The Cell Cycle, Mitosis, and Cancer

Why can’t we be one big cell?

• There are limits to cell growth:

• DNA “overload” – DNA is the blueprint for proteins

– Big cells lead to “information overload”• Cell/DNA cannot make all of the proteins

that it needs

Example—if we only had one copy of the biology book for the whole school

Why can’t we be one big cell?

• Exchange of materials– Diffusion is only fast/efficient over short

distances

– Getting enough nutrients, waste, etc. in/out becomes too difficult in a big cell

Why can’t we be one big cell?

• Surface area to volume ratio– Volume increases much faster than

surface area

– Cell membrane does not have enough area to allow all nutrients and waste to diffuse in and out efficiently

                                                    

  

ParametersCase I

Case II

Case III

Case IV

Length (L) 1 2 3 4

Face Area (L2) 1 4 9 16

Volume (L3) 1 8 27 64

Surface Area(L2 x 6 faces) 6 24 54 96

Area/Volume ratio 6 3 2 1.5

How do we grow and get bigger if cells can

only be so big?

CELL DIVISION

Cell Division and the Cell Cycle

• Cell cycle: the ‘life cycle’ of a cell–A “parent” cell grows, prepares,

and then divides to form two identical “daughter” cells.

–Includes interphase and mitosis

1 parent cellCell grows,

DNA duplicates, Cell pulls apart 2 identical

daughter cells

Cell Division

• Mitosis is asexual reproduction. Each cell receives its own set of DNA, but there is NO GENETIC DIFFERENCE between the parent and daughter cells.

Where Does Mitosis Occur?

Nails

Skin

Hair

Intestines

Bones

Muscles

In other words…Mitosis occurs here,

there, and everywhere (almost!)

—Old McDonald

Cells that DO NOT Undergo Mitosis

Cell Division

• Mitosis occurs only in somatic (body) cells– Gametes (sex) cells undergo

another process, called meiosis.

– (We’ll talk about that later.)

Cell Division

• Humans have 23 chromosome pairs.

After mitosis, how many TOTAL chromosomes does each cell have?

The cell cycle

INTERPHASE: G1• Cell grows rapidly (G for growth)

- The cell grows, makes proteins, and serves its purpose in the body

Interphase: S• S phase; DNA is copied

- S for “synthesis”

ChromosomesChromosomes

New cells must be exactly like New cells must be exactly like the original - DNA is copied the original - DNA is copied before division can beginbefore division can begin

Genetic information (DNA) is Genetic information (DNA) is found in the nucleusfound in the nucleus

Sister chromatidSister chromatid

centromerecentromere

Interphase: G2• Cell grows more, makes more organelles, and prepares for mitosis (cell division) --- “get ready 2 go”

END OF INTERPHASE

G2 checkpoint helps maintain genetic (DNA) stability by repairing/stopping the replication of damaged cells. ---Important focus in understanding cancer

InterphaseInterphase

MitosisMitosis

The Life of a CellThe Life of a Cell

(M phase)(M phase)

M phase• Cell divides into 2 identical daughter cells

• Daughter cells are identical to each other and to the parent cells

• Mitosis is divided into 4 phases (P, M, A, T)

P = Prophase• Longest phase of mitosis

• DNA (chromatin) coils up and condenses to form visible chromosomes

• Nuclear membrane breaks up

• Spindle fibers form

•Centrioles (animals only) begin to migrate to opposite ends of the cell

M = Metaphase• Chromosomes are

connected to spindle fibers at their centromeres

• Chromosomes line up across the Middle of the cell

Sister chromatidSister chromatid

centromerecentromere

A = Anaphase

• Centromeres split Apart

• Spindle fibers pull chromatids to opposite poles ofthe cell

T = Telophase• Chromosomes

uncoil

• Spindle fibers break down

• Two new nuclei start to form

Cytokinesis

• Occurs after mitosis

• Cytoplasm divides

• Cells pinch apart

Cytokinesis in Plants

• In plants, a cell plate forms to divide the cells and becomes the cell wall

INTERPHASEINTERPHASE

PROPHASEPROPHASE

METAPHASEMETAPHASE

ANAPHASEANAPHASE

TELOPHASE/CYTOKINESISTELOPHASE/CYTOKINESIS

dd

aa

cc

bb ee

D, A, C, B, ED, A, C, B, E

Put the following stages of mitosis (interphase, prophase, metaphase, anaphase,

telophase/cytokinesis in order.

What happens when…

MITOSIS GOES WRONG…?

CAUTION…

• You’re about to learn about one of biggest human killers in all of the world.

• Responsible for 7.6 million deaths…

• …in 2007 alone.

• 7.6 Million is roughly equal to the entire population of North Carolina.

• The deadly killer?

CANCER

Cancer

• Uncontrolled cell division

• May be caused by:– Environmental

factors– Changes in enzyme

production in the cell cycle

Normal Control of the Cell Cycle• Enzymes (cyclins) control the cell cycle

– Series of enzymes monitor the cell’s progress from phase to phase

Controlling Cell DivisionControlling Cell Division

- Cells have internal & external - Cells have internal & external regulators that control cell divisionregulators that control cell division

- Cancer cells do not respond to the - Cancer cells do not respond to the regulators, which leads to uncontrolled cell regulators, which leads to uncontrolled cell growthgrowth

- Cancer cells can form tumors- Cancer cells can form tumors* benign tumors* benign tumors* malignant tumors (metastasize)* malignant tumors (metastasize)

Unregulated Cell Growth

Celebrities with Cancer

• Cancer doesn’t discriminate – anyone is susceptible, and anyone can be diagnosed.

• BUT, why is it that some groups seem to be more prone to cancer than others?

Why do doctors think cancer might be genetic?

• Certain mutations within our cells canbe inherited fromone of our parents

Genetics Involved in Cancer

• Two genes involved in cancer that we will talk about are:– Oncogenes

– Tumor Suppressor Genes

Oncogenes

• Oncogenes code for proteins that initiate/start cell division (they tell the cell “Hey - start dividing!”)

Tumor Suppressor Genes

• Code for proteins that stop the cell from dividing (they tell the cell “Hey – stop dividing!”)

Development of Cancer

• Cancer can develop when: – an oncogene is mutated AND one TS

gene is mutated– OR when both tumor suppressor genes

are mutated

• It’s like treading water – you use both arms to stay above water, but even if you take away one arm you can manage to stay afloat. But, if you take away both arms, you have no arms to tread water with and you sink.

Development of Cancer

• When two of these genes are mutated, cell division is no longer regulated, and the cell divides uncontrollably, forming a mass of cells known as a tumor.

Why are tumors dangerous?

• Tumors can have a dangerous impact when they form around tissues that are sensitive and vital.

• They put pressure on nearby tissues and organs.

THE EFFECTS OF A TUMOR IN OUR BODY

Why are tumors dangerous?

• Cancerous cells can also invade other tissues/organs, damaging or disabling them in the process.

• This makes our tissues and organs more susceptible to infections.

How does cancer spread?

• Cells that form a tumor are called “malignant”

• Tumor cells continue to produce cells via mitosis, and the tumor releases those malignant cells into the blood stream

• In the blood stream, these cells are exposed to the immune system…

How does cancer spread?

• Cells that survive the attacks from our immune system travel through our body, and they can adhere to muscle linings, tissues, or other organs.

• Tumor formation begins in a new location of the body as these malignant cells begin to divide in the new location.

• This process is called metastasis

Metastatic Colon Cancer

Why is Cancer more common in older people?

• With every cell division, the risk of DNA mutation increases

Cells in their body have already been through many divisions and many cycles. Each time a cell divides and copies its DNA, it increases the risk of a genetic mutation

Take a skin cell versus a bone cell. In which would a mutation be more likely to occur?

Cancer Treatments

SurgeryDoctors may choose to physically remove a tumorwith surgery. They may alsoremove some healthy tissueas a preventative measureto make sure that all potentially malignant cellsare removed and that metastasis is not an option.

Cancer Treatments

ChemotherapyChemo is a treatment for cancer that stops a certain process in our body. What would you guess it stops?

*Hint: it usually inhibits the oncogene in our cells

What are some side effects of chemotherapy?

Cancer Treatments

Not only does chemo stop the division of malignant cells in our body, it stops division of ALL the cells in our body. Thinking back to the side effects of chemo, what cells are being affected? Where did division stop?

Closing Question

How does mitosis relate to cancer?