chapter 18 Flashcards
Cells reproduce by _ a process called the _.
duplicating their contents and dividing in two in
_
cell cycle
The cell grows continuously during _, which consists of _
interphase
_
three phases: G1, S, and G2.
DNA replication is confined to _
S phase.
During M phase, the _ divides in a process called mitosis; then
the _ divides, in a process
called cytokinesis.
nucleus
cytoplasm
During M phase, the nucleus divides in a process called _; then
the cytoplasm divides, in a process
called _.
mitosis
cytokinesis
M phase, for example, is typically much _and G1 much _ .
shorter
longer
The cell-cycle control system ensures that key processes in the cycle _
occur in the proper sequence.
The control system can transiently halt the cycle at specific transition points—in _— if _.
G1, G2, and M phase
_
extracellular or intracellular conditions are unfavorable
checks before entering in MITOSIS
Is all DNA replicated? Is all DNA damage repaired?
checks before PULL DUPLICATED CHROMOSOMES APART
Are all chromosomes properly attached to the mitotic spindle?
checks before ENTER S PHASE
Is environment favorable?
Distinct Cdks associate with different _ to trigger the different events of the cell cycle.
cyclins
Distinct _ associate with different cyclins to trigger the different events of the cell cycle.
Cdks
cyclins that are specifically active during the G1 phase of the cell cycle:
cyclin D
cyclins that help G1 –> S transition:
cyclin E
cyclins that are specifically active during the S phase of the cell cycle:
cyclin A
cyclins that are specifically active during the M phase of the cell cycle:
cyclin B
The activity of some Cdks is regulated by _
cyclin degradation.
_ of S or M cyclin by _ marks the protein for destruction in proteasomes. The loss of cyclin renders _
Ubiquitylation
_
APC/C
_
its Cdk partner inactive.
For M-Cdk to be active, _.
inhibitory phosphates must be removed
As soon as the M cyclin–Cdk complex is formed, it is _ by an _ called _. This modification keeps M-Cdk in an _ state until these phosphates are removed by an _ called _.
!!!!mechanism specific to M-Cdks!!!!!
phosphorylated at two adjacent sites
_
inhibitory protein kinase
_
Wee1
_
inactive
_
activating protein phosphatase
_
Cdc25
The activity of a Cdk can be blocked by the _
binding of a Cdk inhibitor. eg: inhibitor protein (called p27) binds to an activated cyclin–Cdk complex = prevents the Cdk from phosphorylating target proteins
control mechanism when
DNA replication not complete
DNA damage
INHIBITION OF ACTIVATING PHOSPHATASE (Cdc25) BLOCKS ENTRY TO MITOSIS
control mechanism when chromosomes not properly attached to spindle
INHIBITION OF APC/C ACTIVATION DELAYS EXIT FROM MITOSIS
control mechanism when
environment not favorable
Cdk INHIBITORS BLOCK ENTRY TO S PHASE
mitogens :
stimulate cell proliferation
mitogens inhibit
the Rb protein.
dephosphorylated Rb protein (active), what do they do?
holds specific transcription regulators in an inactive state.
Mitogens binding to _ activate _
that lead to the _. These complexes _, and thereby inactivate, the _ protein, releasing the transcription regulators needed to activate the transcription of genes required for entry into S phase.
cell-surface receptors
_
intracellular signaling pathways
_
formation and activation of G1-Cdk and G1/S-Cdk complexes
_
phosphorylate
_
Rb
DNA damage can arrest the cell cycle in _.
G1
When DNA is damaged, specific protein kinases respond by both activating the _ and halting _. _ protein thus accumulates and stimulates the _. The p21 protein binds to G1/S-Cdk and S-Cdk and inactivates them, so that the cell cycle arrests in G1.
p53 protein
_
its otherwise rapid degradation
_
Activated p53
_
transcription of the gene that encodes the Cdk inhibitor protein p21 (same shape and system as p27)
_
explain the initiation of DNA replication (fig 16)
During G1, Cdc6 on ORC (origin recognition complex sitting on origin)
_
HELICASE BINDS, Cdc6 DISSOCIATES from ORC
_
At the start of S, S-Cdk triggers the firing of this loaded replication origin
_
S-Cdk also blocks re-replication by phosphorylating Cdc6 and the ORC = both inactive = prevents reassembly of the prereplicative complex until the Cdks are turned off in the next G1.
Activated M-Cdk indirectly activates _, creating a _
more M-Cdk
positive feedback loop.
APC/C triggers _ by _
the separation of sister chromatids
_
by promoting the destruction of cohesins.
APC/C catalyzes the _ and _ of an _ protein called _, which _ the activation of a proteolytic enzyme called _. When freed from _, _ cleaves the _, allowing the _.
ubiquitylation
_
destruction
_
inhibitory
_
securin
_
blocks
_
separase
_
securin
_
separase
_
cohesin complexes
_
mitotic spindle to pull the sister chromatids apart
(A) In anaphase A, _ The force driving this movement is generated mainly at the _.
the sister chromatids are pulled toward opposite poles as the kinetochore microtubules depolymerize.
_
kinetochore
(B) In anaphase B, _ as the result of two separate forces: (1) _, and (2) _
Both forces
are thought to depend on _
the two spindle poles move apart
_
the elongation and sliding of the interpolar microtubules past one another pushes the two poles apart
_
Microtubules at the edges (astral microtubules) are pulled toward the cell edges dragging the two poles apart.
_
the action of motor proteins associated with the microtubules.
The nuclear envelope
breaks down and re-forms during mitosis. The _ of _ and _ helps trigger the disassembly of the nuclear envelope at _. _ of these proteins at telophase helps reverse the process.
phosphorylation
_
nuclear pore proteins
_
lamins
_
prometaphase
_
Dephosphorylation
