Chapter 10

Cell Growth and Division

Cell Division

Before a cell becomes too large, it undergoes cell division,

in which the cell divides and becomes 2 “daughter” cells.

Before cell division occurs, the cell replicates all of its DNA.

Each daughter cell then receives its own copy of DNA, or

genetic information.

Each daughter cell has an increased ratio of surface area to

volume which allows for sufficient exchange of materials

with the environment.

Cell Division

In eukaryotes, cell division occurs in 2 main stages:

Mitosis- the first stage

Cytokinesis- the second stage- division of the cytoplasm

Many organisms, particularly unicellular organisms,

reproduce via mitosis and cytokinesis. This is a form of

asexual reproduction, since the cells produced by mitosis are

genetically identical to the parent cell.

Mitosis is also the source of new cells when a multicellular

organism grows and develops.

Chromosomes Chromosomes carry the genetic information of an individual

organism, and are responsible for passing genetic information between generations.

Organisms have a characteristic number of chromosomes Humans have 23 pairs or 46 chromosomes.

Before cell division, chromosomes are replicated and form two identical “sister” chromatids. When the cell divides, the sister chromatids separate from each other. One chromatid goes to each of the two new cells. Each pair of chromatids is attached at the centromere, near the middle of the chromatid.

Centromere

Sister Chromatids

The Cell Cycle

The Cell Cycle- a series of events that cells go through.

During the cell cycle, a cell grows, prepares for division, and

divides to form two daughter cells, each of which begins the

cell cycle again.

Consists of 4 phases

M Phase- includes mitosis and cytokinesis

S Phase- chromosome replication, synthesis of DNA occurs

G1 – cells do most of their growing. In this phase, cells increase in size

and synthesize new proteins and organelles.

G2 – the shortest phase of interphase, organelles and molecules required

for cell division are produced. At the end of this phase, the cell is ready to

enter the M phase and begin cell division.

Inte

rph

ase

The Cell Cycle

M Phase

4 Phases of Mitosis

Prophase- first and longest phase (~50-60%) of mitosis.

Chromosomes become visible. Centrioles separate and move

toward poles.

Centrioles lie within The centrosome and helps

organize the spindle

which works to separate

the chromosomes.

Near the end of prophase,

the nuclear envelope begins

to break down.

Spindle

forming

Centriole

4 Phases of Mitosis

Metaphase- chromosomes line up across the middle of the

cell. Microtubules connect the centromere of each

chromosome to the two poles of the spindle.

Microtubules

connect to

centromere of

chromosome.

4 Phases of Mitosis

Anaphase- the centromeres that join the sister chromatids

split, allowing the sister chromatids to separate and become

individual chromosomes. Anaphase ends when

chromosomes reach opposite poles and stop moving.

New individual

chromosomes-

formed from sister

chromatids

4 Phases of Mitosis

Telophase- final phase of mitosis- nuclear envelope

re-forms, spindle breaks apart, and nucleus becomes visible.

Cytokinesis

Cytokinesis- Cytoplasm divides. Cytokinesis typically

occurs simultaneously with telophase. Each part now

contains its own nucleus, DNA, and cell organelles.

In plants, a cell plate forms between the divided nuclei and

gradually develops into a separating membrane.

Binary Fission

Binary Fission-

cells grow to double

their size and divide

to form two cells.

Occurs in

prokaryotes and

single celled

eukaryotes.

Single celled

eukaryotes must still

go through mitosis

prior to division.

Exit Slip

Name in order the stages of the cell cycle, beginning with the

G1 phase.

Warm Up Exercise

When you came in, you picked up a bag with 7 images from

the cell cycle.

Place the images in order as best you can, then compare with a

partner.

Once you have reached a consensus, write the letters on your

warm up sheet, and label each phase.

Finally, explain what happens during that specific phase of cell

division.

Regulating the Cell Cycle

Different types of cells go through the cell cycle at different

rates.

Experiments show that normal cells will reproduce until they

come into contact with other cells.

When cells come into contact with other cells, they respond by

not growing. This is called contact inhibition.

This demonstrates that controls on cell growth and division can

be turned on and off.

Contact Inhibition

Cell Cycle Regulators

Cells in mitosis are regulated by a series of proteins called

cyclins which increases and decrease during the cell cycle.

Internal Cell Regulation: proteins that respond to events

inside the cell. Allow the cell cycle to proceed only when

certain processes have happened inside the cell.

External Cell Regulation: proteins that respond to events

outside the cell. Direct cells to speed up or slow down the

cell cycle. (ie: growth factors)

Cyclins

A sample of cytoplasm

is removed from a cell

in mitosis.

The sample is injected

into a second cell in

G2 of interphase.

As a result, the second

cell enters mitosis.

Uncontrolled Cell Growth

Cancer- a disorder in which some of the body’s own cells

lose the ability to control cell growth.

Cancer cells do not respond to the signals that regulate the

growth of most cells. As a result, these cells divide

uncontrollably and form masses of cells called tumors that can

damage the surrounding tissues.

Uncontrolled Cell Growth

Benign- cancer cells typically remain clustered together and

are relatively harmless.

Malignant- cancer cells break away and metastasize from

the tumor. These can be carried elsewhere in the body.

Carcinogens- substances known to promote the

development of cancer.

Cancer/Stem Cell Discussion

Reading on pg. 253

BioDetectives video- Skin Cancer: Deadly Cells

Exit Slip

Anticancer drugs prevent microtubules from forming spindle

fibers. Why do you think these drugs might be effective

treatments for cancer?