10.3
Regulation of Cell Growth

@The controls on cell growth and division can be
turned on and off by contact.@

For example, when an injury such as a broken bone
occurs, cells are stimulated to divide rapidly and start
the healing process. The rate of cell division slows
when the healing process nears completion.
THE DISCOVERY OF CYCLINS

@Cyclins are a family of proteins that regulate the
timing of the cell cycle in eukaryotic cells.@

This graph shows how cyclin levels change
throughout the cell cycle in fertilized clam eggs.
• Apoptosis is programmed cell death.
 a normal feature of healthy organisms
 caused by a cell’s production of self-destructive
enzymes
 occurs in
webbed fingers
development
of infants

Cancer is a disorder in which body cells lose the
ability to control cell growth.

Cancer cells divide uncontrollably to form a mass of
cells called a tumor.
WHAT CAUSES CANCER?

Cancers are caused by defects in genes that regulate
cell growth and division.

Some sources of gene defects are smoking tobacco,
radiation exposure, defective genes, and viral infection.
@A damaged or defective p53 gene is common in
cancer cells. @
 It causes cells to lose the information needed to
respond to growth signals.

A benign tumor is noncancerous.
It does not spread to surrounding
healthy tissue.
A malignant tumor is cancerous.
It invades and destroys
surrounding healthy tissue and
can spread to other parts of the
body.
The spread of cancer cells is called
metastasis. Cancer cells absorb
nutrients needed by other cells,
block nerve connections, and
prevent organs from functioning.
TREATMENTS FOR CANCER

Some localized tumors can be removed by surgery.

Many tumors can be treated with targeted radiation.

Chemotherapy is the use of compounds that kill or
slow the growth of cancer cells.
10.4 CELL DIFFERENTIATION


All organisms start life as just one cell.
Most multicellular organisms pass through an early
stage of development called an embryo, which gradually
develops into an adult organism.
DEFINING DIFFERENTIATION

The process by which cells become
specialized is known as
differentiation.

During development, cells
differentiate into many different types
and become specialized to perform
certain tasks.

Differentiated cells carry out the
jobs that multicellular organisms need
to stay alive.
STEM CELLS

Stem cells are unspecialized cells from which
differentiated cells develop.

There are two types of stem cells: embryonic and
adult stem cells.
EMBRYONIC STEM CELLS



Embryonic stem cells are found in the inner cells
mass of the early embryo.
Embryonic stem cells are pluripotent.
Researchers have grown stem cells isolated from
human embryos in culture. Their experiments confirmed
that embryonic stem cells have the capacity to produce
most cell types in the human body.
ADULT STEM CELLS

Adult organisms contain some types of stem cells.

Adult stem cells are multipotent. They can produce
many types of differentiated cells.

Adult stem cells of a given organ or tissue typically
produce only the types of cells that are unique to that
tissue.
POTENTIAL BENEFITS

Stem cell research may lead to new ways to repair
the cellular damage that results from heart attack,
stroke, and spinal cord injuries.

@One example is the approach to reversing heart
attack damage illustrated below.@