CELL DIVISION PART 2Cell Cycle and Mitosis and Loss of Cell Cycle Control

Targets 7-14

A cell cycle is: the regular sequence of growth and division that cells undergo.

There are three main stages during a cell cycle:Stage 1= Interphase Stage 2= Mitosis (Prophase, Metaphase, Anaphase,

Telophase)Stage 3= Cytokinesis

This figure represents the amount of time that each stage of the cell cycle takes

G1

S

G2

Interphase

Mitosis

Cytokinesis

PM

AT

Stage 1: Interphase (3 parts) During this stage, a cell grows, copies its

chromosomes, and prepares to divide.

1. G1: most of cell’s life is spent here in growth and development.

2. S (synthesis): Chromosomes (in the form of chromatin) are copied in the nucleus = DNA replication, centrioles are also copied.

3. G2: Cell continues to grow, copies cell organelles, prepares to divide.

This part of cell cycle lasts the longest—cell spends the majority of its life here!

Checkpoint Animation

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__control_of_the_cell_cycle.html

There are checkpoints to control the rate that cells go through the cell cycle.

2 of the 3 checkpoints occur during interphase:

G1 checkpoint: most important checkpoint; cells are stopped during G1, and must receive signals in order to continue on to the S phase.

○ If the cell does not receive a go-ahead signal, it will exit the cell cycle and go to G0, a non-dividing state (mature nerve cells and muscle cells typically do this!).

G2 checkpoint: makes sure that DNA has been replicate correctly during the S phase. Passes on to mitosis if DNA replication happens correctly

This figure represents the area of each checkpoint

G1

S

G2

Interphase

Mitosis

Cytokinesis

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G2 Checkpoint

G1 Checkpoint

Stage 2: Mitosis During this stage, a cell’s

nucleus divides into 2 new nuclei (4 phases in mitosis).

Mitosis checkpoint: makes sure a complete set of chromosomes will go into each daughter cell. If all is well-passes on to cytokinesis

This figure represents the area of each checkpoint

G1

S

G2

Interphase

Mitosis

Cytokinesis

PM

AT

M Checkpoint

G2 Checkpoint

G1 Checkpoint

Cells Alive Animation…

http://www.cellsalive.com/cell_cycle.htm

1. Prophase:

a) Chromatin condenses into chromosomes (with sister chromatids attached by centromeres).

b) Nuclear membrane starts to break down.

c) Centrioles begin to separate to opposite ends of the cell and spindle fibers form from the centrioles.

Animal Cells

Plant Cell Prophase

2. Metaphase:

a) Centrioles are at opposite ends of cell.

b) Sister chromatids line up in center of cell and attach to spindle fibers at their kinetochores within the centromeres.

Animal Cells

Plant Cell Metaphase

3. Anaphase:

a) Chromatids are pulled apart at the centromere.

b) Spindle fibers pull chromatids toward opposite ends of cell (to centrioles).

Animal Cells

Plant Cell Anaphase

4. Telophase:a) New nuclear membranes form around

chromosomes at each end of cell.

b) Chromosomes reach opposite ends of the cell

c) The Chromosomes uncoil into chromatin

Animal Cells

Plant Cell Telophase

Early Telophase Late Telophase

Stage 3: Cytokinesis During this stage, the cytoplasm completely divides

to make 2 new identical cells.The cell’s organelles are divided between the 2 new

cells.In animal cells, the cleavage furrow completely pinches

in to make 2 cells.In plant cells, the cell plate becomes the cell wall and

completely separates the 2 cells.At the end of cytokinesis, 2 new identical daughter cells

are formed!

Mitosis animation

This figure represents the amount of time that each stage of the cell cycle takes as well the

various checkpoints.

G1

S

G2

Interphase

Mitosis

Cytokinesis

PM

AT

M Checkpoint

G2 Checkpoint

G1 Checkpoint

Cells Alive Animation

http://www.cellsalive.com/mitosis.htm

WHY/HOW DO WE GET CANCER?

HOW DO WE TREAT IT?Objectives 12-13

Normal Cell Characteristics

1) Density Dependent Inhibition – crowding of cells causes them to STOP dividing

• In the picture, cells will divide until a single layer forms along the bottom

• If you take out some cells, they will divide until the bottom is full again

2) Anchorage Dependence – cells must be attached to something (like the bottom of a container or extracellular fibers)

Cancer Cell Characteristics

1) Lack Density Dependent Inhibition – crowding of cells DOES NOT cause them to STOP dividing• In the picture, cells

will continue to divide, piling on top of each other

2) Do NOT exhibit Anchorage Dependence – cells DO NOT have to be attached to anything

Benign Tumors v. Malignant Tumors

Benign - abnormal cells remain the original site of development (lump) = do NOT cause serious problems and can be removed (usually)

Malignant – abnormal cells have divided often and have spread to surrounding area = CANCERMay have a strange number of chromosomesNo longer function productivelySecrete molecules to tell the blood vessels to grow

to them to “feed” themMetastasis - cells lose attachment to other cells,

travel in the blood stream, and divide uncontrollably in a new location = the cancer has SPREAD

Cancer Treatments Radiation – treats localized cancer with high-

energy wavesDamages cancer DNA more than normal DNA due to

cancer DNA’s inability to fix the errors (normal cells can fix the damage)

Chemotherapy – treats unknown cancer or cancer that has metastasized Damages actively dividing cells (like cancer cells)

○ explains why your hair falls out, why you feel sick and why your immune system is lowered, but you can continue to function

Example : the drug Taxol freezes the spindles and stops cell division during metaphase

Alternative Cancer Treatments

Gene Therapy – insert genetic material (DNA or RNA) into cells to fight or prevent disease

Targeted cancer therapy – drugs that target molecules that are ONLY present on cancer cells to prevent dividing

http://www.cancer.gov/flash/targetedtherapies/breast/main.html#