Cell Cycle Regulation Flashcards
Each cell cycle is coordinated with the timing of (3)
1) DNA replication
2) Cell Division
3) Growth
What controls cell progression cycle?
Regulatory proteins
If the coordination of cell cycle phases FAILS…
Daughter cells may contain an incomplete copy of the genome or be too small (leading to cell death)
The Cell Cycle
1) G1 Phase
2) S Phase
3) G2 Phase
4) M Phase
G1 Phase
AKA “Gap 1” or Growth 1
–> Cell growth occurs and cell prepares for DNA replication
S Phase
AKA Synthesis Phase
–> Synthesis (replication) of DNA occurs
G2 Phase
AKA “Gap 2” or Growth 2
–> Cell growth occurs and cell prepares for chromosomal segregation
M Phase
AKA Mitotic Phase
–> Mitosis occurs followed by cytokinesis
G0 Phase
“Quiescent/Quiet” Phase
–> A non-dividing state: An exit from the cell cycle
Most human cells are in what phase?
G0
LOOK AT GRAPHS with the 2 lines showing total cell mass and DNA content over a cell cycle
How long does it take one cell to go through one cell cycle?
It depends on the cell type
Cells that divide frequently
Skin Cells
Cells that have the ability to divide but only do so when they must
Liver Cells
Cells that rarely/never divide past maturity
Nerve and muscle cells
Cells that stop and start dividing based on conditions
Cells involved in wound repair
What was the main research question regarding the cell cycle control system?
What tells a cell whether to progress through the cell cycle or stop?
Determining the cell cycle control system STUDY:
2 hypotheses
1) Each cell cycle EVENT triggers the next event
2) Each event in the cell cycle is driven by specific molecules present in the cell
Determining the cell cycle control system STUDY:
Experiment Design + Results
Experiment #1
–> Fused G1 cell with S cell === G1 cell entered S-phase!
Experiment #2
–> Fused G1 cell with M cell
=== G1 cell entered M-Phase (without going through S-phase first; immediately began dividing)
Determining the cell cycle control system STUDY:
Main findings + Conclusion
Fusing a G1 cell with a cell in M or S phase caused the G1 cell to initiate cell division or DNA replication
Conclusion = Diffusable molecules trigger a cell to enter a later phase of the cell cycle (induces different phases)
Cell Cycle Control System
A cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle
The cell cycle control system relies on…
Internal and External signals for regulation of the cycle at checkpoints
The cell cycle control system has two types of mechanisms:
1) Mechanisms that REPRESS cell cycle progression
2) Mechanisms that INDUCE cell cycle progression
Checkpoints
“Molecular brakes” –> Can halt the cell cycle
–> A control point where stop and go-ahead signals can regulate the cycle
Signals registered at the checkpoints indicate…
if key processes have been completed SUCCESSFULLY
and therefore, whether or not it is safe to move forward
The major checkpoints
1) G1 checkpoint
2) G2 checkpoint
3) M checkpoint
G1 Checkpoint
AKA START or Restriction Point (The most important checkpoint)
–> Checkpoint that halts or allows for progression into the S phase
–> Cell decides whether to continue on to division, delay division, or enter G0 state
G1 Checkpoint checks for (4):
Checks for FAVORABLE CONDITIONS
1) Cell size
2) Nutrient/Energy (does cell have what it needs to divide?)
3) Growth Factors (Molecular signals)
4) DNA integrity
If the cell receives a GO-AHEAD signal at G1 checkpoint…
The cell WILL DIVIDE: It has committed to dividing
–> No matter whether it gets delayed in subsequent or whether it is successful or not, the cell will progress to division
–> Only way out: APOPTOSIS
If the cell does NOT receive a GO-AHEAD signal at G1 checkpoint…
The cell will enter the G0 state (exits the cell cycle)
G2 Checkpoint
“DNA Damage” or “ENTER M-Phase” Checkpoint
–> The point between G2 and M phase: Can delay the progression into mitosis if needed (if DNA errors are found)
G2 Checkpoint Checks for (2):
Any issues with the DNA:
1) DNA Damage
2) DNA replication completeness
The G2 checkpoint will HALT the cell cycle if…
DNA damage is found
–> Will not proceed until repairs are made
The G2 checkpoint will progress the cell cycle if…
No errors in the DNA are found
–> Pushing the cell into the M-Phase
If DNA errors are irreparable, what occurs at the G2 checkpoint?
The cell may induce apoptosis
The “question” G2 checkpoint asks the cell
Are you ready for mitosis?
The “question” G1 checkpoint asks the cell
Are conditions favorable and appropriate to begin cell division process?
