The Key Roles of Cell Division
• Essential for
perpetuation of life:
Reproduction of
unicellular forms
• Development,
Growth, & Repair of
multicellular forms
The Mitotic Cycle
• Interphase  90%
– G = Grow, normal fx.
1
– S = Synthesis of DNA
– G2 = Prepares for cell division
• Mitosis
– PMAT
• Cytokinesis –cell pinches
in 2
Interphase
• Nucleus is well
defined in a nuclear
envelope
• DNA is in the form of
loosely packed
chromatin fibers
• Accounts for 90% of
cell cycle
• Chromosomes become
visible
• The nucleoli and nuclear
envelope begin to
disappear
• Spindle forms
Prophase
Metaphase
• Chromosomes line up along the Middle
Anaphase
• chromosomes move
to opposite poles of
the cell.
Telophase
• Nuclear envelope
forms at each pole
• Chromosomes uncoil
• Cleavage furrow
• http://www.cellsalive.c
om/cell_cycle.htm
• http://www.cellsalive.c
om/mitosis.htm
Conjoined Twins
http://www.youtube.com/watch?v=ZzZYKg
grB34&feature=fvsr
http://www.youtube.com/watch?v=XM82Hs
0LEpc
5.4 Cell Cycle
Control
and Mutation
Controls in the Cell
Cycle
• Checkpoints exist in
the cell cycle
• Cell determines if cell is
ready to enter next part
of cell cycle
http://highered.mcgrawhill.com/olc/dl/120082/bio
34a.swf
5.1 What Is Cancer?
• Cancer begins when the proteins that regulate the cell cycle
don’t work, the cell divides uncontrollably
– Mutations can be inherited or induced by exposure to U.V. radiation or
carcinogens that damage DNA and chromosomes
Cancer: Uncontrolled cell growth
• Tumor
– Malignant vs benign
• Metastasis
• Types of cancer
– Carcinoma (epithelials)
• Melanoma (melanocytes)
– Sarcoma
(muscle/connective)
– Osteogenic (bone)
– Leukemia (blood forming
organs) ↑ WBC’s
– Lymphoma (lymphatic)
• Malignant cells trigger
angiogenesis
Mutations to Cell-Cycle
Control Genes
• Proto-oncogenes: Normal genes on many different
chromosomes regulate cell division
• When mutated, they become oncogenes
• Many organisms have proto-oncogenes, so many
organisms can develop cancer
From Benign to Malignant
• Angiogenesis – growth
of blood cells caused
by secretions from
cancer cells
– Increases the blood
supply to cancer
cells: more oxygen
and nutrients
• Cancer cells can divide
more
• Tumors develop,
sometimes filling entire
organs
From Benign to
Malignant
• Contact inhibition in
normal cells prevents
them from dividing all
the time, which would
force the new cells to
pile up on each other
• Anchorage
dependence in normal
cells keeps the cells in
place
Multiple Hit Model
• Many changes, or hits, to
the cancer cell are
required for malignancy
• Mutations can be
inherited and/or can
stem from environmental
exposures
• Knowledge of cancer
risk factors is important
• Earlier detection and
treatment of cancer
greatly increase the odds
of survival
Detection Methods:
Biopsy
• Different cancers are
detected by different
methods, including high
protein production
possibly indicating a
tumor
• Biopsy, the surgical
removal of cells, tissue,
or fluid for analysis is
performed
• Under a microscope,
benign tumors appear
orderly and resemble
other cells in the same
tissue
• Malignant tumors do not
resemble normal tissue
5.6 Meiosis
•
•
•
•
Occurs within gonads (testes:ovaries)
Meiosis produces sex cells – gametes (sperm:egg)
Gametes have half the chromosomes (23) that somatic cells do (46)
Meiosis reduces the number of chromosomes by one-half
Meiosis
contributes
to Genetic
Variation
• There are millions of
possible combinations
of genes that each
parent can produce
because of:
– Random alignment
of homologous pairs
– Crossing over
– Random
Feritlization (70
trillion)
Birth = paused at prophase I
Puberty = finishes meiosis I
Fertilization = finishes meiosis
*somatic cells
*divide once diploid
*forms identical cells
http://highered.
mcgrawhill.com/sites/0
072437316/stu
dent_view0/ch
apter12/animat
ions.html#
*gametes
*divide twicehaploid
*forms different cells
(crossing over)