CHAPTER 9 CELLULAR REPRODUCTION P. 243-257

SECTION 9-1 CELLULAR GROWTH Page 244

ESSENTIAL QUESTION

 Why is it beneficial for cells to remain small?

MAIN IDEA  Cells grow until they reach their size

limit, then they either stop growing or divide.

CELL SIZE LIMITATIONS  Most cells are smaller than a period at

the end of a sentence.  There are two reasons cells divide rather

that continue to grow.  The larger the cell becomes, the more

demands the cell places on it DNA.  The larger the cell becomes, the more

trouble the cell has moving nutrients and wastes across the cell membrane.

HOW DOES THE AMOUNT OF SURFACE AREA CHANGE AS THE CELL’S VOLUME INCREASES?

RATIO OF SURFACE AREA TO VOLUME

 The key factor that limits the size of a cell is the ratio of its surface area to volume.  The surface area refers to the area

covered by the plasma membrane.  The volume refers to the space taken by

the inner contents of the cell, including the organelles in the cytoplasm and the nucleus.

HOW DOES THE AMOUNT OF SURFACE AREA CHANGE AS THE CELL’S VOLUME INCREASES?

RATIO OF SURFACE AREA TO VOLUME

 As a cell grows in size, its volume increases faster than its surface area.

 This means the cell might have trouble supplying and transporting nutrients and expelling enough waste products.

 By remaining small, cells can sustain themselves more easily.

CELL CYCLE  Once a cell reaches its size limit, it will

either stop growing or divide.  Most cells divide. Nerve and muscle cells

do not divide.  Cell division also is the way the cell

reproduces so that you grow and heal certain injuries.

 Cells reproduce by a cycle of growing and dividing called the cell cycle.

CELL CYCLE   3 main stages……..

  Interphase – cell grows, carries out certain cellular functions, replicates its DNA [3 substages]

  Mitosis – cell’s nucleus and nuclear material, DNA, divide [4 substages]

  Cytokinesis – cytoplasm divides

CELL CYCLE

STAGES OF INTERPHASE  G1 stage (normal cell growth) has the

longest duration.  G1 - 1st stage, a cell is growing, carrying

out normal cell functions, and preparing to replicate or copy DNA

 S - 2nd stage, cell copies its DNA in preparation for cell division  Chromosomes contain the genetic

material that is passed from one generation to the next.

STAGES OF INTERPHASE  Chromatin is the relaxed form of DNA

in a cell’s nucleus.  Chromatin condenses or tightens to

form chromosomes.  G2 - 3rd stage, Cell prepares for the

division of its nucleus.  The cell makes sure everything is ready

for mitosis.  A cell spends the majority of its

lifetime in interphase.

SECTION 9-2 MITOSIS AND CYTOKINESIS Page 248

MAIN IDEA  Eukaryotic cells reproduce by mitosis, the

process of nuclear division, and cytokinesis, the process of cytoplasmic division.

MITOSIS AND CYTOKINESIS

PHASES OF MITOSIS - PROPHASE

 1st phase - longest  Chromatin tightens into chromosomes

that are X-shaped and become visible.  Centrioles separate and move to opposite

poles of the cell.  Nuclear membrane disintegrates.  Nucleolus disappears.  Mitotic spindle begins to form between

the poles.

CHROMOSOMES

PROPHASE

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PROPHASE  Spindle apparatus is made of spindle

fibers, centrioles, and aster fibers.  The spindle apparatus is important

in organizing and moving chromosomes before cell division.

 Plant cells do not have centrioles.

BY THE END OF PROPHASE, THE FOLLOWING HAS OCCURRED:

 By the end of prophase, the following has occurred:  Nuclear envelope seems to disappear.  Spindle fibers attach to sister

chromatids on both sides of the centromere.

METAPHASE  2nd phase - shortest  Sister chromatids are pulled along the

spindle apparatus to center of cell and line up in the middle.

 Tension of spindle fibers pulls them along.

METAPHASE

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ANAPHASE  3rd phase  The centromeres that join the sister

chromatids split.  The sister chromosomes become

individual chromosomes.  The two sets of chromosomes move

apart to opposite poles.

ANAPHASE

TELOPHASE  4th phase - last phase  Chromosomes gather at opposite

ends of the cell and lose their shape.  Two new nuclear envelopes form.  Nucleoli reappear.  Spindle apparatus comes apart.

TELOPHASE

CYTOKINESIS  Cytokinesis usually happens at the same

time as telophase.  The cell membrane is pulled inward until

the cytoplasm is pinched into two nearly equal parts.

 Results are two cells, with identical nuclei.

 In plant cells, a cell plate forms that later becomes cell wall to divide the cells.

CYTOKINESIS

SECTION 9-3 CELL CYCLE REGULATION Page 253

MAIN IDEA  The normal cell cycle is regulated by

cyclin proteins.

CYCLINS  In a multicellular organism, cell growth

and cell division are carefully controlled.  When an injury such as a cut in the skin

occurs, cells at the edge of the cut divide rapidly.

 When the healing process is nearly complete, the rate of cell division slows and then returns to normal.

CYCLINS  When cells come into contact with one

another, molecules on their surface signal them to stop growing.

 Cyclins, a group of proteins, regulate the timing of the cell cycle in eukaryotic cells.

 Cyclins are one group of proteins involved in cell cycle regulation.

 Other proteins, called regulatory proteins, regulate the cell cycle in different ways.

CANCER  Contols on cell growth can be turned on

and off by the body.  Cancer is a disorder in which some of the

body’s cells lose the ability to control growth.

 Cancer cells do not respond to the signals that control the growth of most cells.

 As a result, cancer cells divide uncontrollably.

CANCER  Cancer cells reproduce rapidly because

they spend less time in interphase.  Cancer cells do not stop growing when

they touch other cells.  They continue to grow and divide until

their supply of nutrients is used up.

CANCER CAN BE CAUSED BY….

 Changes that occur in the regulation of cell growth and division of cancer cells are due to mutations or changes in segments of DNA.

 The changes can damage the control of the proteins that regulate the cell cycle.

 The genetic change or damage can often be repaired by various repair systems

 If repair systems fail, cancer can result.

CARCINOGENS  Various environmental factors can affect

the occurrence of cancer cells.  Substances that are known to cause

cancer are called carcinogens.  Examples: cigarettes, asbestos, X rays,

the Sun’s ultraviolet rays

APOPTOSIS  Apoptosis is programmed cell death.  Cells going through apoptosis actually

shrink and shrivel in a controlled process.

 Example: When hands and feet begin to develop, there are cells between fingers and toes that look like webbing.

 The webbing is not present in the mature organism.

STEM CELLS  Most cells in a nulticellular organism are

designed for a specialized function.  Stem cells are unspecialized cells that

can develop into specialized cells when under the right conditions.

 Two basic types of stem cells:  Embryonic- After a sperm terilizes an

egg, the resulting mass of cells divides until there are about 100-150 cells.

STEM CELLS  Adult- Found in various tissues in the

body and might be used to maintain and repair the same kind of tissue where they are found.

 Researchers think certain kinds of adult stem cells might be able to develop into different kinds of cells for treatment of disease and conditions.