Transcript Most mammalian cells = 12-24 hours Some bacterial cells = 20

When Would a Cell Divide?
 Growth
 Repair or Replacement
 Cancer
Different cells divide at different rates:
 Most mammalian cells = 12-24 hours
 Some bacterial cells = 20-30 minutes
Interphase
Cell does most of its’ growth during
• During
interphase
interphase a cell
performs all of its
regular functions
and gets ready to
divide
• Metabolic
activity is very
high
Figure 8.5
• Untwisting and replication of DNA: S phase
Figure 10.4B
Chromosomes condense at the start of
mitosis.
• DNA wraps around proteins
(histones) that condense it.
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
Structure of Chromosomes
– Homologous chromosomes are identical pairs of
chromosomes.
– One inherited from mother and one from father
– made up of sister chromatids joined at the
centromere.
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G2 Phase
• This phase spans the
time from the
completion of DNA
synthesis to the onset
of cell division
• Following DNA
replication, the cell
spends about 2-5
hours making proteins
prior to entering the M
phase
Figure 8.5
INTERPHASE
PROPHASE
Centrosomes
(with centriole pairs)
Early mitotic
spindle
Centrosome
Chromatin
Nucleolus Nuclear
envelope
Figure 8.6
Plasma
membrane
Chromosome,
consisting of two
sister chromatids
Fragments
of nuclear
envelope
Centrosome
Kinetochore
Spindle
microtubules
METAPHASE
ANAPHASE
Cleavage
furrow
Metaphase
plate
Spindle
Figure 8.6 (continued)
TELOPHASE AND CYTOKINESIS
Daughter
chromosomes
Nuclear
envelope
forming
Nucleolus
forming
Cytokinesis differs for plant and animal
cells
• In animals, cytokinesis
occurs by cleavage
– This process pinches the
cell apart
– The first sign of cleavage
is the appearance of a
cleavage furrow
Figure 8.7A
Cleavage
furrow
Cleavage
furrow
Contracting ring of
microfilaments
Daughter cells
Cytokinesis differs for plant and animal
cells
– As the daughter
chormosomes move to
opposite poles
– The cytoplasm constricts
along the plane of the
metaphase plate
The process of cytokinesis
divides the cell into two
genetically identical cells
Figure 8.7A
Cleavage
furrow
Cleavage
furrow
Contracting ring of
microfilaments
Daughter cells
Plant Cell Telophase/Cytokinesis
• When the cell
divides, the sister
chromatids separate
Chromosome
duplication
– Two daughter
cells are
produced
Sister
chromatids
Centromere
– Each has a
complete and
identical set of
chromosomes
Chromosome
distribution
to
daughter
cells
Figure 8.4C
When Would a Cell Divide?
 Growth
 Repair or Replacement
 Cancer
Different cells divide at different rates:
 Most mammalian cells = 12-24 hours
 Some bacterial cells = 20-30 minutes
Explain how mitosis ensures that daughter nuclei are genetically identical.
Cells divide at different rates.
• The rate of cell division varies with the need for
those types of cells.
• Some cells are unlikely to divide (G0).
Cell size is limited.
• Volume increases faster than surface area.
• Surface area must allow for
adequate exchange of materials.
– Cell growth is coordinated with
division.
– Cells that must be large have
unique shapes.
It’s too late to apoptise!
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