The cell cycle Flashcards
What determines the frequency of cell division?
Frequency of division is regulated at the molecular level.
Specific chemical signals present in the cytoplasm drives cell division
Different types of cells divide/do not divide at their own specific frequency determined by need
Describe the cell cycle control system
Regulated by sequential events organized in a series of timings like a clock
Moderated by specific checkpoints, where the cell cycle pauses until the go ahead signal is received
This regulation happens both internally and externally
How many main checkpoints are there in the cell cycle control system?
There are three main checkpoints.
G1, G2, and M
What controls the cell cycle checkpoints?
Cell cycle checkpoints are controlled by two regulatory proteins; cyclin and cyclin-dependent kinases (CdKs)
What controls cyclin-dependent kinases activity?
The concentration of cyclin controls the presence of cyclin-dependent kinases
What is a kinase?
An enzyme (protein) that adds phosphate group(s) to proteins. Also known as phosphorylation.
What is MPF?
Maturation-Promoting Factor
A cyclin-Cdk complex that is present at the G2 checkpoint. It promotes mitotic events.
It triggers a cell’s passage past the G2 checkpoint into M phase
What is the significance of the G1 checkpoint?
For many cells it is the critical checkpoint. If a cell passes the G1 checkpoint it usually completes the division process.
If a cell does not pass the G1 checkpoint, it exits the cycle and enters G0 (non-dividing) phase
It is where DNA is checked to verify it is free from defects and can be replicated
What happens when chromosomes are improperly attached to spindles?
A internal signal is tripped and cells will not pass the M checkpoint and enter anaphase
It is very important for all chromosomes to be properly attached to the spindles microtubules at their kinetochores
This ensures that all daughter cells receive the correct number of chromosomes
What are growth factors?
Chemicals released by certain cells to stimulate other cells to divide
This is classified as an external signal for cell division
An example of this is platelet-derived growth factor-a stimulant for human fibroblasts to divide
What is PDGF?
Platelet-derived growth factor
A chemical signal released from platelets that stimulates human fibroblasts to divide
What are two external conditions that regulate cell division process?
Anchorage dependence: to divide, a cell must be attached to a substratum
Density-dependent inhibition: prevents cells from dividing to the point of overcrowding
What cells disregard both anchorage and density dependency protocols?
Cancer cells
What behaviours typify cancer cells?
-do not respond normally to body’s control mechanisms
-do not require growth factor because they make their own, or convey growth factor signal without growth factor
-have abnormal cell cycle control system
Define cancer
A group of diseases characterized by uncontrolled growth and proliferation
What is transformation in regard to cancer?
A process by which normal cells convert into cancerous cells
If these cells are not eliminated by immune system, they form tumors
What are the two forms of cancerous tumours?
Benign tumour: abnormal cells that remain at original site of division
Malignant tumour: abnormal cells that invade surrounding tissues and metastasize
Metastasis results in the exportation of cancer cells to other parts of the body.
Tumour formation > Local Invasion > Intravasation > Survives circulation > arrested at new site > extravasation > micrometastasis > metastatic colonization > clinical detection
What two methods are common in treating cancer cells?
Radiation: high-energy radiation targets and damages DNA of the cancerous cells
Chemo therapies: target cell cycle to treat metastatic cancers
