell gets larger, it
becomes more difficult for enough nutrients
to enter the cell. If a cell gets too large,
nutrients cannot enter quickly enough for
the cell to survive.
2. from left to right: chromatin; nucleosomes;
DNA (top); histones (bottom)
3. DNA is replicated, and chromosomes begin
to condense.
Ch 10 SEC 2 HW
1. The cell grows and produces new
organelles.
2. mitosis and cytokinesis
3. Spindles connect the centromeres of sister
chromatids to opposite sides of the cell during
metaphase. During anaphase, the spindles
shorten, separating the sister chromatids.
4. top row: Anaphase
second row: Prophase
third row: Telophase
bottom row: Metaphase
Ch 10 SEC 2 HW
5. In animal cells, protein fibers pull the cell
membrane together and cause it to pinch
off, forming two new cells. In plant cells, a
cell plate made of cell wall material forms
in the center of the cell, then slowly grows
outward until it splits the cell in two.
Ch 10 SEC 3 HW
1. Cancer occurs when a cell divides uncontrollably.
This generally occurs because the
cell stops responding to signals that regulate
its movement through the cell cycle.
2. within the cell, nearby cells, or the
environment
3. At the G1 checkpoint, the cell checks that
its environment is favorable for replication
and makes sure that it is healthy. At the G2
checkpoint, the cell checks that its DNA has
been copied correctly and that it is large
enough to divide. At the metaphase checkpoint,
the cell checks that genetic material
has been correctly distributed between the
daughter cells.
Ch 10 SEC 3 HW
4. They tell the cell whether or not to move on
to the next phase in the cell cycle.
5. Benign tumors generally do not spread
to other parts of the body, and most can
be removed by surgery. Malignant tumors
invade nearby healthy tissue and can break
off and travel to other parts of the body.
Malignant tumors are generally harder to
treat than benign tumors.
6. Possible answers: cigarette smoke, benzene,
ultraviolet rays
MITOSIS MOVIE
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