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Chapter 5

Cancer:

DNA Synthesis, Mitosis, and Meiosis

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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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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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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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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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• 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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Cell Cycle Control and Mutation

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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