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Lesson Overview
Regulating the Cell Cycle
Lesson Overview
10.3
Regulating the Cell Cycle
10.4
Cell Differentiation
Lesson Overview
Regulating the Cell Cycle
Guiding Questions:
How is the cell cycle regulated?
How do cancer cells differ from other cells?
What causes cancer & how can it be controlled?
How do cells become specialized for different functions?
What are stem cells?
Lesson Overview
Regulating the Cell Cycle
But first….let’s review the basics of
the cell cycle:
Genetic information in the form of DNA
Cell cycle= process of cell division
 The cell grows;
 DNA is copied;
 The contents of the nucleus are
divided;
 Cytoplasm is divided;
 Two new cells exactly like the
original cell!
Lesson Overview
Regulating the Cell Cycle
Controls on Cell Division
How is the cell cycle regulated?
The cell cycle is controlled by regulatory proteins both inside and outside
the cell.
Lesson Overview
Regulating the Cell Cycle
The controls on cell growth and division can be turned on and off.
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.
Lesson Overview
Regulating the Cell Cycle
Also, recall…
one of the major characteristics of living things is the ability to GROW
an adult doesn't have bigger cells, they have more cells
You can grow too many cells!!!
Lesson Overview
Regulating the Cell Cycle
An Interesting Fact About Cell Division:
Not all cells move through the cell
cycle at the same rate
Ex: most muscle cells & nerve cells do not divide
at all once they have developed
Ex: skin cells and cells lining our intestines
complete the cell cycle every 24-28 hours
Ex: frog embryo cells take less than one hour!
Lesson Overview
Regulating the Cell Cycle
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.
Lesson Overview
Regulating the Cell Cycle
Regulatory Proteins
Internal regulators are proteins that respond to events inside a cell. They
allow the cell cycle to proceed only once certain processes have
happened inside the cell.
External regulators are proteins that respond to events outside the cell.
They direct cells to speed up or slow down the cell cycle.
Growth factors are external regulators that stimulate the growth and
division of cells. They are important during embryonic development and
wound healing.
Lesson Overview
Regulating the Cell Cycle
Apoptosis
Apoptosis is a process of programmed cell death.
Apoptosis plays a role in development by shaping the structure of
tissues and organs in plants and animals. For example, the foot of a
mouse is shaped the way it is partly because the toes undergo
apoptosis during tissue development.
Lesson Overview
Regulating the Cell Cycle
A mistake (MUTATION) in the DNA (GENES) that codes for one or more of
these control factors/enzymes could lead to a LOSS OF CONTROL OF
THE CELL CYCLE.
Lesson Overview
Regulating the Cell Cycle
Cancer: Uncontrolled Cell Growth
How do cancer cells differ from other
cells?
Cancer cells do not respond to the
signals that regulate the growth of most
cells. As a result, the cells divide
uncontrollably.
Lesson Overview
Regulating the Cell Cycle
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.
Lesson Overview
Regulating the Cell Cycle
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.
Lesson Overview
Regulating the Cell Cycle
Lesson Overview
Regulating the Cell Cycle
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.
Lesson Overview
Regulating the Cell Cycle
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.
Old Mastectomy
Vs.
New Mastectomy
Lesson Overview
Regulating the Cell Cycle
From One Cell to Many
How do cells become specialized for different functions?
During the development of an organism, cells differentiate into many types
of cells.
Lesson Overview
Regulating the Cell Cycle
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.
Lesson Overview
Regulating the Cell Cycle
During development, an organism’s cells become more differentiated and
specialized for particular functions.
For example, a plant has specialized cells in its roots, stems, and leaves.
Lesson Overview
Regulating the Cell Cycle
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.
Lesson Overview
Regulating the Cell Cycle
Mapping Differentiation
In some organisms, a cell’s role is determined at a specific point in
development.
In the worm C. elegans, daughter cells from each cell division follow a
specific path toward a role as a particular kind of cell.
Lesson Overview
Regulating the Cell Cycle
Differentiation in Mammals
Cell differentiation in mammals is controlled by a number of interacting
factors in the embryo.
Adult cells generally reach a point at which their differentiation is
complete and they can no longer become other types of cells.
Lesson Overview
Regulating the Cell Cycle
Stem Cells and Development
What are stem cells?
The unspecialized cells from which differentiated cells develop are known
as stem cells.
Lesson Overview
Regulating the Cell Cycle
One of the most important questions in biology is how all of the specialized,
differentiated cell types in the body are formed from just a single cell.
Biologists say that such a cell is totipotent, literally able to do everything,
to form all the tissues of the body.
Only the fertilized egg and the cells produced by the first few cell divisions
of embryonic development are truly totipotent.
Lesson Overview
Regulating the Cell Cycle
Human Development
After about four days of development, a human
embryo forms into a blastocyst, a hollow ball
of cells with a cluster of cells inside known as
the inner cell mass.
The cells of the inner cell mass are said to be
pluripotent, which means that they are
capable of developing into many, but not all, of
the body's cell types.
Lesson Overview
Regulating the Cell Cycle
Stem Cells
Stem cells are unspecialized cells from which differentiated cells
develop.
There are two types of stem cells: embryonic and adult stem cells.
Lesson Overview
Regulating the Cell Cycle
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.
Lesson Overview
Regulating the Cell Cycle
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.