1. The document discusses the cell cycle, cancer, and mutations. It describes the different phases of the cell cycle including interphase and mitosis. 2. It notes that mutations most commonly occur during the S phase of interphase when DNA is being replicated. Cancer occurs when cells lose control mechanisms and divide uncontrollably due to genetic mutations. 3. Mutations can be point mutations like substitutions, or larger chromosomal mutations involving deletions, duplications, inversions or translocations of DNA. These genetic changes can cause cancer when they affect genes regulating cell growth and division.

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The Cell Cycle, Cancer, and
Mutations

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In Unit 6, you discovered that, in mitosis, you have a number
of phases in the division process in which identical daughter
cells are made. Those stages are:
4 Stages: “PMAT”
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Quick Review!

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Phases of the Cell Cycle
• The Cell Cycle, which includes cellular division, also involves the
processes occurring during interphase. A cell is actually in
interphase most of the time! Look at the image below:
• Interphase
– G1 - primary growth
– S - DNA replicated
– G2 - secondary growth
• M – mitosis (PMAT)
• C - cytokinesis

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Interphase
• G1 - Cells undergo majority of growth
• S – The genome (DNA) is replicated
(Synthesized) in this phase along with other small
organelles needed for mitosis later.
NOTE: The S Phase is where most mutations can occur as
DNA is being replicated. Nucleic Acid mismatches can occur at
this time.
• G2 - Assembles sub-cellular machinery such as the
spindles to prepare for Mitosis.

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G2 of Interphase
• A nuclear envelope bounds
the nucleus.
• The nucleus contains one or
more nucleoli (singular,
nucleolus).
• Two centrosomes have
formed by replication of a
single centrosome.
• In animal cells, each
centrosome features two
centrioles.
• Chromosomes, duplicated
during S phase, cannot be
seen individually because
they have not yet condensed.
G2 OF INTERPHASE
Centrosomes
(with centriole pairs) Chromatin
(duplicated)
Nucleolus Nuclear
envelope
Plasma
membrane

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Checks and Balances
• As mentioned in the Amoeba Sister’s Video, cells
have checks and balances that are constantly
accessing their health. Special proteins called
cyclins monitor the cell’s health.
• Cells determined unhealthy self-destruct in what is
called “apoptosis”. In fact, our cells die quite often
for many reasons. Cancer cells however, have lost
this ability.

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Pause, Think, and Share
• What phase is a cell in the
longest period of time?
Interphase
• Replication occurs during
what period of interphase?
S-Phase
• Mutations of a base would
most likely occur during which
phase?
S-Phase Interphase

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• For many cells, the G1 checkpoint seems to
be the most important
• If a cell receives a go-ahead signal at the G1
checkpoint, it will usually complete the S, G2,
and M phases and divide
• If the cell does not receive the go-ahead
signal, it will exit the cycle, switching into a
non-dividing state called the G0 phase
Checks and Balances (cont..)

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• Most cells in your body can detect when they are
overcrowding and signals are produced to stop
dividing.
• Your cells also know to only grow in certain areas
and on particular substrates.
• Cancer cells ignore these signals.
Checks and Balances (cont..)

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Cancer
• Cancer is a disease of uncontrolled cell division. It starts with
a single cell that loses its control mechanisms due to a genetic
mutation. That cell starts dividing without limit, and can
potentially kill the host.
• Normal cells are controlled by several factors. They stay in
the G1 stage of the cell cycle until they are given a specific
signal to enter the S phase, in which the DNA replicates and
the cell prepares for division. Cancer cells enter the S phase
without waiting for a signal.
• Another control: Normal cells are mortal. This means that
they can divide about 50 times or so and then they lose the
ability to divide and eventually die. This “clock” gets re-set
during the formation of the gametes. Cancer cells escape this
process of mortality: they are immortal and can divide
endlessly.

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• Cancer cells that are not eliminated by the immune system
form tumors, masses of abnormal cells within otherwise
normal tissue
• If abnormal cells remain only at the original site, the lump
is called a benign tumor
• Malignant tumors invade surrounding tissues and can
metastasize, exporting cancer cells to other parts of the
body, where they may form additional tumors

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• Recent advances in understanding the
cell cycle and cell cycle signaling have
led to advances in cancer treatment.
• Cancer.org features a number of
treatments that are currently available
to treat a wide variety of cancers:
• http://www.cancer.org/treatment/treatm
entsandsideeffects/treatmenttypes/

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All cancer is genetic, in that it is
triggered by altered genes. Genes
that control the orderly replication of
cells become damaged, allowing
the cells to reproduce without
restraint.
Cancer usually arises in a single cell.
The cell's progress from normal to
malignant to metastatic appears to
follow a series of distinct steps,
each controlled by a different gene
or set of genes.
Many Mutations Can Lead to Cancer

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Even though all cancer is genetic,
just a small portion—perhaps
5–10% —is inherited.
Most cancers come from random
mutations that develop in body
cells during one's lifetime—
either as a mistake when cells
are going through cell division
or in response to injuries from
environmental agents such as
radiation or chemicals.

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Pause, Think, and Share
• Normal cells have checks and
balances that regulate
cell________
Growth
• Most cancers are caused by
genetic_________.
Mutations
• Most cells live only a short
while, but cancer cells are
virtually _________.
Immortal

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Mutations
Mutations are a kind of genetic change.

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As was mentioned before, cancer, is caused by a number of
mutations. These mutations can effect a number of genes.
These almost always include:
• Mutations in genes that are involved in mitosis
• Genes that regulate apoptosis
• Genes that regulate growth and aging
• Genes that stimulate new blood vessel growth
• And genes that keep cells in particular areas
• Let’s look a few ways that mutations can happen.

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A Few types of Mutations

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Kinds of Mutations
Gene Mutations
* Gene mutations involving a change in one
or a few nucleotides are known as point
mutations because they occur at a single
point in the DNA sequence.
Point mutations include substitutions,
insertions, and deletions.

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Kinds of Mutations
Substitutions usually
affect no more than a
single amino acid.
Only one amino acid
will not be produced.
The remaining
sequence is fine.
Hopefully, the protein
created still works. 

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Kinds of Mutations
The effects of insertions or deletions are
more dramatic.
The addition or deletion of a nucleotide causes a shift
in the grouping of codons (groups of 3 nucleotides).
Changes like these are called frameshift mutations.
Not good! The entire reading frame has shifted!

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Kinds of Mutations
Chromosomal Mutations
* Chromosomal mutations
involve changes in the number
or structure of chromosomes.
* Chromosomal mutations
include deletions, duplications,
inversions, and translocations.
Extra Chromosome - Down Syndrome (Trisomy 21)

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Kinds of Mutations
Deletions involve the loss of all or part of a
chromosome.

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Copyright Pearson Prentice Hall
Kinds of Mutations
Duplications produce extra copies of
parts of a chromosome.

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Copyright Pearson Prentice Hall
Kinds of Mutations
Inversions reverse the direction of parts of
chromosomes.

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Copyright Pearson Prentice Hall
Kinds of Mutations
Translocations occurs when part of one
chromosome breaks off and attaches to another.

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Copyright Pearson Prentice Hall
Significance of Mutations
Significance of Mutations
Many mutations have little or no effect on
gene expression.
Some mutations are the cause of genetic
disorders.
Polyploidy is the condition in which an
organism has extra sets of
chromosomes.

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Pause, Think, and Share
• Mutations are a kind of genetic
________.
change
• Insertions and deletions of
nucleotides can cause _______
mutations.
Frameshift
• Replacing a single nucleotide is
called a ________ mutation.
Point