Transcript The Cell Cycle

Unit
Cell Cycle & Mitosis
Cell reproduction in multicellular
and unicellular organisms

Unicellular: reproduce by
binary fission, asexual
reproduction

Multicellular: reproduce
by cell division; process
of growth and repair
depend on cell division;
also involves the
production of sex cells
Describe chromosomes
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Animation:
http://www.johnkyrk.com/chromoso
mestructure.html
Carriers of genetic
material found in
nucleus
Made up of DNA
Information is copied
and passed to future
generations
Usually DNA exists as
chromatin which are
long, winding strands
that condense into
chromosomes before
dividing
Chromosome structure

Chromosomes are
made up of two
chromatids which are
held together with a
centromere

Human chromosome
number is 46 in body
cells; 23 in sex cells
Describe the cell cycle
Sequence of growth and division in
the cell
 Consists of 4 phases:
1. M phase: cell division (mitosis)
2. S phase: copying of
chromosomes
3. G1 phase: growth phase
4. G2 phase: growth phase
 Interphase is the growth period
where DNA is copied; includes S,
G1 and G2
 Mitosis: dividing period producing
two new cells; includes M phase

List and describe the steps of
mitosis

Mitosis is the division
of cells producing two
cells with the same
number of
chromosomes
Prophase
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Longest phase of mitosis
Chromatin coils into
chromosomes
The nucleus disappears
Centrioles form and move
to opposite poles of cell
Spindle fibers form from
centrioles and begins to
cross cell
Metaphase
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Chromosomes line up
in the middle of the
cell
Spindle now forms
across the cell
Anaphase
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Spindle fibers begin
to shorten
This pulls
chromosomes apart
Now the chromosome
halves are referred to
as chromatids
Telophase
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Chromatids reach
poles
Chromosomes
unwind into chromatin
Spindle fibers break
down
Nucleolus and nuclei
reform
Plasma membrane
begins to pinch in
Cytokinesis
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Division of cytoplasm
In animal cells: cell
membrane continues to
pinch in until two cells are
formed
In plant cells: cell plate
forms in center of cell and
eventually splits cells
At the end of mitosis, two
new cells are produced;
called “daughter” cells
Animation:
http://www.johnkyrk.com/mitosis.html