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Mitosis
Cellular Reproduction
The Cell Cycle
• Your cells are always doing something,
which is what is described by the cell
cycle.
• Sometimes, they are growing, making
proteins, doing chemical reactions, and
maintaining homeostasis.
• Other times, they are dividing to make
more cells.
• These are the 2 main parts of the cell
cycle.
2 parts of the Cell Cycle
• During interphase, the cell
grows and carries on
normal cell functions.
More than 95% of the
time, this is what your
cells are doing.
• Once in while, your cells
divide in half to make
more cells. We call this
mitosis.
Mitosis: key facts
• The definition of mitosis is the period of time when
the cell’s nucleus divides to create 2 identical
daughter cells.
Mitosis: key facts
• Mitosis only happens in body
cells, which are called somatic
cells (not reproductive cells).
• Mitosis occurs in eukaryotes:
plants, animals, and people.
• Mitosis produces diploid cells
(that have 23 pairs of
chromosomes)
Mitosis: Key facts
• 1 cell divides in half to form 2
new cells, called daughter cells.
• These cells are identical to the
parent cells, and are called
daughter cells.
• Single celled eukaryotes can
reproduce this way: asexually (all
by themselves)
Interphase
• Interphase comes before mitosis.
• During interphase, the cell makes a copy of its
DNA, so that it is ready to divide.
• Over 95% of the time, cells are in interphase.
• Now, the cell is ready to divide in the 5 step process
of mitosis!
Vocabulary preparation
• A duplicated chromosome looks like the
letter X and each half is called a “sister
chromatid.”
• The sister chromatids are held together in
the center by the centromere.
Prophase: Phase 1
• The longest phase of
mitosis.
• Chromosomes come
together (condense) are
become visible under
the microscope.
• The nuclear membrane
begins to dissolve.
Metaphase: Phase 2
• Chromosomes line up in the center of the cell.
• Centromeres attach to spindle fibers which help
them move around the cell.
Anaphase:
rd
3
• Sister chromatids begin to pull
apart at the centromere.
• Sister chromatids begin to
move to the opposite sides of
the cell.
• Chromosomes don’t look like
Xs anymore, now they are
chromatids.
phase
Telophase: Phase 4
• In telophase, the now separated
chromatids reach the opposite
sides of the cell.
• Chromosomes start to unwind,
and you can’t see them under the
microscope anymore.
• The nuclear membrane re-forms.
Now the cell has 2 brand new
nuclei, and begins to separate into
2 cells.
Cytokinesis: after mitosis
• Now the cell’s cytoplasm
divides, so 2 new cells with 2
new nuclei are formed.
• In animals, cells pinch apart
along a seam called the
cleavage furrow.
• In plants, cells form a new
cell wall in between the 2
nuclei called the cell plate.
Why do cells do mitosis?
• There are many reasons why cells go through
mitosis:
• Reproduction in single celled eukaryotes
• Helps us grow bigger and taller
• Helps repair wounds
• Helps fetuses turn cells into tissues into organs into
organ systems (development)