CHAPTER 9 CELLULAR REPRODUCTION. 9 Cellular... · RATIO OF SURFACE AREA TO VOLUME The key factor...
Transcript of CHAPTER 9 CELLULAR REPRODUCTION. 9 Cellular... · RATIO OF SURFACE AREA TO VOLUME The key factor...
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.