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Mitosis and Cell Division
Bio 11
August 31, 2007
Cells are extremely small
• Size limit of cells
determined by
area/volume ratio
• Large living things are
made of multiple cells
• Living things divide
cells in order to grow
Living things are extremely
complex
• Cellular machinery is
sophisticated and
required for life
• Blueprints for all
cellular machinery are
contained in genes
• Genes are inherited
from parents
• Humans have
~30,000 genes
All cells require a copy of the
genome
• Genome- all the DNA
of the cell
• Gene- the genetic
information to produce
a single product
(protein)
• DNA replication
copies all cellular DNA
Prokaryotic genomes consist of a
single circular chromsome
• Chromosome- a
single molecule of
DNA
Prokaryotic cells reproduce by
binary fission
1. DNA is copied
2. Copies migrate to
opposite ends of cell
3. Cell membrane/cell
wall pinches off to
form two cells
4. Each daughter cell
has exactly the
same DNA as the
parent cell
Eukaryotic cells have multiple
linear chromosomes
• Eukaryotic chromosome
= DNA + extra proteins
• Chromosomal proteins
assist in DNA compaction
• Each chromosome
contains different genes
• Chromosomes not always
condensed like this
• Chromatin –
uncondensed
chromosomal DNA
Eukaryotic chromsomes are
generally found in pairs
• Chromosomes are
organized and
numbered by size
• Humans: 2 x 23
homologous pairs
of chromosomes =
46 total
chromosomes
Chromosome structure
• Decondensed
chromosome- chromatin
• After copying, chromosome
consists of two sister
chromatids, joined at the
centromere
• Kinetochore – proteins
found on surface of
centromere
Each chromosome must be copied
before cells can divide
• Called “chromosome”
at all stage
• Sister chromatids
contain identical DNA
Mitosis vs. Meiosis
• Mitosis – asexual cellular reproduction (somatic
cells)
– Allows multicellular organisms to grow
– Daughter cells are identical to parent cell
• Meiosis – cell division for formation of gametes
(eggs and sperm)
– Allows sexual reproduction to generate species
diversity
– Daughter cells have half the genetic information as
parent cell
The Cell Cycle
• G1 – “Growth 1” or “Gap
1” – cell growth
• S phase – DNA synthesis
• G2 – interval of rest
before cell division
• M – mitosis
• Cytokinesis – splitting of
cell contents
• GO – A state of nondivision
LE 8-5
INTERPHASE
S
(DNA synthesis)
G1
G2
Mitosis
• The sorting and separation of
chromosomes in nucleus somatic
eukaryotic cells during cell division
• Forms 2 identical daughter cells (1/2 size)
• For growth/replacement/healing
• Associated with cancer
• In humans: ~25 million/sec.
• Divided into phases
Phases of Mitosis
•
•
•
•
Prophase*
Metaphase
Anaphase
Telophase
* Campbell text adds “prometaphase”
• Interphase – time in between mitotic phases
– Normal cell functions (G1+S+G2)
• Cytokinesis- divides cytosol/organelles (creates
daughter cells)
Peripheral elements of Mitosis
• Centrosomes (2) – form spindle fibers, and
consist (in animal cells) of 2 centrioles
• Spindle fibers – made of microtubules,
they pull apart sister chromatids of
chromosomes
LE 8-6a
INTERPHASE
Centrosomes
(with centriole pairs)
Nucleolus
Nuclear
envelope
PROPHASE
Chromatin
Plasma
membrane
Early mitotic
spindle
PROMETAPHASE
Centrosome
Chromosome, consisting
of two sister chromatids
Centromere
Fragments
of nuclear
envelope
Kinetochore
Spindle
microtubules
LE 8-6b
METAPHASE
ANAPHASE
Cleavage
furrow
Metaphase
plate
Spindle
TELOPHASE AND CYTOKINESIS
Daughter
chromosomes
Nuclear
envelope
forming
Nucleolus
forming
Cytokinesis in animal cells is
different from plant cells
• Actin and myosin
filaments work to
contract cell in center
• Cell furrow is formed
Plant cell walls aren’t flexible
• Vesicles containing
cellulose form in
center of cell
• Fusion of vesicles
forms cell plate
• Cell plate forms cell
wall of new cells
Control of the mitotic cycle is critical
G1 checkpoint
G0
G1
Control
system
S
G2
M
M checkpoint
G2 checkpoint
External signals can activate or
deactivate the cell cycle
• Signals include
hormones, growth
factors
• Contact inhibition,
density inhibition,
anchorage
dependence are
important signals
LE 8-8a
Cells anchor to
dish surface
and divide.
When cells have
formed a complete
single layer, they
stop dividing
(density-dependent
Inhibition).
If some cells are
scraped away, the
remaining cells
divide to fill the dish
with a single layer
and then stop
(density-dependent
inhibition).
LE 8-8aa
Cells anchor to
dish surface
and divide.
When cells have
formed a complete
single layer, they
stop dividing
(density-dependent
inhibition).
LE 8-8ab
If some cells are
scraped away, the
remaining cells
divide to fill the dish
with a single layer
and then stop
(density-dependent
inhibition).
LE 8-8b
After forming a
single layer,
cells have
stopped dividing.
Providing an
additional supply of
growth factors
stimulates
further cell division.
LE 8-10
Lymph
vessels
Tumor
Blood
vessel
Glandular
tissue
A tumor grows from a
single cancer cell.
Cancer cells invade
Neighboring tissue.
Cancer cells spread through
lymph and blood vessels to
other parts of the body.
LE 8-10a
Tumor
Glandular
tissue
A tumor grows from a
single cancer cell.
Cancer cells invade
neighboring tissue.
LE 8-10b
Lymph
vessels
Blood
vessel
Cancer cells invade
neighboring tissue.
Cancer cells spread through
lymph and blood vessels to
other parts of the body.
Figure 8.11A
Figure 8.11B
Figure 8.11C
LE 8-12
Chromosomes
Centromere
Sister chromatids
LE 8-13
Haploid gametes (n = 23)
n
Egg cell
n
Sperm cell
Meiosis
Fertilization
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
Mitosis and
development
2n
LE 8-14a
MEIOSIS I : Homologous chromosome separate
INTERPHASE
PROPHASE I
METAPHASE I
ANAPHASE I
Centrosomes
(with centriole
pairs)
Microtubules
Sister chromatids
Sites of crossing over attached to Metaphase remain attached
plate
kinetochore
Spindle
Nuclear
envelope
Sister
chromatids
Chromatin
Tetrad Centromere
(with kinetochore)
Homologous
chromosomes separate
LE 8-14b
MEIOSIS II : Sister chromatids separate
TELOPHASE I
AND CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
AND CYTOKINESIS
Cleavage
furrow
Sister chromatids
separate
Haploid daughter
cells forming