Cell Cycle Flashcards
what are the three main things cells have to do?
grow, segregate, and divide into two
what is the longest phase of the cell cycle?
interphase
what starts during anaphase
cytokinesis
depending on the type of cell determines what
how long the process is going to take
how many copies of DNA are in G1
one copy
how many copies of DNA are in S phase
1.1-1.9
what is happening in S phase
DNA replication
how many copies of DNA are in G2 phase
two copies
what is happening in G1 phase
it is getting ready for replication
how many times do cells replicate in S phase
once and only once
what is happening in G2 phase
getting ready for mitosis and makes a lot of microtubules to separate sister chromatids
what does START represent
the transition from G1 to S
START marks the
commitment to enter S phase
is the cell cycle a one or two way street
one way street
Flow cytometry determines what
the amount of DNA inside the cell and run it through an automated fluorescent microscope that forces cells to line up in a single file and pass through a laser which takes pics
wherever the arrest or stop is it will continue until it gets to…
that point and thats when it will arrest
examples of cells that are non-dividing
spinal cord, neurons, brain cells, smooth muscle cells of vascular system
what phase are cells non-dividing
G0
what are two major chromosomal events that occur in S phase and M phase
segregation and separation
what question is asked going from g1 to s phase
is the environment favorable?
what questions are asked going from g2 to mitosis
is all dna replicated?
is environment favorable?
what questions are asked in mitosis
are all chromosomes attached to the spindle?
what are two options for cell cycle checkpoints
- temporary cell cycle arrest
- permanent cell cycle arrest
how do the cell cycle checkpoints work?
cell cycle checkpoint work through CDKs
what are CDKs
cyclin-dependent kinases
what do CDKs do
phosphorylate proteins that drive the cell cycle
CDKs must be activated by specific
cyclins
CDK levels are
constant
are CDKs activity constant
no just levels
what determines when the CDKs activate
the concentration of cyclins
cyclin binding moves what
an inhibitory protein loop (T-loop) out of the Cdk active site
what enzyme completes Cdk activation
CAK
CAK stands for
Cdk- activating kinase
what turns CDKs off
WEE1
WEE1 kinase is the only
phosphate that turns something off
what activated CDKs again
Cdc25 phosphatase
Cdc25 phosphatase does what
removes WEE1
what grabs on and prevents the CDKs from doing anything
p27
CDK Inhibitor proteins do what
inactivate cyclin-cdk complexes
what is a tumor supressor
p53
tumor suppressor genes do what
stop cell cycle from progressing
oncogenes act as
gas pedals that drive the cell cycle
DNA damage stimulates
p53
p53 activates the
transcription of CKI protein p21 that stops the cell cycle
what is loaded in G1 but not activated until S phase
pre-replicative complex preRC
what is always bound to the replication origin
ORC
what associated in G1
Cdc6
Cdc6 and ORC together along with Cdt1 do what
load the DNA replication helicase in an inactive form
S-Cdk phosphorylates helicase which is an
activator/ initiator protein
DDK phosphorylates
DNA helicase
phosphorylated DNA helicase initiates
DNA replication
what phosphorylated ORC, Cdc6, and Cdt1 to deactivate them
S-Cdk
when are ORC, Cdc6, and Cdt1 dephosphorylated
at the end of mitosis
why do we had to add cohesion proteins
so when dna replicated we know which strands of DNA go together
during replication cohesion protein deposited
along the length of the chromosome
cohesion rings encircle
both sister chromatids
what triggers condensation of replicated chromosomes and induces the assembly of the mitotic spindle, breaks down the nuclear envelope and rearranges the actin cytoskeleton
M-Cdk
what drives mitosis
M-Cdk
M-Cdk levels build up during
G2 phase
M-Cdk levels build up but is kept inactive by
Wee1
when cells enter M phase what is activated
Cdc25
Wee1 is suppressed and M-Cdk becomes
activated
by inhibiting Wee1 it does what
increases M-Cdk
what is M-Cdk tasked with
condensing our DNA into our sister chromatids
condensin is a
5-subunit protein that coils up DNA
condensin’s activity is stimulated when it is
phosphorylated by M-Cdk
the cytoskeleton allows for
separation of duplicated chromosomes and the division of the cell
M-Cdk initiates
mitotic spindle assembly
microtubules originate from
centrosomes
microtubules pull
chromatids apart
the centrosomes or MTOCS are duplicated early in
S phase
the centrosomes duplicated in S phase form the
spindle poles
astral microtubules are found on
the backside and position the spindle pole at opposite ends of the cell
kinetochore microtubules interact with
sister chromatids
kinetochores orient
back to back
kinetochores reduce the chance that
both sister chromatids will become attached to one spindle pole
the arrangement of the kinetochore is called
bi-orientation
how many microtubules for each spindle pole attached to your sisters
1
what is responsible for anchoring the microtubule at the kinetochore
Ndc80
why is the formation of Ndc80 important
it forms a ring around the side of the microtubule and allows addition and loss at plus end
increased tension increases
microtubule binding affinity
the correct spindle attachment arrangement increases
tension at the kinetochore
astral microtubules position spindles poles
correctly
interpolar microtubules
interdigitate to provide stability and allow movement of the spindle poles
many motor proteins function in concert to align the spindle poles and the chromosomes on the
metaphase plate
APC/C is an
ubiquitin ligase
APC/C does what
gets rid of proteins we don’t need and degrades M cyclins and S cyclins
what is activated by Cdc20 binding
APC/C
activated APC/C causes
sister chromatid separation by degrading securin
separase
a protease which cleaves cohesin
no tension means
no anaphase
chromosomes that is not attached to a spindle is going to
inhibit APC/C
relaxed kinetochore means
not bi-oriented
not bi-oriented means it
changes shape of kinetochore
a relaxed kinetochore alters shape of
Mad2 which activates it
Mad2 binds and inhibits
APC/C
what helps Mad2
BubR1
when we have tension what cant bind
Mad2 and BubR1
nondisjunction means
you do not have correct sister separation
more than 90 percent of tumors are
aneuploidy
aneuploidy means
abnormal chromosome number
if spindle assembly checkpoint does not operate properly during meiosis than gametes will be
aneuploid
down syndrome is from
nondisjunction during maternal meiosis I
klinefelter syndrome
two or more X chromosomes in males
unicellular organisms can afford to be
selfish
if damage is not repaired,
the cell will recommence the cell cycle
permanently arrested cells of multicellular organisms will undergo
apoptosis or programmed cell death
