Unit Three
“Cell Proliferation and Genetics”
“Mitosis”
Prokaryotic Cell Cycle
 Prokaryotic cell division occurs in two
stages, which together comprise a “Simple
Cell Cycle”
– A) DNA Replication
– B) Cell divides in process known as “Binary
Fission”
*** Each new cell contains one chromosome and
is a complete prokaryotic organism
Eukaryotic Cell Cycle
 The eukaryotic cell cycle is much more
complex than that of prokaryotes due to the
following factors:
– 1. cells are larger
– 2. many more organelles
– 3. much more DNA arranged in linear segments
known as “Chromosomes”
– 4. cell division is more complex due to above
factors
Eukaryotic Cell Cycle
Eukaryotic Cell Division
 Division of nonreproductive cells is called
“Mitosis”
 Nonreproductive cells are referred to as
“Somatic Cells”
 Mitosis involves the even division of
chromosomes and organelles between two
cells that are not part of the reproductive
system
 The parent cell undergoing Mitosis has a
Diploid number (2n) of chromosomes
 The two daughter cells that result from Mitosis
have a Diploid number(2n) of chromosomes
Eukaryotic Cell Division
 Division of reproductive cells is called “Meiosis”
 Reproductive cells are referred to as “Germ
Cells”, and upon completion of Meiosis those
cells are called “Gametes”
 Meiosis is often referred to as “Reduction
Division” because the number of chromosomes
is reduced from the Diploid number (2n) to the
Haploid number (n)
 One parent cell with a Diploid number results in
four daughter cells with a Haploid number
Chromosomes
 First observed by German Embryologist
Walther Fleming 1882
 What he saw under his primitive microscope
were thread-like structures of salamander larval
cells appearing to separate lengthwise
 He called the division “Mitosis” based on the
Greek word “Mitos”, meaning thread
 Number of chromosomes vary greatly by
species: Humans (46), House Cat (18), Plants
(100’s)
Chromosomes
 In Somatic Cells, Chromosomes group
together in pairs based on size and genetic
information; they are called “Homologous
Chromosomes” or “Homologues”
 Before cell division, each Homologous
Chromosome replicates resulting in two
identical copies called “Sister Chromatids”
 The “Sister Chromatids” remain joined after
duplication and prior to cell division at the
center or their structures; this area is called the
“Centromere”
Chromatin
 During Interphase, the macromolecular
complex of DNA and Protein is referred to as
“Chromatin”, as stated previously
 Chromatin is 40% DNA and 60% Protein
 The reason there is a large proportion of
protein associated with the DNA structure is
chemical in nature
 The proteins allow the DNA to thicken and coil
in preparation for cell division; if there were no
proteins present, this would not happen
Chromosomes
 Often in discussion, the long strands of DNA
are called “Chromosomes”
 However, DNA strands are actually referred to
as “Chromosomes” only during cell division
(whether it is mitosis or meiosis)
 The above is the case because it is just prior to
cell division that the DNA strands thicken and
coil taking on a unique appearance, that of a
“Chromosome”
 Throughout the majority of the cell cycle
(Interphase), the DNA strands are called
“Chromatin”
Cell Division
 Cell Division takes approximately 1 hour of the
24 hour Cell Cycle
 Cell Division has four distinct phases
 Some scientists further subdivide those phases
into five or more
 The four phases in order are:
–
–
–
–
A) Prophase
B) Metaphase
C) Anaphase
D) Telophase
Prophase
 1. Chromosomes begin to migrate to the
center of the cell
 2. Chromosomes also pair up with their
homologue
 3. The Nuclear membrane degrades
 4. The Centrioles appear, migrate to
opposite ends of the cell, and project their
Spindle Fibers outward toward the
Centromeres of the Chromosomes
Prophase
Metaphase
 1. The Chromosomes are lined up in the
middle of the cell
 2. The Nuclear Membrane has completely
disintegrated
 3. The Centrioles’ Spindle Fibers attach to
the centers of the Chromosomes, the
Centromeres, in preparation to pull the
Chromosomes apart
Metaphase
Anaphase
 1. Spindle Fibers from the Centrioles pull the
Chromosomes apart toward opposite ends
of the cell
 2. Once the Chromosomes separate they
are referred to as “Sister Chromatids”
Anaphase
Telophase
 1. Each set of Sister Chromatids has been pulled to
opposite ends of the parent cell
 2. The Nuclear Membrane begins to reform around
two new nuclei (the locations of the sister
chromatids)
 3. The Sister Chromatids begin to uncoil and loosen,
and now are designated as Chromosomes
 4. The Plasma Membrane of the parent cell begins
to “pinch off” into two new membranes via
“Cytokinesis”
 5. The Centrioles deactivate and “disappear” into the
cytoplasm
Telophase
Miscellaneous Cell Cycle
Information
 Cytokinesis – the division of the cytoplasm at the
end of cellular division
 Cleavage Furrow – the physical action of the parent
cell’s cytoplasm being pinched apart during
Cytokinesis
 Mitosis is sometimes referred to as “Karyokinesis”
 Plant cells use a “Cell Plate” (wall in the center of
the parent cell) to divide the cytoplasm instead of a
“Cleavage Furrow”
 It is important to understand that a cell does not
necessarily divide every 24 hours: it can enter a
“stasis” until environmental conditions are more
favorable
Cancer
 Old/malfunctioning cells do not die and
continue to reproduce improperly functioning
cells
 Bundles of cells that are malformed are
called “Tumors”
 Some of the cells in the tumor can then
migrate to other parts of the body, thereby
enabling the proliferation of more cancerous
cells/tumors in other locations: “Metastases”
Cancer Treatment
 The conventional approach to treating, and
hopefully curing cancer, is Chemotherapy
and Radiation
 Chemotherapy – a chemical that is delivered
to the person usually intravenously; the drug
targets and kills cancer cells
 Radiation – high frequency energy delivered
to a person’s body via a machine in an effort
to target and kill cancer cells
 There are many forms of cancer each with a
unique set of treatment options