chapter 5 cancer: dna synthesis, mitosis, and meiosiscmalone/pdf100/ch05-2cancer.pdf · chapter 5...
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1Copyright © 2007 Pearson Prentice Hall, Inc.
Chapter 5
Cancer:
DNA Synthesis, Mitosis, and Meiosis
Copyright © 2007 Pearson Prentice Hall, Inc.
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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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3Copyright © 2007 Pearson Prentice Hall, Inc.
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 arecomplementary 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 thenow 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 DNAthat are complementary to each other.
•
• The enzyme DNA polymerase added thecorrect base to the two single strands ofDNA to create– 2 new double stranded DNA molecules
– that are identical to the original doublestranded DNA before replication
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5Copyright © 2007 Pearson Prentice Hall, Inc.
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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 thecell cycle:
1. Interphase =• DNA replication
2. Mitosis =• Replicated DNA/chromosomes divide in half
3. Cytokinesis =• cell divides in half
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10Copyright © 2007 Pearson Prentice Hall, Inc.
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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14Copyright © 2007 Pearson Prentice Hall, Inc.
Cell Cycle
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15Copyright © 2007 Pearson Prentice Hall, Inc.
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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• 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
Cell Cycle Control and Mutation
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• 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 thatdamage DNA and chromosomes– Cigarette smoke
– Acetone in nail polish remover
Cell Cycle Control and Mutation
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• 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
Cell Cycle Control and Mutation
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21Copyright © 2007 Pearson Prentice Hall, Inc.
Cell Cycle Control and Mutation
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22Copyright © 2007 Pearson Prentice Hall, Inc.
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• 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
Cell Cycle Control and Mutation
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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