Chp. 18 - Cell Cycle Flashcards
What would be the most obvious outcome of repeated cells consisting of S phase and M phase only?
The cells produced would get smaller and smaller.
Levels of Cdk activity during the cell cycle, in part because ____.
cyclin levels change during the cycle
____ drives cells through G1.
G1-Cdk
_____ and ____ drives it into S phase.
G1/S-Cdk; S-Cdk
G1/S-Cdk and S-Cdk drives it into ___ phase.
S
___ initiates DNA replication during S phase and helps ensure the genome is copies only once.
S-Cdk
Centrosomes duplicate during __ phase and separate during ___.
S; G2
____ drives the cell into mitosis.
M-Cdk
Cyclins concentrations are regulated by ____ and ____.
transcription and proteolysis
Cyclins are regulated…. ______ via gradual increase in cyclins. ____ via quick decrease in cyclins.
transcription; proteolysis
What is APC?
Anaphase Promoting Complex
Cyclin concentration is regulated by ___ and ____.
transcription; proteolysis
The activity of cyclin-cdk complexes depends on ___ and ___.
phosphorylation; dephosphorylation
When the M cyclin and the mitotic Cdk make a complex, they have two phosphates that were put there by ____.
inhibitory kinase (Wee1)
The cyclin Cdk complex contains inhibitory phosphates This modification keeps M-Cdk in a/an _____.
inactive state
For the M-Cdk to become active, it must dephosphorylated by ____.
CDC 25
CDC 25 actually involved in activation of ____.
M-Cdk
Cdk activity can be blocked by ______ proteins.
Cdk Inhibitor
What inhibitor makes the active cyclin-Cdk complex inactive?
p27
What is the main molecular difference between cells in a G0 state and cells that have simply paused in G1?
* Cells in the G0 state do not divide * In G0, the cell-cycle control system is partly dismantled, so that some of the Cdks and cyclins are not present. Cell paused in G1, by contrast, still contain all the components of the cell-cycle control system. Whereas the latter cells can rapidly progress through the cycle when conditions are right, G0, cells need to synthesize the missing cell-cycle control proteins so as to re-enter the cycle, which usually takes 8 hours or more.
___ are extracellular signal that stimulate cell division by the production of the cyclins. If deprived of this signal, the cell cycle arrests in __.
Mitogens; G1
The ___ protein blocks cells from entering the cell cycle by inhibiting cyclin transcription.
Rb
Mitogens promote cell division by activating ___ and ___ which inactivate the __ proteins.
G1-Cdk; G1/Cdks; Rb
DNA damage can arrest the cell cycle in __.
G1
How does S-Cdk help guarantee that replication occurs only once during each cell cycle?
It phosphorylates the Cdc6 protein making it for destruction.
Sister chromatids are held together by ___ complexes until anaphase.
cohesin ring
Activation of __ by ___ leads to entry into M phase.
M-Cdk; Cdc25
Before a cell can enter M phase, what two structures must be duplicated?
1- DNA must be fully replicated; 2- The centrosome must be duplicated
Centrosome duplication begins at the start of the __ phase and is complete by the end of ___.
S; G2
Which of the following correctly matches the phase of the eukaryotic cell cycle with an event that takes place in that phase?
M phase—cytokinesis
Which is NOT a transition point where the cell cycle control system regulates progression through the cell cycle?
S/G2 transition
The expression levels of different ___________ fluctuate throughout the cell cycle.
cyclins
The slow rise of S cyclin levels throughout G1 phase is due to ___________, and the abrupt decrease is caused by ___________.
transcription; proteolysis
In response to DNA damage, the ___________ protein is phosphorylated and activates the transcription of a Cdk inhibitor to halt cell cycle progression.
p53
How does S-Cdk prevent re-replication?
phosphorylation of ORC and Cdc6
M-Cdk is suddenly activated at the end of G2 by ___.
dephosphorylation by Cdc25
What is the function of cohesins?
hold two sister chromatids together during replication.
The figure below shows some steps involved in the initiation of DNA replication. What is the identity of the complex labeled “B”?
ORC
What accounts for the difference in the curve shapes depicting the concentration of M-cyclin versus M-Cdk activity during the cell cycle?
The M-Cdk complex is not activated until M-cyclin is bound and M-Cdk is dephosphorylated.
Consider an animal cell that has 8 chromosomes (four pairs of homologous chromosomes) in the G1 phase. How many of each of the following structures will the cell have at mitotic prophase?
A. sister chromatids
B. centromeres
C. kinetochores
D. centrosomes
E. Centrioles
A. sister chromatids: 16
B. centromeres: 16
C. kinetochores: 16
D. centrosomes: 2
E. Centrioles: 4
If chromosome is attached to two microtubules from opposite poles and one of the microtubules is experimentally severed, what occurs?
The chromosomes migrate quickly to the pole to which it is still attached.
In the cells of some organisms, mitosis occurs without cytokinesis. This will result in…
cells with more than one nucleus
Place the numbers 1-8 next to the letter headings to indicate the normal order of events.
A. alignment of the chromosomes at the spindle equator;
B. attachment of spindle microtubules to chromosomes;
C. breakdown of the nuclear envelope;
D. pinching of cell in two;
E. separation of two centrosomes and initiation of mitotic spindle assembly;
F. re-formation of the nuclear envelope;
G. condensation of the chromosomes;
H. separation of sister chromatids
A. 5, metaphase
B. 4, prometaphase
C. 3, prometaphase
D. 8, cytokinesis
E. 2, prophase
F. 7, telophase
G. 1, prophase
H. 6, anaphase
The number of cells in adult tissue or animal depends on cell proliferation. What else does it depend on?
Programmed cell death also influences cell numbers. Most animal cells require survival signals from other cells to avoid programmed cell death so that the levels of such signals can help determine how many cells live and how many die.
Bax and Bak promote apoptosis by releasing ____ from the mitochondria.
cytochrome c
What is the cause of the massive amount of programmed cell death of nerve cells (neurons) that occurs in the developing vertebrate nervous system, and what purpose does it serve?
Immature neurons are produced in excess of the number that will eventually be required. They compete for the limited amount of survival factors secreted by the target cells they contact. THOSE CELLS THAT FAIL TO GET ENOUGH SURVIVAL FACTOR UNDERGO PROGRAMMED CELL DEATH. Up to half or more of the original nerve cells die in this way. This competing mechanism helps match the number of developing nerve cells to the number of target cells they contact.
Cohesin is cleaved by the enzyme ___________, which is held in an inactive state by ___________ until it is degraded by the APC/C complex.
separase; securin
What drives the reassembly of the nuclear envelope?
dephosphorylation of lamins
The contractile ring is composed of
actin and myosin.
In response to an apoptotic stimulus, initiator caspases
cleave and activate executioner caspases.
Which of the following cells died by apoptosis?
B
Consider an animal cell that has eight chromosomes (four pairs of homologous chromosomes) in G1 phase. This cell has _________sister chromatids and
_________ centrioles.
16; 4
If a chromosome is attached to two microtubules from opposite poles and one of the microtubules is experimentally severed, what occurs?
The chromosome migrates quickly to the pole to which it is still attached.
What is the function of condensins?
to coil sister chromatids into a compact form
In which phase of mitosis does the nuclear envelope break down?
prometaphase
How are spindle microtubules attached to chromosomes?
The minus ends of the microtubules bind directly to a protein complex on DNA.
The plus ends of the microtubules bind directly to DNA.
The microtubules bind to cohesion complexes on the DNA.
The microtubules bind to the kinetochore complexes through a connecting protein.***
The four phases of the cell cycle, in order, are G1, __, ______2, and ______. A cell contains the most DNA after _________ phase of the cell cycle. A cell is smallest in size after _____ phase of the cell cycle. Growth occurs in ________, _______, and ______phases of the cell cycle. A cell does not enter mitosis until it has completed _________ synthesis.
G1 –> S –> G2 –> M;
S phase;
M phase;
G1, S, and G2;
DNA
Different Cyclin-Cdk complexes Trigger Different Steps in the Cell Cycle. The cyclin that acts in G2 to trigger entry into M phase is called ___________, and the active complex it forms with its Cdk is called _________________, Other cyclins, called _______ and _____________, bind to a distinct Cdk protein late in G1 to form S-Cdk and G1/S-Cdk; these cyclin –Cdk complexes help launch S phase. Another group of cyclins, called _______________, act earlier in G1 and bind to other Cdk proteins to form _________, which help drive the cell through G1.
Different Cyclin-Cdk complexes Trigger Different Steps in the Cell Cycle. The cyclin that acts in G2 to trigger entry into M phase is called M cyclin and the active complex it forms with its Cdk is called M-Cdk, Other cyclins, called S cyclins and G1/S, bind to a distinct Cdk protein late in G1 to form S-Cdk and G1/S-Cdk; these cyclins –Cdk complexes help launch S phase. Another group of cyclins, called G1 cyclin, act earlier in G1 and bind to other Cdk proteins to form G cdk, which helps drive the cell through G1.
The interval between the completion of mitosis and the beginning of DNA synthesis is called ________________, and the interval between the end of DNA synthesis and the beginning mitosis is called ________________.
G1; G2
The cell-cycle control system depends on ____________-dependent protein kinases (Cdks), which are cyclically activated by the binding of ___-__________ proteins and by phosphorylation and _____________; when activated, Cdks phosphorylate key proteins in the cell.
cyclin; cyclin; dephosphorylation
