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Biology is the only subject in
which multiplication is the same
thing as division…
Regents Biology
2006-2007
MITOSIS:
Making New Cells
Making New DNA
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Where it all began…
You started as a cell smaller than
a period at the end of a sentence…
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And now look at you…
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How did you
get from there
to here?
Getting from there to here…
 Going from egg to baby….
the original fertilized egg (zygote) has to
divide…
and divide…
and divide…
and divide…
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Binary fission
Why do cells divide…
 One-celled organisms


for reproduction
asexual reproduction (clones)
amoeba
 Multi-celled organisms

for growth & development
 from fertilized egg to adult

for repair & replacement
 replace cells that die from
normal wear & tear or from injury
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starfish
regeneration
Examples of Asexual Reproduction
 Binary Fission is the equal
division of both the organism’s
cytoplasm and nucleus to form
two identical organisms
 Budding involves one parent
dividing its nucleus (genetic
material) equally, but cytoplasm
unequally
yeast
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protist
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 Sporulation (spore formation) reproduction
involving specialized single cells coming
from one parent
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Regeneration
 Grafting
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Asexual Reproduction
 Advantages
Genetic continuity
 Faster
 Do not need a mate

 Disadvantages
If environmental conditions change, may
die out
 Disease could eliminate the population

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Dividing cells…
 What has to be copied
DNA
 organelles
 cell membrane
 lots of other
molecules

 enzymes
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plant cell
animal cell
Copying DNA
 A dividing cell duplicates its DNA
creates 2 copies of all DNA
 separates the 2 copies to opposite ends
of the cell
 splits into 2 daughter cells

DNA
cell
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nucleus
 But the DNA starts
loosely wound in
the nucleus
 If you tried to divide
it like that, it could
tangle & break
Organizing & packaging DNA
DNA
(chromatin)
cell
nucleus
DNA has been
“wound up”
DNA in chromosomes in
everyday “working” cell
cell
nucleus
4 chromosomes
in
thisBiology
organism
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DNA in chromosomes in cell
getting ready to divide
Chromosomes of Human Female
46 chromosomes
23 pairs
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Chromosomes of Human Male
46 chromosomes
23 pairs
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Copying & packaging DNA
 When cell is ready to divide…
copy DNA first, then…
 coil up doubled chromosomes
like thread on a spool…

 now can move DNA around cell without having it
tangle & break
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Copying DNA
Coil DNA into
compact chromosomes
What happens when DNA breaks?
 Mutations which can lead to……..
 Cancer – uncontrolled cell growth
melanoma
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double-stranded
human chromosomes
ready for mitosis
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DNA must be duplicated…
chromosomes in cell
DNA in chromosomes
cell
nucleus
4 single-stranded chromosomes
duplicated chromosomes
duplicated
chromosomes
Biology chromosomes
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double-stranded
cell
nucleus
INTERPHASE
 CELL IS
GROWING
 CHROMOSOMES
ARE REPLICATED
(COPIED)
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PROPHASE
1. CHROMATIN BECOMES
2.
3.
4.
5.
6.
CONDENSED (THICKER)
NUCLEOLUS DISAPPEARS
NUCLEAR MEMBRANE
DISAPPEARS
CENTRIOLES BEGIN TO
MOVE TOWARDS THE
POLES
SPINDLE FIBERS START
TO APPEAR
CHROMOSOMES BECOME
VISIBLE
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METAPHASE
 CHROMOSOMES LINE UP
ALONG THE MIDDLE OF
CELL
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ANAPHASE
 CENTROMERES

SPLIT ALLOWING
CHROMATIDS TO
SEPARATE
ONE MATCHING
CHROMATID
MOVES TO EACH
POLE
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TELOPHASE AND
CYTOKINESIS
 CHROMATIDS AT
OPPOSITE POLES
 SPINDLE FIBERS
DISAPPEAR
 NUCLEAR
MEMBRANE
REAPPEARS
 CYTOKINESIS:
CELL DIVIDES INTO
TWO
GENETICALLY
IDENTICAL CELLS
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New “daughter” cells
 Get 2 exact copies of original cells
same DNA
 “clones”

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Cell division in Animals
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Mitosis in whitefish embryo
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onion root tip
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KEYS TO MITOSIS
 Original cell has complete set of chromosomes

This is known as DIPLOID or 2N

No genetic material exchanged
Cells are GENETICALLY IDENTICAL
Daughter Cells are also DIPLOID or 2N
 One division results in 2 DAUGHTER CELLS


 Ex. Original cell has 46 chromosomes, daughter cells will have
46 chromosomes
 IN SINGLE CELLED ORGANISMS:

Method of reproduction (ASEXUAL)
 Protists, some Algae, and Molds
 IN MULTI-CELLED ORGANISMS:

Mitosis used for GROWTH and REPLACEMENT of
BODY CELLS (skin, liver, heart etc…)
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Overview of mitosis
interphase
I.P.M.A.T.C.
prophase
Please Make Another Two Cells
cytokinesis
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metaphase
anaphase
telophase
Basic diagram of mitosis
HUMAN SKIN
CELL
46
Chromosomes
46
Chromosomes
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2 NEW
HUMAN
SKIN
CELLS
46
Chromosomes