Chapter 18: The Cell Cycle Flashcards
list 3 reasons why cell division is needed
- reproduction
- growth
- regeneration
unicellular organisms primarily use cell division for
reproduction
in multicellular organism cell division is important in
- growth
- repair of tissues
what 4 events must occur for cell division?
- reproductive signal
- replication
- segragation
- cytokinesis
the reproductive signal is necessary to
initiate cell division
replication refers to the
duplication of chromosomes
segregation is the distribution of
replicated chromosomes to the 2 daughter cells
cytokinesis is the
separation of the 2 new cells
in prokaryotes binary fission results in
2 new cells
what are 2 external factors that initiate cell division?
- nutrient concentration
- environmental conditions
in bacteria what speeds up the division cycle?
abundant food supplies
in eukaryotic somatic cells each contain a
homologous pair of chromosomes
- each parent contributes 1 homolog
for mammals all somatic cells possess
diploid (2n DNA)
germ cells lead to the production of
gametes
gametes ONLY contain
1 set of chromosomes (haploid= 1n)
fertilization is when
2 haploid gametes fuse
fertilization leads to the formation of a
diploid zygote (2n)
what are the 2 types of cell division in eukaryotes?
- mitosis
- meiosis
in what cells does mitosis occur?
in somatic cells
in what cells does meiosis occur?
in germ cells
mitosis results in
2 identical sister cells
meiosis produces
4 haploid daughter cells different from each other and the parent
what are the 4 stages, in order, of the cell cycle?
- G1
- S
- G2
- M
what are examples of some things that are synthesized in the G2 phase?
- signaling molecules
- regulatory proteins
- histone proteins
- tubulin
during what stage of the cell cycle does reformation of the nuclear envelope occur?
cytokinesis
reformation of the nuclear envelope allows for
uncoiling of the chromosomes
what are the stages of mitosis?
- interphase
- prophase
- prometaphase
- metaphase
- anaphase
- telophase -> cytokinesis
in early embryonic development cell division occurs but there is little
growth
what stage of the cell cycle is skipped during early embryonic development?
G1 & G2
without G1 or G2 cells will continue to
decrease in size
for budding yeast what is the name of the regulatory check point?
START
What factors affect the START check point in yeast?
- nutrient availability
- mating factors
- cell size
to maintain a constant size yeast cells must reach a minimum size to
pass START
what is the resting state for mammalian cells?
G0
what are the 4 cell cycle checkpoints
- DNA damage (G1)
- DNA damage (S)
- DNA damage (G2)
- spindle assembly (M)
the G1 checkpoint checks for
- cell size
- nutrients
- GFs
- DNA damage
checkpoint for DNA damage in G1 is mediated by
p53
the S phase checkpoint includes coupling of the
S to G2 and M phase
what is the licensing factor of the S phase checkpoint?
MCM helicase
MCM helicase can only bind in
G1
the S phase checkpoint prevents DNA from being replicated more than once..how is this done?
by preventing the cells in G2 from reentering S phase
when does the MCM helicase bind?
in the junction between G1 & S phase
the G2 checkpoint of the cell cycle checks for
- cell size
- DNA replication
- DNA damage
the checkpoint for DNA damage in G2 is mediated by
Chk1 & Chk2
the checkpoint during the M phase checks for
- chromosome attachment to spindle
- chromosome alignment
what checkpoint occurs prior to anaphase?
the spindle assembly checkpoint
when do the 2 resting states occur during the cell cycle?
- G1
- M
progression of the cell cycle is regulated through
- kinases
- phosphatases
kinases…
phosphorylates proteins
phosphatases
dephosphorylates proteins
what are the 3 key components of cell cycle regulation?
- maturation promoting factor (MPF)
- Cdc
- Cyclins
MPFs were first studied in
frog oocytes
in MPFs the transition from G2 to M is mediated by
Cdk1 & cyclin B
CDK1 and cyclin B are together known as the
maturation promoting factor (MPF)
Cdc was first studied in
yeast
cdc stands for
cell division mutants
the temperature sensitive mutants were found to undergo ___________ ____________ during specific points in the cell cycle.
growth arrest
most Cdcs have been identified as
kinases called cyclin dependent kinases (Cdk)
cyclins were discovered in what studies?
sea urchin
during the sea urchin studies a series of proteins were identified to display a periodic pattern of
accumulation & degradation
complexes of cyclin & Cdk trigger proteins at
checkpoints
activation of Cdk-cyclin complexes requires
phosphorylation: kinases
dephosphorylation: phosphatases
the Cdk/cyclin complex phosphorylates other ___________ which induces…
- proteins
- progression through the cycle
what cdk/cyclin complex corresponds to the G1 phase?
Cdk4,6/CycD
what cdk/cyclin complex corresponds to the G1-S phase?
Cdk2/CycE
what cdk/cyclin complex corresponds to the S phase?
Cdk2/CycA
what cdk/cyclin complex corresponds to the G2 phase?
Cdk1/CycB
how are cyclins degraded?
by becoming ubiquitinated
which cdk/cyclin complex is responsible for pushing cells past the G1 restriction point?
cdk4,6/cyclinD
cdk4,6 is constitutively…
expressed
cyclin D is synthesized in the presence of
GFs
Rb physically inhibits
E2F
E2F is the transcription factor that transcribes the next cyclin known as
cyclin E
synthesis of cyclin D activates ___________ which phosphorylates _____. ____________ then promotes the transcription of _______________ ___.
- Cdk4,6
- Rb
- E2F
- cyclin E
MCM can only bind in what phase of the cell cycle?
S phase
what couples S phase to G2 phase?
Cdk2/cyclin E and MCM
activated cdk2/cyclin E phosphorylates and activates
MCM
what does MCM do to DNA?
denatures it for replication in the S phase
Cdk 1 activation is through the phosphorylation of
threonine-161
Cdk1 inhibition is through the phosphorylation of
Tyr15
what is the MPF composed of
Cdk1/CyclinB
MPF is inactivated by
cyclin B degradation
what controls the timing of cell cycle events by inhibitory phosphorylation of Cdks?
wee1 kinases
what removes inhibitory phosphates from Cdks?
Cdc25 phosphatase
removal of inhibitory phosphates controls the
entry & progression of the cell cycle
what are 4 functions of mitotic protein kinases?
- chromatin condensation
- nuclear envelope breakdown
- fragmentation of Golgi
- spindle formation
what are the steps in the progression to anaphase?
MPF -> APC activation -> MPF Ubiquitination -> MPF degradation
ubiquitination of securin causes an active ________ that leads to the degradation of ___________.
- separase
- cohesin
what is a target of cyclin D/Cdk 4,6 that is often mutated in a wide array of human tumors?
RB
Rb is the prototype of a tumor suppressor genes b/c its a gene whose
inactivation leads to tumor development
the proteins encoded by tumor suppressor genes act as
brakes slowing down cell cycle progression
GF signaling activates what pathway?
the Ras pathway
Ras activation uses what cdk/cyclin complex?
Cdk4,6/Cyclin D
an active Rb binds E2F transcription factor preventing
- transcription of genes for DNA replication
- passage through G1 into S phase
when can Rb not bind to E2F?
when phosphorylated
phosphorylated Rb cannot bind to E2F leading to
- activation of gene transcription triggering onset of S phase
when DNA damage is detected the cells arrest in _____ which activates _____ & ______these phosphorylate _____.
- G1
- ATM & Chk2
- p53
activated p53 causes transcription of ______. This inhibits the activity of _____________. what does this inhibit?
- p21
- Cdk2/cyclin E
inhibits:
- G1 to S transition
- replication
in early G1 p27 inhibits
Cdk2/Cyclin E
GF signaling causes the
degradation of p27 through phosphorylation
in late G1 ___________ gets involved leading to…
- MCM
- DNA replication
Chk1 and Chk2 are
inhibitors of cell cycle progression
