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CELL CYCLE
Figure 12.0 Mitosis
Figure 12.1a The functions of cell division: Reproduction
Figure 12.1b The functions of cell division: Growth and development
Figure 12.2 Eukaryotic chomosomes
Figure 12.1b The functions of cell division: Growth and development
Mitosis
• The form of cell division by which a
eukaryotic somatic cell duplicates.
• Mitosis is asexual reproduction.
• Cell division is the continuation of
life based on the reproduction of
cells.
Mitosis
Skin Cell
Skin Cell
2n=46
2n=46
2n=46
two
identical
daughter
cells
Skin Cell
Somatic Reproduction
• Most eukaryotic cells reproduce
asexually by mitosis.
• Somatic cells are all body cells
(like nerve, liver, etc...) except
sperm and ova (egg).
• All Somatic cells have the same
number of chromosomes.
Cell Cycle
• The dividing and non-dividing
stages in the life of a cell.
• Phases:
1. Interphase: growth and DNA
replication
2. Prophase
3. Metaphase
Mitotic division
4. Anaphase
5. Telophase
Cell Cycle
S
phase
G1
interphase
Mitosis
-prophase
-metaphase
-anaphase
-telophase
G2
Figure 12.14 Molecular control of the cell cycle at the G2 checkpoint
Interphase
• Comprises about 90% of the cell
cycle.
• Cellular growth:
a. protein synthesis
b. metabolic activities
c. DNA synthesis
• Made up of three phases:
1. G1 phase
2. S phase
3. G2 phase
Interphase
G1 (gap) phase:
a. Cellular growth, protein synthesis
and metabolic activities.
2. S phase:
a. DNA replication takes place.
3. G2 (gap) phase:
a. organelles replicated,
chromosomes condense,
microtubules assemble
a. Preparation for M phase.
1.
Interphase
• Nucleus and nucleolus visible.
chromatin
Nuclear
membrane
cell membrane
nucleolus
Question:
• What is a chromosome?
Answer:
• A chromosome is made up of
a DNA - histone protein
complex called chromatin.
Chromatin is a long, thin fiber
that is folded and coiled to
form chromosomes. DNA double helix
Histone
proteins
chromosome
Question:
• What is a replicated
chromosome?
Answer:
• A replicated chromosome consist
of two strands of identical
chromosomal material called
chromatids (sister chromatids).
chromosome
S phase: chromosomes replicate
chromatid
chromosome
chromatid
centromere
Chromosome duplication and distribution
during mitosis
Question:
• When is a chromatid a
chromatid?
• A chromatid is a chromatid as
long as it is held in
association with a sister
chromatid at the centromere.
centromere
Chromatid
chromosome
chromatid
Mitotic Phase
• Mitosis
a. nuclear division of genetic
material.
b. prophase-metaphaseanaphase-telophase
• Cytokinesis
a. cytoplasmic division.
b. Indicator of telophase.
Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase;
prometaphase
Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase;
anaphase; telophase and cytokinesis.
Mitosis
Prophase
• Longest phase
• Nucleolus disappears
• Chromatin material condenses
into chromosomes, consisting
of two sister chromatids.
Prophase
• Centrioles move apart (not found
in plants).
• Spindle fibers form and attach
from centrioles to centromeres
by kinetochores.
• Nuclear envelope fragments and
disappears.
Prophase
early prophase
late prophase
centrioles
spindle fibers
aster
fibers
nuclear envelope
disappearing
centromere
Question:
• What attaches the spindle
fibers to the centromeres?
Answer: Kinetochores
aster
fibers
centromere
centriole
spindle fiber
sister
chromatid
kinetochores
sister
chromatid
Metaphase
• Shortest phase
• Centrioles are at opposite
ends of the cell and attached
with aster fibers.
• Chromosomes move to the
metaphase plate (equatorial
plate - center of cell).
Metaphase
centrioles
aster
fibers
spindle fibers
metaphase plate
Metaphase
Anaphase
• Centromeres uncouple and
spindle fibers shorten.
• Sister chromatids separate
and move apart.
• After separation, chromatids
are now considered
chromosomes.
Anaphase
• During this phase, the cell contains
twice the normal number of
chromosomes.
• Cell begins to elongate.
• At the end, there are equal numbers of
chromosomes at the poles.
Anaphase
No longer sister chromatids,
now chromosomes
aster
fibers
spindle fibers
centrioles
Telophase
• Cleavage furrow develops in
animal cells (Cytokinesis
begins).
• Cell plate develops in plants (no
cleavage furrows in plants).
• Nucleolus reappears.
cell plate
Telophase
• Nuclear membrane reappears.
• Chromosomes uncoil.
• In the end, two genetically
identical nuclei (karyokinesis
completed) are present.
Telophase
cleavage furrow (cytokinesis)
nuclear membrane reforming
nucleolus reappears
Cytokinesis
• Cytoplasmic division
• Cell plate complete in plants
• In the end, two separate daughter
cells produced with single nucleus.
cell plate
Cytokinesis in Animal and Plant
Cells
Mitosis in a Plant Cell
Mitosis in an Onion Root
Question:
• A cell containing 20
chromosomes at the
beginning of mitosis would, at
its completion, produce cells
containing how many
chromosomes each?
Answer:
• 20 chromosomes
Question:
• A cell containing 40
chromatids at the beginning of
mitosis would, at its
completion, produce cells
containing how many
chromosomes each?
Answer:
• 20 chromosomes
Bacterial Cell Division (Binary Fission)
Density-dependent Inhibition of Cell Division
Breast Cancer Cell
Mammogram:normal (left) and cancerous (rt)
Cancer Cells
Cancer Cells Versus
Normal Cells
1)Give two reasons why cells divide.
2) As a cell increases in size, which
increases more rapidly, its surface
area or its volume?