chapter 18
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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