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What are the three key
transition points in the cell cycle? Between which phases of the cell
cycle is each transition point? (Fig. 19.32)
Know that progression through these
transition points is driven by appropriate levels of cyclin proteins and the
activity of cyclin-dependent kinases. (Slide 3)
- •Cyclin-dependent kinases (Cdks) phosphorylate
- target proteins only when bound to a Cyclin protein.
- Different Cdks & Cyclins are active at
- different points in the cycle (e.g. mitotic cyclin
- and cdk, G1 cyclin and cdk)
What is Rb? What is its
role in the restriction point control? (Slides 6-8)
- Retinol blastoma protein
- G1 Cdk-Cyclin regulates
- progression through the Restriction Point by phosphorylating the Rb protein
- Phosphorylated Rb releases E2F (a
- transcription factor), which initiates transcription of genes needed for entry
- of S phase
What are the three types
of checkpoint controls? What cellular conditions does each monitor, and at
which phase of the cell cycle does each checkpoint take place? (Slide 9)
- Replication Checkpoint
- –Final dephosphorylation to activate mitotic Cdk-cyclin is inhibited if DNA
- synthesis is incomplete
- Spindle Checkpoint
- –Anaphase promoting complex is inhibited if chromosomes are not
- attached to spindles
- –Cell cycle is halted by inhibiting different Cdk-cyclin complexes if there
- is DNA damage.
What is p53?
- protein, the “guardian of the genome,” plays a central role in DNA damage
- p53 also stimulates production of enzymes involved in
- DNA repair. But if the damage cannot be repaired, p53 activates genes needed to
- trigger cell death by apoptosis
- Bcl-2 is an inhibitor of apoptosis.
Know that p53 is phosphorylated
when there is DNA damage. Phosphorylated p53 acts as a transcription factor and
lead to production of proteins/enzymes that eventually led to 1) cell cycle
arrest 2) DNA repair 3) apoptosis. (Slide 10)
What are growth factors?
Know that when growth factor
signaling pathways are activated, apoptosis is inhibited and cell proliferation
- •Normal cells only
- continue through the cell cycle if they are exposed to the correct protein growth factors to stimulate
- signaling pathways.
- •Growth factors
- control the rate of cell proliferation and are also called mitogens.
What is apoptosis? What
cellular changes take place when a cell undergoes apoptosis? How does
apoptosis differ from necrosis? (Slides 14-15)
- Apoptosis:Programmed Cell Death
- in development and is used to get rid of infected cells or cells with DNA
- regulated process compared to the uncontrolled process of necrosis.
What can trigger
apoptosis? Regardless of which triggering event, they all lead to the
activation of a series of enzymes called __________. (Slide 16)
- –Proteolytic enzymes are
- activated and cleave nuclear lamina, cytoskeleton, and other proteins
- fragmentation occurs (by apoptosis-specific DNase)
- cells shrink and dismantle into apoptotic
- bodies which are then phagocytosed
- proceeds through the activation of a series of enzymes called caspases