Transcript Cell Division and Reproduction

Lesson Overview
Cell Growth, Division, and Reproduction
Lesson Overview
10.1 Cell Growth, Division,
and Reproduction
Lesson Overview
Cell Growth, Division, and Reproduction
Limits to Cell Size
What are some of the difficulties a cell faces as it increases in size?
The larger a cell becomes, the more demands the cell places on its DNA.
In addition, a larger cell is less efficient in moving nutrients and waste
materials across its cell membrane.
Lesson Overview
Cell Growth, Division, and Reproduction
Information “Overload”
Compare a cell to a growing
town. The town library has a
limited number of books. As
the town grows, these limited
number of books are in
greater demand, which limits
access.
A growing cell makes greater
demands on its genetic
“library.” If the cell gets too
big, the DNA would not be
able to serve the needs of the
growing cell.
Lesson Overview
Cell Growth, Division, and Reproduction
Exchanging Materials
Food, oxygen, and water enter a cell through the cell membrane. Waste
products leave in the same way.
The rate at which this exchange takes place depends on the surface
area of a cell.
The rate at which food and oxygen are used up and waste products are
produced depends on the cell’s volume.
The ratio of surface area to volume is key to understanding why cells
must divide as they grow.
Lesson Overview
Cell Growth, Division, and Reproduction
Ratio of Surface Area to Volume
Imagine a cell shaped like a cube. As the length of the sides of a cube
increases, its volume increases faster than its surface area, decreasing
the ratio of surface area to volume.
If a cell gets too large, the surface area of the cell is not large enough to
get enough oxygen and nutrients in and waste out.
Lesson Overview
Cell Growth, Division, and Reproduction
Traffic Problems
To use the town analogy again, as
the town grows, more and more
traffic clogs the main street. It
becomes difficult to get
information across town and
goods in and out.
Similarly, a cell that continues to
grow would experience “traffic”
problems. If the cell got too large,
it would be more difficult to get
oxygen and nutrients in and waste
out.
Lesson Overview
Cell Growth, Division, and Reproduction
Division of the Cell
Before a cell grows too large, it divides into two new “daughter” cells in
a process called cell division.
Before cell division, the cell copies all of its DNA.
It then divides into two “daughter” cells. Each daughter cell receives a
complete set of DNA.
Cell division reduces cell volume. It also results in an increased ratio of
surface area to volume, for each daughter cell.
Lesson Overview
Cell Growth, Division, and Reproduction
Cell Division and Reproduction
How do asexual and sexual reproduction compare?
The production of genetically identical offspring from a single parent is
known as asexual reproduction.
Offspring produced by sexual reproduction inherit some of their genetic
information from each parent.
Lesson Overview
Cell Growth, Division, and Reproduction
Sexual Reproduction
In sexual reproduction, offspring are produced by the fusion of two sex
cells – one from each of two parents. These fuse into a single cell
before the offspring can grow.
The offspring produced inherit some genetic information from both
parents.
Most animals and plants, and many single-celled organisms, reproduce
sexually.
Lesson Overview
Cell Growth, Division, and Reproduction
Comparing Sexual and Asexual
Reproduction
Lesson Overview
Cell Growth, Division, and Reproduction
Lesson Overview
10.2 The Process
of Cell Division
Lesson Overview
Cell Growth, Division, and Reproduction
Chromosomes
The genetic information that is passed on from one generation of cells to
the next is carried by chromosomes.
Every cell must copy its genetic information before cell division begins.
Each daughter cell gets its own copy of that genetic information.
Cells of every organism have a specific number of chromosomes.
Lesson Overview
Cell Growth, Division, and Reproduction
Prokaryotic Chromosomes
Prokaryotic cells lack nuclei. Instead, their DNA molecules are found in
the cytoplasm.
Lesson Overview
Cell Growth, Division, and Reproduction
Eukaryotic Chromosomes
In eukaryotic cells, chromosomes are located in the nucleus, and are
made up of chromatin.
Lesson Overview
Cell Growth, Division, and Reproduction
The Cell Cycle
What are the main events of the cell cycle?
During the cell cycle, a cell grows, prepares for division, and divides to
form two daughter cells.
Lesson Overview
Cell Growth, Division, and Reproduction
The Prokaryotic Cell Cycle
Binary fission is a form of asexual
reproduction during which two
genetically identical cells are produced.
For example, bacteria reproduce by
binary fission.
Lesson Overview
Cell Growth, Division, and Reproduction
The Eukaryotic Cell Cycle
The eukaryotic cell cycle consists of
four phases: G1, S, G2, and M.
Lesson Overview
Cell Growth, Division, and Reproduction
G1 Phase: Cell Growth
In the G1 phase, cells increase in
size and synthesize new proteins
and organelles.
Lesson Overview
Cell Growth, Division, and Reproduction
S Phase: DNA Replication
In the S (or synthesis) phase, new
DNA is synthesized when the
chromosomes are replicated.
Lesson Overview
Cell Growth, Division, and Reproduction
G2 Phase: Preparing for Cell Division
In the G2 phase, many of the
organelles and molecules required
for cell division are produced.
Lesson Overview
Cell Growth, Division, and Reproduction
M Phase: Cell Division
In eukaryotes, cell division occurs
in two stages: mitosis and
cytokinesis.
Mitosis is the division of the cell
nucleus.
Cytokinesis is the division of the
cytoplasm.
Lesson Overview
Cell Growth, Division, and Reproduction
Important Cell Structures Involved in
Mitosis
Chromatid – each strand of a duplicated chromosome
Centromere – the area where each pair of chromatids is joined
Centrioles – tiny structures located in the cytoplasm of animal cells that
help organize the spindle
Spindle – a fanlike microtubule structure that helps separate the
chromatids
Lesson Overview
Cell Growth, Division, and Reproduction
Prophase
During prophase, the first
phase of mitosis, the duplicated
chromosome condenses and
becomes visible.
Lesson Overview
Cell Growth, Division, and Reproduction
Prophase
During prophase, the first
phase of mitosis, the duplicated
chromosome condenses and
becomes visible.
The centrioles move to
opposite sides of nucleus and
help organize the spindle.
Lesson Overview
Cell Growth, Division, and Reproduction
Prophase
During prophase, the first
phase of mitosis, the duplicated
chromosome condenses and
becomes visible.
The centrioles move to
opposite sides of nucleus and
help organize the spindle.
The spindle forms and DNA
strands attach at a point called
their centromere.
The nucleolus disappears and
nuclear envelope breaks down.
Lesson Overview
Cell Growth, Division, and Reproduction
Metaphase
During metaphase, the second
phase of mitosis, the centromeres
of the duplicated chromosomes
line up across the center of the
cell.
Lesson Overview
Cell Growth, Division, and Reproduction
Metaphase
During metaphase, the second
phase of mitosis, the centromeres
of the duplicated chromosomes
line up across the center of the
cell.
The spindle fibers connect the
centromere of each chromosome
to the two poles of the spindle.
Lesson Overview
Cell Growth, Division, and Reproduction
Anaphase
During anaphase, the third phase
of mitosis, the centromeres are
pulled apart and the chromatids
separate to become individual
chromosomes.
Lesson Overview
Cell Growth, Division, and Reproduction
Anaphase
During anaphase, the third phase
of mitosis, the centromeres are
pulled apart and the chromatids
separate to become individual
chromosomes.
The chromosomes separate into
two groups near the poles of the
spindle.
Lesson Overview
Cell Growth, Division, and Reproduction
Telophase
During telophase, the fourth and
final phase of mitosis, the
chromosomes spread out into a
tangle of chromatin.
Lesson Overview
Cell Growth, Division, and Reproduction
Telophase
During telophase, the fourth and
final phase of mitosis, the
chromosomes spread out into a
tangle of chromatin.
A nuclear envelope re-forms around
each cluster of chromosomes.
Lesson Overview
Cell Growth, Division, and Reproduction
Telophase
During telophase, the fourth and
final phase of mitosis, the
chromosomes spread out into a
tangle of chromatin.
A nuclear envelope re-forms around
each cluster of chromosomes.
The spindle breaks apart, and a
nucleolus becomes visible in each
daughter nucleus.
Lesson Overview
Cell Growth, Division, and Reproduction
Cytokinesis
How do daughter cells split apart after mitosis?
Cytokinesis completes the process of cell division – it splits one cell into
two.
Lesson Overview
Cell Growth, Division, and Reproduction
Cytokinesis in Animal Cells
The cell membrane is drawn in until the cytoplasm is pinched into
two equal parts.
Each part contains its own nucleus and organelles.
Lesson Overview
Cell Growth, Division, and Reproduction
Cytokinesis in Plant Cells
In plants, the cell membrane is not flexible enough to draw inward
because of the rigid cell wall.
Instead, a cell plate forms between the divided nuclei that develops into
cell membranes.
A cell wall then forms in between the two new membranes.
Lesson Overview
Cell Growth, Division, and Reproduction
Lesson Overview
10.3 Regulating
the Cell Cycle
Lesson Overview
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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.
Lesson Overview
Cell Growth, Division, and Reproduction
Lesson Overview
10.4 Cell Differentiation
Lesson Overview
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
Stem Cells and Development
What are stem cells?
The unspecialized cells from which differentiated cells develop are known
as stem cells.
Lesson Overview
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
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
Cell Growth, Division, and Reproduction
Frontiers in Stem Cell Research
What are some possible benefits and issues associated with stem cell
research?
Stem cells offer the potential benefit of using undifferentiated cells to repair
or replace badly damaged cells and tissues.
Human embryonic stem cell research is controversial because the
arguments for it and against it both involve ethical issues of life and death.
Lesson Overview
Cell Growth, Division, and Reproduction
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.
Lesson Overview
Cell Growth, Division, and Reproduction
Ethical Issues
Most techniques for harvesting, or gathering, embryonic stem cells
cause destruction of the embryo.
Government funding of embryonic stem cell research is an important
political issue.
Groups seeking to protect embryos oppose such research as unethical.
Other groups support this research as essential to saving human lives
and so view it as unethical to restrict the research.