Lesson Overview

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Lesson Overview

• 10.1 Cell Growth, Division, and Reproduction

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Information Overload

• Living cells store critical information in DNA.
• As a cell grows, that information is used to
  build the molecules needed for cell growth.
• As size increases, the demands on that
  information grow as well. If a cell were to grow
  without limit, an information crisis would
  occur.

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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.

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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
  cells volume.
• The ratio of surface area to volume is key to
  understanding why cells must divide as they grow.

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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.
• As a cell becomes larger its volume increases
  faster than its surface area.
• 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.

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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.

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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.

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Asexual Reproduction

• In multicellular organisms, cell division leads
  to growth. It also enables an organism to repair
  and maintain its body.
• In single-celled organisms, cell division is a
  form of reproduction.

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Asexual Reproduction

• Asexual reproduction is reproduction that
  involves a single parent producing an offspring.
  The offspring produced are, in most cases,
  genetically identical to the single cell that
  produced them.
• Asexual reproduction is a simple, efficient, and
  effective way for an organism to produce a large
  number of offspring.
• Both prokaryotic and eukaryotic single-celled
  organisms and many multicellular organisms can
  reproduce asexually.

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Examples of Asexual Reproduction

• Bacteria reproduce by binary fission.
• Starfish can reproduce by fragmentation.
• Hydras reproduce by budding.

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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.

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Comparing Sexual and Asexual Reproduction
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Lesson Overview

• 10.2 The Process of Cell Division

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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.

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Prokaryotic Chromosomes

• Prokaryotic cells lack nuclei. Instead, their
  DNA molecules are found in the cytoplasm.
• Most prokaryotes contain a single, circular DNA
  molecule, or chromosome, that contains most of
  the cells genetic information.

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The Prokaryotic Cell Cycle

• The prokaryotic cell cycle is a regular pattern
  of growth, DNA replication, and cell division.
• Most prokaryotic cells begin to replicate, or
  copy, their DNA once they have grown to a certain
  size.
• When DNA replication is complete, the cells
  divide through a process known as binary fission.

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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.

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The Eukaryotic Cell Cycle

• The eukaryotic cell cycle consists of four
  phases G1, S, G2, and M.
• Interphase is the time between cell divisions.
  It is a period of growth that consists of the G1,
  S, and G2 phases. The M phase is the period of
  cell division.

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G1 Phase Cell Growth

• In the G1 phase, cells increase in size and
  synthesize new proteins and organelles.

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S Phase DNA Replication

• In the S (or synthesis) phase, new DNA is
  synthesized when the chromosomes are replicated.

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G2 Phase Preparing for Cell Division

• In the G2 phase, many of the organelles and
  molecules required for cell division are produced.

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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.

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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

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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.

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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.

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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.

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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.

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Cytokinesis

• Cytokinesis is the division of the cytoplasm.
• The process of cytokinesis is different in
  animal and plant cells.

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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.

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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.

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Lesson Overview

• 10.3 Regulating the Cell Cycle

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Controls on Cell Division

• How is the cell cycle regulated?
• The cell cycle is controlled by regulatory
  proteins both inside and outside the cell.

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• 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.

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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.

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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.

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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.

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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.

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• 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.

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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.
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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.

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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.

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Lesson Overview

• 10.4 Cell Differentiation

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THINK ABOUT IT

• The human body contains hundreds of different
  cell types, and every one of them develops from
  the single cell that starts the process. How do
  the cells get to be so different from each other?

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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.

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From One Cell to Many

• 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.

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From One Cell to Many

• During development, an organisms cells become
  more differentiated and specialized for
  particular functions.
• For example, a plant has specialized cells in
  its roots, stems, and leaves.

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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.

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Mapping Differentiation

• In some organisms, a cells 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.

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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.

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Stem Cells and Development

• What are stem cells?
• The unspecialized cells from which
  differentiated cells develop are known as stem
  cells.

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• 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.

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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.

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Stem Cells

• Stem cells are unspecialized cells from which
  differentiated cells develop.
• There are two types of stem cells embryonic and
  adult stem cells.

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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.

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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.

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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.

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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.

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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.