The Cell Cycle and Cell Death

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The Cell Cycle The Cell Cycle and Cell Deathand Cell Death

SNC2DSNC2D

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Cell Cell ReproductionReproductionMitosis in Mitosis in

animal animal cells looks cells looks very like very like mitosis in mitosis in plant cells:plant cells:

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InterphaseInterphase

The cell prepares for cell division by The cell prepares for cell division by growing (producing new proteins and growing (producing new proteins and organelles) and by synthesizing copies organelles) and by synthesizing copies of its DNA (the chromatin).of its DNA (the chromatin).

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ProphaseProphase

During the first phase of mitosis, the During the first phase of mitosis, the chromatin condenses into chromatin condenses into chromosomes and the nuclear chromosomes and the nuclear structure disintegrates. A structure disintegrates. A framework called the mitotic spindle framework called the mitotic spindle forms.forms.

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MetaphaseMetaphase

Next the chromosomes line up in the Next the chromosomes line up in the middle of the cell.middle of the cell.

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MetaphaseMetaphase

Next the chromosomes line up in the Next the chromosomes line up in the middle of the cell.middle of the cell.

In an animal cell, at the end of the In an animal cell, at the end of the spindle fibres at the poles are the spindle fibres at the poles are the centrioles.centrioles.

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AnaphaseAnaphase

The chromosomes separate and are The chromosomes separate and are pulled to opposite ends of the cell.pulled to opposite ends of the cell.

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Telophase and Telophase and CytokinesisCytokinesis

In the last stage of mitosis, the cell In the last stage of mitosis, the cell divides the cytoplasm into two divides the cytoplasm into two portions. The final separation of the portions. The final separation of the cytoplasm into two distinct cells is cytoplasm into two distinct cells is called cytokinesis.called cytokinesis.

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Rate of MitosisRate of Mitosis

Different parts of an organism Different parts of an organism experience different rates of mitosis experience different rates of mitosis (e.g. an onion root tip is where (e.g. an onion root tip is where growth occurs and therefore the growth occurs and therefore the cells divide frequently, every 12 – 36 cells divide frequently, every 12 – 36 hours).hours).

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Rate of MitosisRate of Mitosis

In humans, skin cells (that brush off) In humans, skin cells (that brush off) or intestinal cells (that are broken or intestinal cells (that are broken down by the digestive process) have down by the digestive process) have high rates of mitosis, whereas red high rates of mitosis, whereas red blood cells may last for months.blood cells may last for months.

human skin cells

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ApoptosisApoptosis

The regulated death of a cell that is no The regulated death of a cell that is no longer useful (e.g. white blood cells longer useful (e.g. white blood cells post-infection) or has lost its ability post-infection) or has lost its ability to function efficiently is called to function efficiently is called apoptosisapoptosis..

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ApoptosisApoptosis

The regulated death of a cell that is no The regulated death of a cell that is no longer useful (e.g. white blood cells longer useful (e.g. white blood cells post-infection) or has lost its ability post-infection) or has lost its ability to function efficiently is called to function efficiently is called apoptosisapoptosis..

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ApoptosisApoptosis

The material of the cell is recycled by The material of the cell is recycled by the body.the body.

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CancerCancer

What happens when What happens when damage to a cell damage to a cell impairs its ability to impairs its ability to commit apoptosis commit apoptosis and it divides and and it divides and divides and divides?divides and divides?

cancercancer

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Exponential GrowthExponential Growth

Consider what happens if 1 cell out of Consider what happens if 1 cell out of 1 000 starts dividing uncontrollably.1 000 starts dividing uncontrollably.

The remaining 999 will die as often as The remaining 999 will die as often as they are replaced.they are replaced.

That 1 cell . . . That 1 cell . . .

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Exponential GrowthExponential Growth

# of divisions# of divisions normal cells normal cells cancer cells cancer cells 00 999999 11 11 22 33 44 55 66 77 88 99 1010

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Exponential GrowthExponential Growth

# of divisions# of divisions normal cells normal cells cancer cells cancer cells 00 999999 11 11 999999 22 22 33 44 55 66 77 88 99 1010

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Exponential GrowthExponential Growth

# of divisions# of divisions normal cells normal cells cancer cells cancer cells 00 999999 11 11 999999 22 22 999999 44 33 Keep going. . . . Keep going. . . . 44 55 66 77 88 99 1010

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Exponential GrowthExponential Growth

# of divisions# of divisions normal cells normal cells cancer cells cancer cells 00 999999 11 11 999999 22 22 999999 44 33 999999 88 44 999999 1616 55 999999 3232 66 999999 6464 77 999999 128128 88 999999 256256 99 999999 512512 1010 999999 10241024

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The Beginning of Cancerous Growth

Underlying tissue

Cancers grow more quicklywhere cells divide frequently.

Cancerous growths are called tumours.

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Invasion and Metastasis

Cancer cells can invade surrounding tissues and blood vessels.

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Invasion and Metastasis

Cancer cells then grow at the new locations.

Cancer cells can invade surrounding tissues and blood vessels.

They can also be transported by the circulatory system to other parts of the body (metastasis).

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Malignant versus Benign Tumors

Malignant cells invade neighboring tissues, enter blood vessels, and metastasize to different sites.

Time

Benign tumor cells grow only locally and cannot spread by invasion or metastasis.

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Why Cancer Is Dangerous

Melanoma (skin cancer) cells can travel through the circulatory system.

The cancer that spreads to the liver would be called metastatic melanoma, not liver cancer.Melanoma

(initial tumor)

Liver

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Cancer Detection and Diagnosis

Cancerous Cancerous tumours can tumours can be detected by be detected by medical medical imaging imaging

(x-ray, (x-ray, ultrasound, ultrasound, and MRI and MRI scans).scans).

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Cervical Cancer Screening

Abnormal Pap smear

Normal Pap smear

But even earlier But even earlier stages of stages of cancer can be cancer can be detected by detected by screening screening cells.cells.

AbnormalPap smear

NormalPap smear

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Cervical Cancer Screening

Abnormal Pap smear

Normal Pap smear

But even earlier But even earlier stages of cancer stages of cancer can be detected can be detected by screening by screening cells.cells.

Biopsies similarly Biopsies similarly look at cells look at cells inside suspected inside suspected tumours.tumours.

AbnormalPap smear

NormalPap smear

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Cancer Cells Look Different

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Hyperplasia

HyperplasiaNormal

Sometimes screening detects an excessive rate of cell division called hyperplasia – the cells are still normal and the process is reversible.

An example of hyperplasia would be a callus on your hand.

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Dysplasia

Hyperplasia Mild dysplasiaNormal

Also detectable is dysplasia: excessive growth and abnormal tissue arrangement.

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Milddysplasia

Carcinoma in situ (severe dysplasia) Cancer

(invasive)

Normal Hyperplasia

Dysplasia is often monitored to make sure it doesn’t develop into a metastatic cancer.

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What Causes the

Cell Damage

that Leads to Cancer?

Some viruses or bacteria

HeredityDiet

Hormones

RadiationSome chemicals

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Population-Based Population-Based StudiesStudies

We can determine possible causes of We can determine possible causes of cancer by looking at the incidence in cancer by looking at the incidence in different populations: different populations:

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Incidence in PopulationsIncidence in Populations

The higher incidence The higher incidence of colon cancer in of colon cancer in Japanese families Japanese families that have moved to that have moved to the U.S. suggests the U.S. suggests that it’s behavioural that it’s behavioural and/or and/or environmental environmental factors are what is factors are what is changing the risk.changing the risk.

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0

Number of Cases (per 100,000

people)

Grams (per person per day)

Correlation Between Meat Consumption and Colon Cancer Rates in Different Countries40

30

20

10

30020010080

Look For CorrelationsLook For Correlations

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Some Cancer-Causing Chemicals in Tobacco Smoke

Some Some chemicals chemicals

can damage can damage cellscells

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How Can We Show the How Can We Show the Risk?Risk?

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And Skin Cancer is And Skin Cancer is Correlated with UV Correlated with UV

ExposureExposure

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VirusesViruses

Some viruses are also linked to certain Some viruses are also linked to certain cancers cancers

(e.g. human papillomavirus to cervical (e.g. human papillomavirus to cervical cancer).cancer).

Virus inserts and changes genes forcell growth

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Textbook QuestionsTextbook Questions

p. 36 #1 – 5p. 36 #1 – 5

p. 37 #1 – 5, 7, 8, 10p. 37 #1 – 5, 7, 8, 10