Download Chapter 5 Cancer: DNA Synthesis, Mitosis, and Meiosis

Chapter 5
Cancer:
DNA Synthesis, Mitosis, and Meiosis
Copyright
2007
Pearson Prentice Hall, Inc.
1
Copyright © 2007 Pearson
Prentice©
Hall,
Inc.
Why do we care about DNA structure?
• Because the structure of DNA allows life as we know it to exist
• Because complementary base pairing allows
– new cells to be made with exactly the same DNA as the original cell
• If you can’t do this, you will die!
• A brain cell makes another brain cell, not a liver cell in your head
• Because complementary base pairing allows
– DNA to make an exactly correct RNA
– that then can make an exactly correct protein
• People need to make insulin, stomach digestive enzymes, etc
• If you can’t do this, you will die!
• Because it is Nerdy fun…
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DNA Replication
• The double stranded DNA molecule separates
– at hydrogen bonds that hold the complementary bases together
• Now we have 2 single strands of DNA that are
complementary to each other.
– If there is an A on one strand there is a T on the other strand
• The enzyme DNA polymerase adds the correct base to the
now single strands of DNA
– By complementary base pairing
•
•
•
•
If there is a G, DNA polymerase will add a C
If there is a T, DNA polymerase will add an A
If there is a C, DNA polymerase will add a G
If there is an A, DNA polymerase will add a T
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DNA Replication
• double stranded DNA before replication
• double stranded DNA molecule separates
• Now we have 2 single strands of DNA
that are complementary to each other.
•
• The enzyme DNA polymerase added the
correct base to the two single strands of
DNA to create
– 2 new double stranded DNA molecules
– that are identical to the original double
stranded DNA before replication
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DNA Replication
• Results in two identical DNA molecules
• Each new DNA molecule is half new and half from
the old molecule
• When an entire chromosome is copied, the two
sister chromatids are connected at the centromere
• Now the cell is ready to divide
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DNA Replication
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5.3 The Cell Cycle and Mitosis
• Mitosis is an asexual division
• Is part of the cell cycle
– the life cycle of the cell
• Makes new cells that are exactly the same as the
original cells
– Liver cells make more Liver cells
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The Cell Cycle and Mitosis
For cells that divide by mitosis, there are 3 steps in the
cell cycle:
1. Interphase =
•
DNA replication
2. Mitosis =
•
Replicated DNA/chromosomes divide in half
3. Cytokinesis =
•
cell divides in half
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The Cell Cycle and Mitosis
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Interphase
• Most of a cell’s life is spent in interphase
• Normal functions are carried out
– Nerve cells release neurotransmitters
– Pancreatic cells make and release insulin
• Three stages of interphase:
– G1
• Cell growth
–S
• DNA replication
– G2
• Cell growth and prep for division
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Cell Cycle
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Mitosis
• The purpose of mitosis is to
– separate the sister chromatids
– each new cell has a complete set of chromosomes
Cytokinesis
• The cell itself divides in half creating
– two identical daughter cells
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Cell Cycle
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Cytokinesis
• Animal cells produce a
band of filaments that
divide the cell in half
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Cell Cycle Control and Mutation
• Cells can commit suicide if problems or mutations
occur during the cell cycle
– Cell suicide is called Apoptosis
• Each stage in the cell cycle is an opportunity for
cells to check for mutations or problems
– These are called cell cycle Checkpoints
• At the checkpoints, Cells determine if they are ready
to enter next part of cell cycle
– Only proceed if no mutations are detected
– If they detect mutations, apoptosis occurs
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Cell Cycle Control and Mutation
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Cell Cycle Control and Mutation
• If checkpoints exist and cells apoptose when mutated, how
can a cancerous cell exist?
• If mutations occur in proteins that do the “checking or
detecting” of mutations
– then mutations can slip through the checkpoints undetected
• When the proteins that make the the cell cycle go and stop
are mutated and do not work
– the cell divides uncontrollably
– This results in a tumor
– More and more mutations in this uncontrolled dividing tumor cell
results in a malignant cell = cancer
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Cell Cycle Control and Mutation
• Mutations in the DNA can produce
–
–
–
–
nonfunctioning proteins
Proteins that do something they normally do not
Proteins that do their normal function too much or too fast
Uneffected proteins
• Mutations can be inherited
– Born with the mutations
• Mutations can be induced by exposure to carcinogens that
damage DNA and chromosomes
– Cigarette smoke
– Acetone in nail polish remover
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Cell Cycle Control and Mutation
• Cell cycle control genes are called proto-oncogenes
proto-: before
-onco: cancer
• Proto-oncogenes:
– Normal genes on many different chromosomes
– Regulate cell cycle and cell division
• When mutated, they become oncogenes
• Oncogenes cause
–
–
–
–
–
the cell cycle to bypass or ignore checkpoints
Keep dividing regardless of mutations and problems
More and more mutations occur
More and more cell divisions occur
Bigger and nastier tumors occur
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Cell Cycle Control and Mutation
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Cell Cycle Control and Mutation
• Tumor suppressor genes
– stop cell division when necessary
• Normal cell that does not need to divide
• Mutated cell that needs to apoptose
• Tumor suppressor gene mutations cause
– the cell cycle to go because there is nothing to stop it
– Cells will override the checkpoints
– Cells will divide out of control
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What Is Cancer?
• Benign tumors do not invade surrounding tissue
• Malignant tumors invade surrounding structures:
– are cancer
• Cells from Malignant tumors can break away and
start new cancers elsewhere
– through the process of metastasis
– Benign tumors cannot metastasize
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