Download Cells need to divide (reproduce)

Organisms reproduce like offspring.
There are two types of reproduction:
ASEXUAL REPRODUCTION - producing offspring
from only 1 parent
• offspring look EXACTLY like parent
• this type of reproduction is best suited for a
stable environment
• occurs in unicellular organisms and some plants
SEXUAL REPRODUCTION - producing offspring
from two parents
• offspring have characteristics from BOTH parents
• this type of reproduction is suited for either a
stable environment OR
a changing environment
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Cells are organisms. They must reproduce.
• Cells need to divide (reproduce) for ...
growth
healing and repair
to replace dead or damaged cells
• New cells formed must be IDENTICAL to original cells
WHY ?
• So the new cells can perform the same
function as the original cell !
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•• MITOSIS - the process cells use to make exact copies of the cell
(aka - Nuclear Reproduction)
• In order for the cells made by mitosis to be identical,
they must have the same DNA !
• Mitosis is a process that makes sure each cell gets the same DNA !
• Mitosis occurs in SOMATIC CELLS (body cells)
ex) liver cells, skin cells, lung cells
• Somatic cells are DIPLOID (having the total number of chromosomes)
Human diploid number = 46
• Mitosis begins w/ ONE diploid somatic cell
• Mitosis ends w/ TWO diploid somatic cells that are identical !
• It is important that the cells made during Mitosis are identical so that
the new cells made will do the same functions as the original cell !
The Cell Cycle
• The cell cycle is the series of events a cell goes through
during its lifetime
• It includes 3 main parts : Interphase (G1, S phase, and G2),
Mitosis, and Cytokinesis.
• The following is a description of the events that occur
during the cell cycle.
http://www.iknow.net/CDROMs/cell_cdrom/cell3.html
Interphase
(not actually part of Mitosis, but included in the Cell Cycle)
• G1 - Cell is doing
what cell normally
does (performing cell
functions)
• S phase - DNA
Replication occurs
• G2 - Cell prepares to
divide (organelles are
doubled in numbers)
Prophase
• Chromatin condenses into
chromosomes
Sister chromatids are exact
centromere copies of a chromosome.
The centromere is a belt-like
structure that holds sister
chromatids together.
Sister chromatids
• Nuclear membrane
disappears
• Centrioles begin to move
to opposite ends of cell
(aster begins to form)
Metaphase
• Sister chromatids line
up along center
(middle) of cell
• Spindle fibers attach
to each centromere
Anaphase
• Spindle fibers shorten
• Each centromere
breaks apart
• One member of each
sister chromatid pair is
pulled toward each
end of the cell
Telophase
• Nuclear membranes
form around each set
of chromosomes
• Chromosomes uncoil
into chromatin
• The cell now has 2
nuclei and is ready to
divide
Cytokinesis
• The cell divides to form
two identical cells
• Occurs after telophase
• CYTOKINESIS - the
actual, physical division of
one cell into two cells
• Cytokinesis is different in
plants and animals (due to
plants having a cell wall)
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