Cell Cycle regulated by a molecular control system
The timing and rate of cell division in different plants and animals are crucial to:
Normal growth, development and maintenance
Human skin cells
Divide frequently
Liver cells
Divide if necessary Ex. To repair wound or damage tissues
Fully formed nerve cells and muscle cells in mature humans
Do not divide at all
Cell cycle differences result from
Regulation at the molecular level
Understanding of the mecanisms
The life cycle of normal cells and how cancer cells manage to escape the controls
Growth factors are generally called
Human Growth Hormone
Lack of HGH
Dwarfism
Too much of HGH
Gigantism
How many growth factors are already discovered
50
These are proteins secreted by certain body cells that stimulate other cells to divide
Growth factors? (not sure)
Different type of cell respond specifically to certain growth factors
True
Different types of cell does not respond specifically to certain growth factors
False
These cells (animal cells), do not divide unless they are signaled by a certain ___ that leads to undergo the process of cell cycle
Growth factor
Crowding of cells
Inhibit cell division
The sequential events of the cell are directed by a distinct
cell cycle control system
Three important checkpoints
G1 phase, G2 phase, M phase
Is cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle
Cell cycle control system
Things to consider in Checkpoints (red)
Size of cell, crowding of cells, wounded/dead cells
In mitosis, the daughter cells produced should be an exact duplicate of the parent cell
.
Mistakes in the duplication will lead to mutation and cells may become abnormal and may be passed on to the next generation
.
G1 checkpoint
Determines whether all conditions are favorable for cell division to proceed
G1 (2)
Also called the restrict point(in yeast) is a point at which the cell irreversibly commits to the cell division process
G1 (3)
-The most importantly checkpoint
-Is the cell big enough to divide
-Does the cell have adequate energy to proceed
-is there no damage in the dna
-are enzymes and proteins available for the S phase?
What will happen if the cells does not meet all the requirements?
Halt and try to solve the problem, cell proceeds to G0 and awaits the signal
G2
Ensures that all chromosomes have been replicated and dna is not damaged
If certain conditions are not met in the mitotic phase what will happen?
Bars entry into the mitotic phase
If the checkpoint in G2 detects problems with the DNA, the cell is___ and the cells attempts to _____ dna replication or _____ the damaged dna
Halted, complete, repair
M phase
-Occurs near the end of the metaphase stage of karyokinesis
M phase (2)
Also known as spindle checkpoint, because it determines whether all sister chromatids are connected to the spindle microtubules
The cycle in M phase will not proceed until the___
Kinetochores of each pair of sister chromatids are anchored to at least two spindle fibers from the opposite poles of the cells
What are the molecules that control the cell systen
Cyclin and Cyclin-dependent kinases
The most common molecules involved in regulating the cell cycle are
Cyclin and Cyclin-dependent kinases
A group of related proteins among the most important core cell cycle regulators
Cyclin
G1 cyclins
Cyclin D
G1/S cyclins
Cyclin E
S cyclins
Cyclin A
M cyclins
Cyclin B
Each cyclin is associated
Particular phase, transition, or set of phases in the cell cycle and helps drive the events of that phase or period
Cyclin dependent kinases
To drive the cell cycle forward, a cyclin must activate or inactivate many target proteins
Cyclins drive the cell cycle events by partnering with a family of enzymes called the __
Cyclin dependent kinases
A lone cdk is inactive, but the ___ activates it
Binding of a cyclin
Are kinases, enzymes that phosphorylate specific target proteins
Cyclin dependent kinases
When a cyclin attaches to a Cdk, it has two important effects appropriate to the cell cycle period controlled by cyclin
-it activates the cdk as a kinase
-directs the cdk to a specific set of target proteins
MPF
Maturation-promoting factor
A cyclin-CDK complex
MPF
We often think MPF as ___ because it triggers the cell's passage into the M phase, past the G2 checkpoint
M-phase-promoting factor
When cyclins that accumulate during G2 associate with CDK molecules, the resulting MPF complex is __
Active
Second group of cell cycle regulators are
Negative regulators
Negative regulators ___ the cell cycle
Halt
In positive regulation, active molecules cause the cell cycle to
Progress
The best understood negative regulatory molecules are
Retinoblastoma protein, p53, p21
Are a group of tumor-supressor proteins common in many cells
Retinoblastoma proteins
Refer to the functional molecular masses of the proteins (p) in kilodaltons
P53, p21
What is known about the cell cycle regulation comes from __
Research conducted with cells that have lost regulatory control
All three of these regulatory proteins were discovered to be damaged or non-functional in cells that had begun to replicate uncontrollably
(becomes cancerous)
Main cause of the unchecked progress throught the cell cycle was a ___
Faulty copy of the regulatory protein
3 signals
First, cyclin+cdk signal to proceed and divide
Second, p53, p21 and Rb signal to stop
Third, time point
Give signal, proceed in the cell cycle and halt the cell cycle
Protein
Positive signal
Cell divides
Negative signal
Cell will stop dividing
There are specific proteins are responsible for signaling the cell to proceed or stop dividing
Signals
Proceed
Cyclins, cylin dependent kinases, phosphatase
Stop
Dna is damaged the cell will not divide, p53, p21, Retinoblastoma protein
What will happen if the check point loses control?
Cancer
A cell cycle disease
Cancer
Do not follow the normal signs that regulate the cell cycle
Cancer cells
Divide excessively and may invade other tissues of the body
Cancer cells
If cancer cells are unchecked
They continue to grow and kill organisms