Transcript Chapter 10: Cell Division & Mitosis

Chapter 10: Cell Division &
Mitosis
Mitosis
• Division of cell nucleus
• Common to ALL living things-- but details
of mitosis vary from organism to organism
• The sequence of phases is fixed in all
organisms, but time spent in each phase
varies
Biologists Compare Cell Division
1) In different organisms by comparing their
cell cycles
2) Between different kinds of tissues within
the animal/plant
3) Between normal tissue and tissue repair
after injury
4) Between the young child and elderly
person
Biologists Compare Cell Division cont.
5) Between embryological (unspecialized
cells) and in fetal cells that develop into
tissues (specialized cells)
6) Between prokaryotic and eukaryotic cells
- Prokaryotic & some protists binary
fission
7) Between cancer and normal cells
Cell Division in Eukaryotes
1) Unicellular organisms– cell division 
new individuals (reproduction)
2) Multicellular organisms-- cell growth/
repair/ maintenance/ reproduction
a. Plants- formation of roots, stems, leaves
b. Animals- formation of specialized cells (nerve,
bone, muscle)– blood and skin cells are
replaced as needed throughout life (106 mitotic
cell division/sec)
Cell Division in Eukaryotes cont.
3) In all cell divisions there is chromosome
replication/ duplication
- Body/ somatic cells= 46
chromosomes (23 pairs/
1 set from each parent)
- Gametes/ sex cells= 23
chromosomes (1 set from
parent)
Controls of Cell Division ( Cell Cycle)
1) Rate varies between species and between tissues within
same organism-anywhere from min/hr/day/never
a. Go Phase
• Cells never leave G1 phase
• In this way, specialized cells remain very active-never having to stop working to divide; all energy is
used to carry out important specialized functions
Ex: Nerve and muscle cells (can enlarge through use of
anabolic steroids), Heart cells (can enlarge in
athletes), Leaf cells (palisade, xylem, phloem), Red
blood cells (in circulation) complete cycle only in
growth tissues
Controls of Cell Division ( Cell Cycle) cont.
b. Some cells divide very rapidly
Ex: Bacteria E. coli (prokaryote- every
30 min)
Skin and blood (106 div/sec)
Digestive tract (6 hrs)
Respiratory tract (8 hrs)
Controls of Cell Division ( Cell Cycle) cont.
2) Could be caused by some “trigger
protein”-- some molecular on/off switch
like a hormone of an enzyme
- Turned on rapidly in times of cell stress
or gradually increases during G1 phase to
a level when S phase can begin
Controls of Cell Division ( Cell Cycle) cont.
3) Or by special regions called TELOMERES-found at the ends of chromosomes
- These telomeres shorten with every
subsequent division until division stops
a. Changes seen in normal/ cancer cells
b. Changes seen in early aging (Progeria)/
normal
Overview of Cell Cycle
Phases of Cell Cycle
• Sequence is fixed from start to finish (for
entire life cycle)
a. Interphase (non-dividing cells) has 3 distinct
phases: G1, S, G2
b. Mitosis (dividing cells) has 4 phases in
nucleus: P, M, A, T
c. Cytokinesis: C
Phases of Cell Cycle cont.
INTERPHASE (3 phases)
1. G1 phase (Growth 1- just after cell is
formed)
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Very active metabolically-- biochemical
pathways: photosynthesis, cell respiration,
biosynthesis
↑ in molecules-- enzymes, hormones,
proteins, mRNA
↑ in number of cellular organelles
↑ in size-- usually doubles in size
Length varies from hours to several days
INTERPHASE (3 phases)
2) S phase (Synthesis- must
occur prior to mitosis)
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DNA double exactly
(replication) all genes copies
DNA polymerase (enzyme) is
very active-- nucleotide
assembly
Histone proteins (for DNA
support) increase
Nucleosomes formed (DNA
packing occurs)
Usually 3-6 hours
2 chromatids attached at
centromere-- end result
INTERPHASE (3 phases)
3) G2 phase (Growth 2- getting ready for
division)
• Twice as much DNA as G1
• Protein synthesis (microtubules/ microfilaments)
form spindles
• Centrioles replicate (in animal cells only)
• 2-5 hours, relatively constant among cells
MITOSIS (P, M, A, T)
• Phases covered later
CYTOKINESIS
• Division of the cytoplasm
• Occurs during telophase of mitosis
2 Major Phases of Mitotic Cell Division
1) MITOSIS
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Process of cell division in eukaryotic cells in
which the nucleus is divided into 2 nuclei,
each with the same number and kinds of
chromosomes
This phase is divided into the:
a. Growth period-- Interphase
b. And 4 stages-- Prophase, Metaphase,
Anaphase, Telophase (P,M,A,T)
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The stages conserve chromosome number
by equally distributing replicated
chromosomes to each of the daughter cells
2 Major Phases of Mitotic Cell Division cont.
2) CYTOKINESIS
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The division of the cytoplasm to form 2
separate daughter cells immediately after
mitosis
MITOSIS (replication and division of the nucleus)
1) INTERPHASE
a. G1 phase
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Growth phase of a cell
Cell grows rapidly and carries out its routine
functions
For most organisms, this phase occupies the
major portion of the cell’s life between cell
divisions
b. S phase
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Time during which DNA is being replicated
At the end of this phase, an individual
chromosome consists of 2 chromatids attached by
a centromere
MITOSIS – INTERPHASE cont.
c. G2 phase
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Time during which preparations are made for
nuclear division
Mitochondria and other organelles replicate
Microtubules reassembled-- will be used to form
the spindle apparatus that moves the
chromosomes
d. M phase
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Phase where mitosis occurs
Mitosis is the replication and division of the
nucleus to form 2 identical nuclei, each with the
same number and kinds of chromosomes
Cell Cycle
Interphase
MITOSIS
2) PROPHASE: 2 Major
Phases
a. Early Prophase
o Replicated chromatids
are present
o Replicated centrioles
(only in animal cells)
migrate to opposite
poles of the cell
o Spindle fibers become
visible
b. Late Prophase
o Nucleolus and nuclear
envelope disintegrate
o Chromatids condense
to form dense coils
Prophase
MITOSIS cont.
3) METAPHASE
o Chromatids are at the
same midline (called the
equatorial plate in
plants)
o Spindle fibers are very
dense
o In animal cells, the aster
is visible around the
centrioles
Metaphase
MITOSIS cont.
4) ANAPHASE
o Centromeres separate and the chromatids
now become individual chromosomes
o Chromosomes migrate to opposite poles of
the cell
Anaphase
MITOSIS cont.
5) TELOPHASE
o Phase of mitotic cell division in which the
cytoplasm divides and 2 identical cells form
o Cytokinesis occurs during this phase
2 Major Differences Between Animal and Plant Cell Division
Animal vs Plant
MITOTIC CELL DIVISION IN PLANT CELLS
MITOTIC CELL DIVISION IN PLANT CELLS cont.
MITOSIS
PRACTICE! Name that Stage!
PRACTICE! Name that Stage!
PRACTICE! Name that Stage!
PRACTICE! Name that Stage!