When
a
cell
reaches
a
certain
size
it
either
stops
growing
or
divides
.
The
stages
through
which
a
cell
passes
from
one
cell
____________________
to
the
next
is
known
as
the
cell
cycle
.
The
time
taken
to
pass
from
one
cell
division
to
another
varies
across
cells
,
however
on
average
it
is
8
-
20
hours
in
____________________
growing
tissues
.
The
cell
cycle
can
be
broken
down
into
two
main
phases
:
interphase
and
mitotic
phase
.
During
interphase
,
the
cell
is
actively
growing
and
metabolizing
(
making
proteins
,
hormones
,
etc
)
.
It
is
also
preparing
for
cell
division
.
When
the
cell
is
not
dividing
,
the
DNA
is
in
the
form
of
chromatin
.
During
prophase
(
the
first
stage
of
mitosis
)
,
chromatin
condenses
into
chromosomes
.
The
advantage
of
condensed
chromatin
is
that
it
is
easier
to
move
it
across
the
cell
.
A
centromere
is
the
region
in
an
x
-
shaped
chromosome
where
the
two
sister
chromatids
join
together
.
A
centromere
consists
of
heterochromatin
(
inactive
DNA
)
.
During
cell
division
,
____________________
attach
to
this
region
to
pull
sister
chromatids
apart
.
Cohesins
are
proteins
that
hold
sister
chromatids
together
in
a
chromosome
.
____________________
are
mainly
concentrated
in
the
centromere
.
When
sister
chromatids
are
pulled
apart
,
these
cohesin
proteins
disassemble
.
During
prometaphase
,
kinetochores
form
on
each
side
of
the
centromere
,
so
there
is
one
kinetochore
per
sister
chromatid
.
____________________
serve
as
points
of
attachment
for
microtubules
to
pull
apart
the
sister
chromatids
during
cell
division
.
____________________
are
repetitive
nucleotide
sequences
that
cap
the
ends
of
sister
chromatids
.
Telomeres
protect
the
ends
of
chromosomes
from
____________________
or
fusing
with
other
chromosomes
.
They
also
maintain
the
structural
____________________
of
the
DNA
,
ensure
complete
DNA
replication
with
telomerase
,
and
position
chromosomes
in
the
nucleus
.
Every
time
a
cell
divides
,
____________________
become
shorter
and
when
the
telomeres
get
too
short
or
are
completely
lost
,
the
cell
can
no
longer
divide
.
Karyotyping
is
the
process
of
pairing
and
arranging
chromosomes
from
largest
to
smallest
to
observe
and
determine
any
abnormalities
.
A
____________________
is
an
individual's
complete
set
of
chromosomes
.
Mitosis
only
occupies
a
brief
period
of
the
cell
cycle
,
so
most
of
the
time
cells
are
in
____________________
.
In
G1
phase
,
the
cell
is
metabolically
active
and
continuously
growing
.
The
cell
is
also
preparing
for
duplicating
DNA
(
high
levels
of
RNA
____________________
and
protein
synthesis
can
be
seen
)
.
Many
of
the
proteins
synthesized
will
be
used
for
DNA
____________________
and
chromosome
replication
during
S
phase
.
It
can
also
be
noted
that
organelles
such
as
the
mitochondria
increase
in
number
.
Another
thing
to
note
is
that
cytokinesis
is
fully
completed
in
G1
.
So
,
in
G1
the
____________________
cell's
cytoplasm
divides
into
two
completely
separate
daughter
cells
.
In
S
phase
DNA
synthesis
and
replication
occurs
,
RNA
transcription
and
protein
synthesis
continues
to
happen
,
and
the
____________________
gets
duplicated
.
By
the
onset
of
G2
phase
,
DNA
should
have
been
already
replicated
.
In
this
phase
the
cell
continues
to
grow
and
is
still
metabolically
active
(
transcribes
RNA
and
synthesizes
proteins
in
preparation
for
mitosis
)
.
The
____________________
of
these
cell
cycle
phases
and
the
frequency
of
mitosis
varies
considerably
in
different
kinds
of
cells
and
tissues
.
A
typical
cell
cycle
would
last
for
24
hours
.
____________________
lasts
for
23
hours
,
while
mitosis
and
cytokinesis
last
for
1
hour
only
.
However
,
there
are
some
types
of
cells
that
can
divide
much
more
rapidly
.
For
example
:
____________________
yeasts
divide
every
90
minutes
and
bacteria
divide
every
____________________
minutes
.
That
is
why
on
hospital
wards
,
infection
spreads
so
quickly
and
precautionary
measures
have
been
put
to
prevent
the
spread
of
infection
.
For
example
you
are
not
allowed
to
wear
long
sleeves
when
examining
the
patient
.
A
cell
can
leave
the
cell
cycle
and
enter
something
called
the
G0
phase
;
otherwise
known
as
____________________
phase
.
In
this
phase
,
the
cell
temporarily
stops
dividing
,
however
it
is
still
metabolically
active
.
The
cell
needs
a
signal
(
some
sort
of
growth
factor
)
to
return
back
to
the
cell
cycle
.
An
example
of
a
cell
that
enters
the
G0
phase
is
the
____________________
cell
.
A
liver
cell
divides
only
once
a
year
.
There
are
other
cells
which
leave
the
cell
cycle
and
permanently
stop
dividing
.
This
can
be
because
of
damaged
DNA
(
____________________
)
or
because
of
age
.
These
types
of
cells
undergo
what
we
call
programmed
cell
death
(
____________________
)
.
Cells
enter
the
G0
phase
from
a
checkpoint
in
the
G1
phase
.
If
damaged
DNA
was
detected
in
the
cell
at
this
checkpoint
,
then
the
cell
will
move
to
the
G0
phase
.
In
total
,
the
cell
cycle
has
____________________
checkpoints
to
ensure
that
complete
genomes
are
transmitted
to
daughter
cells
.
Some
cells
such
as
cardiac
muscle
cells
and
neurons
enter
the
G0
-
like
phase
when
they
reach
maturity
and
they
never
leave
it
.
The
G1
checkpoint
is
regulated
by
a
protein
called
____________________
,
which
delays
DNA
synthesis
that
happens
in
the
S
phase
until
DNA
damage
is
repaired
.
There
is
also
a
G2
checkpoint
that
controls
entry
to
the
mitoti
c
