Download The Cell Cycle and Mitosis

The Cell Cycle
 The cell cycle is the
sequence of events that
occur in a eukaryotic cell
leading up to and
including cell division.
 The two major “parts” of
the cell cycle are:
 Interphase
 Mitosis/Cytokinesis
Interphase
 Before a cell can divide,
it needs to acquire the
necessary nutrients
needed to divide as well
as make other
preparations.
 All these things are done
during a period of the
cell cycle called
Interphase.
Interphase
 Interphase makes up the
majority of the cell cycle
as the cell is usually
spending most of its
time growing and
preparing to divide
rather than dividing
itself.
 That is why Interphase is
further subdivided into
three stages.
Gap 1 (G1) Phase
 This first stage of
Interphase is where the
cell grows and obtains
nutrients needed for the
creation of enzymes
needed in future stages.
Synthesis (S) phase
 This part of Interphase is
where the cell’s DNA is
copied, so that there are
now two copies of each
chromosome.
Gap 2 (G2) Phase
 In this final stage of
Interphase, the cell is
preparing to divide.
 It creates lots of
microtubules, a special
part of the cell’s
cytoskeleton, which
allows the cell to easily
move contents around
inside its cytoplasm.
Mitosis
 Once Interphase is
complete, the cell is ready
to divide.
 That division consists of
two linked, but
independent events known
as mitosis and cytokinesis.
 Mitosis is the division of
the nucleus into two equal
parts whereas cytokinesis
is the separation of the
cell’s organelles into the
formation of two new cells.
Mitosis
 Mitosis deals solely with
the contents of the
nucleus.
 It consists of four
“phases” which separate
the chromosomes
equally, creating two,
genetically identical,
daughter nuclei.
Prophase
 The first phase of mitosis.
 The nuclear membrane
dissolves.
 The chromosomes become
more visible and are
attached to their copy by a
special protein known as a
centromere.
 Special organelles known
as centrioles move towards
the “poles” of the cell.
Metaphase
 Chromosome pairs,
known as sister
chromatids, line up at
the “equator” of the cell.
 Spindle fibres emerge
from the centrioles and
attach to the centromere
of each chromosome
pair.
Anaphase
 The spindle fibres
contract, breaking the
centromere, and pull
apart the sister
chromatids.
 One copy of the
chromosome pair goes to
one pole, while the other
copy goes to the other
pole.
Telophase
 The last stage of mitosis,
where the nuclear
membrane starts to reform
around the chromosomes
that have been pulled to
each pole and two new
nuclei have formed.
 The cell membrane starts
to pinch inward at the
equator signaling the end
of mitosis and the
beginning of cytokinesis.
Cytokinesis
 Cytokinesis means
“movement of cytoplasm”.
 Once the cell has two new
nuclei formed, it starts
moving organelles to each
pole and the cell
membrane that has
pinched inward at the
middle will finally split the
cell into two new, identical
daughter cells.
Resting (G0) Phase
 After mitosis/cytokinesis,
the cell goes through a
brief resting stage before
starting Interphase once
again.
 The length of the resting
stage differs depending
on the cell type.
Apoptosis
 Occasionally an error may
occur during Interphase or
Mitosis which renders the
cell useless.
 These cells usually go
through apoptosis, or
programmed cell death
(PCD) in which the cell is
surrounded and destroyed
before it can cause damage
to surrounding cells.
Cancer
 Unfortunately,
sometimes there are
problems with the cell
cycle itself causing cells
to divide more rapidly
than they are supposed
to, which is called
cancer.
Cancer
 The rapidly dividing cells
create a mass called a tumor.
 Tumors can be benign or
malignant.
 The difference is that
malignant tumors can invade
adjacent tissues and use the
circulatory or lymphatic
systems to travel to and create
cancer in other places in the
body.
 Benign tumors do neither of
these and only produce a
localized swelling or lump.
Cancer
 Scientists are currently
researching how cancer
cells are created in the
body in the hopes of
shutting down this
process and thus
preventing many of the
cancers present today.