There
is
also
a
G2
checkpoint
that
controls
entry
into
the
mitotic
phase
and
a
metaphase
checkpoint
that
stops
progression
to
____________________
.
However
,
most
cells
usually
proceed
through
the
cell
cycle
once
beyond
the
G1
checkpoint
or
____________________
point
.
The
mitotic
phase
refers
to
the
division
of
the
parent
cell
into
two
____________________
daughter
cells
.
Two
distinct
but
overlapping
processes
that
happen
in
this
phase
are
:
karyokinesis
(
the
division
of
the
nucleus
)
and
cytokinesis
(
the
division
of
the
cytoplasm
)
.
Mitosis
can
be
broken
down
into
:
prophase
,
metaphase
,
anaphase
,
and
telophase
.
Metaphase
can
be
further
broken
down
into
____________________
and
metaphase
.
Mitosis
is
a
continuous
process
;
the
4
phases
of
mitosis
____________________
into
each
other
.
In
prophase
,
the
chromosomes
appear
(
each
chromosome
consists
of
two
chromatids
that
are
held
together
by
the
centromere
)
.
The
centrioles
also
duplicate
and
move
with
their
centrosomes
to
opposite
ends
of
the
cell
.
In
late
____________________
,
the
division
of
the
chromosomes
into
chromatids
is
clearly
seen
.
It
can
also
be
noted
that
a
cluster
of
microtubules
called
an
aster
extends
from
the
centrioles
and
begins
to
form
the
mitotic
spindle
and
the
nucleoli
disappear
.
In
prometaphase
,
the
____________________
envelope
breaks
down
,
releasing
the
chromosomes
into
the
cytoplasm
.
Additionally
,
kinetochores
form
around
the
centromeres
of
chromosomes
and
____________________
microtubules
attach
to
them
.
It
is
important
to
not
confuse
kinetochore
microtubules
with
____________________
microtubules
,
which
radiate
from
each
aster
.
Polar
microtubules
push
against
each
other
,
moving
centrosomes
apart
.
During
metaphase
,
microtubules
pull
chromosomes
,
lining
them
up
along
the
____________________
of
the
cell
(
equatorial
plane
or
metaphase
plate
)
.
A
cell
can
only
enter
anaphase
once
it
ensures
that
all
the
chromosomes
are
properly
aligned
and
have
kinetochore
microtubules
attached
to
them
.
If
for
instance
,
it
was
found
that
one
chromosome
does
not
have
kinetochore
microtubules
attached
to
it
,
then
the
cell
would
not
____________________
to
the
next
phase
and
would
instead
enter
the
G0
phase
.
During
anaphase
,
cohesin
proteins
are
____________________
to
allow
sister
chromatids
to
separate
from
one
another
.
Kinetochore
microtubules
pull
sister
chromatids
towards
the
opposite
ends
of
the
cell
.
As
kinetochore
microtubules
pull
sister
chromatids
,
another
process
occurs
at
the
same
time
:
polar
microtubules
(
non
-
kinetochore
microtubules
)
elongate
.
This
pushes
the
____________________
and
the
set
of
chromosomes
to
which
they
are
attached
to
opposite
ends
of
the
cells
.
In
telophase
,
the
mitotic
spindle
disassembles
,
but
polar
microtubules
remain
and
further
____________________
.
The
nuclear
envelope
and
nucleoli
____________________
,
and
chromosomes
uncoil
to
form
chromatin
.
During
cytokinesis
(
which
starts
at
____________________
and
continues
through
telophase
)
,
the
parent
cell's
cytoplasm
divides
into
two
daughter
cells
with
one
nucleus
in
each
.
Essentially
,
a
ring
of
actin
microfilaments
called
the
____________________
ring
forms
around
the
equator
of
the
cell
just
beneath
the
plasma
membrane
.
This
ring
shrink
,
pinching
the
plasma
membrane
inward
(
this
is
called
furrowing
and
it
forms
what
is
called
a
____________________
furrow
)
.
Eventually
,
the
ring
____________________
until
there
are
two
separate
cells
bound
by
their
own
plasma
membranes
.
The
time
taken
for
each
of
the
phases
of
mitosis
varies
.
Mitosis
itself
lasts
from
30
minutes
to
3
hours
.
____________________
are
proteins
that
control
the
cell
cycle
at
each
checkpoint
.
Cyclin
____________________
vary
through
the
cell
cycle
.
Cyclins
trigger
the
transition
from
G1
to
S
phase
and
from
G2
to
M
phase
by
activating
enzymes
called
Cyclin
-
dependent
kinases
(
____________________
)
by
binding
to
them
.
These
enzymes
activate
other
proteins
(
such
as
____________________
-
retinoblastoma
protein
)
by
phosphorylating
them
.
pRb
is
a
tumor
suppressor
and
phophorylating
it
prevents
it
from
inhibiting
DNA
replication
.
As
mentioned
earlier
,
cyclins
bind
to
Cdks
forming
cyclin
-
cdk
complexes
that
trigger
or
regulate
each
step
of
the
cell
cycle
.
In
essence
,
cyclin
-
cdk
complexes
control
the
progression
of
a
cell
from
one
checkpoint
to
another
.
In
cancer
,
cyclin
levels
are
often
much
higher
than
normal
and
the
tumor
____________________
protein
p53
is
usually
absent
at
the
G1
phase
allowing
progression
to
the
S
phase
.
The
protein
p53
suppresses
cell
division
and
without
it
the
cancer
cells
will
continue
to
____________________
rapidly
and
cause
tumors
.
Certain
anti
-
cancer
drugs
can
stop
the
cell
cycle
at
specific
checkpoints
.
Vinca
alkaloids
are
drugs
arrest
cancer
cells
in
mitosis
.
Cytarabine
,
methotrexate
,
and
flourouracil
arrest
cells
in
S
-
phase
.
Cisplatin
is
a
drug
that
stops
DNA
replication
.
Two
side
effects
of
these
drugs
are
nausea
and
hair
loss
because
of
their
effect
on
the
digestive
tract
and
hair
follicles
.
There
are
however
medications
that
are
given
to
patients
to
combat
these
side
effects
.
