Chapter 12 - The Cell Cycle - Part 2 Flashcards
What is binary fission?
Prokaryotes can undergo a type of reproduction in which the cell grows to roughly double its size and then divides to form two cells. Binary fission refers to this process and to the asexual reproduction of single celled eukaryotes.
- The chromosomes replicate and the two daughter chromosomes actively move apart; the plasma membrane pinches inward, dividing the cell in two.
What is the origin of replication?
When the DNA of the bacterial chromosome begins to replicate at a specific place on the chromosome
How is the eukaryotic cell cycle regulated?
By a molecular control system; regulation at the molecular level.
- The frequency of cell division varies with the type of cell; i.e. gut 1x / day, liver 1x / year, brain 1x / 100 years
- Cancer cells manage to escape the usual controls of the cell cycle
What is the 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 sequential events of the cell cycle are directed by this control system and is regulated by both internal and external controls. (similar to a clock)
The clock has specific checkpoints where the cell cycle stops until a go ahead signal is received.
- This checkpoint is a control point in the cell cycle where stop and go ahead signals can regulate the cycle.
What are the 3 important checkpoints in the cell cycle control system?
The three important checkpoints are found in the G1, G2, and M phases.
What does each checkpoint monitor?
G1 - monitors cell size and DNA damage; must reach a certain size or cell with go to G0
G2 - checks that replication is complete and the number of chromosomes are correct and ready for mitosis
M - checks that spindle fibers are connected to the chromosomes
G0 - non-dividing cells; i.e. muscle / nerve cells
What two types of regulatory proteins are involved in cell cycle control?
- Cyclins - a protein that gets its name from its cyclically fluctuating concentration in the cell;
- Cyclin dependent kinases (Cdks) - enzymes that activate or inactivate other proteins by phosphorylating them; the activity of a Cdk rises and falls with changes in concentration of its cyclin partner
* The cyclin level rises during the S and G2 phases and then falls abruptly during M phase
What is MPF?
Maturation promoting factor; a cyclin-Cdk complex that triggers a cells passage past the G2 checkpoint into the M phase; the peaks of MPF activity correspond to the peaks of cyclin concentration
- Acts at the G2 checkpoint as a go-ahead signal, triggering the events of mitosis
What are the functions of MPF / the active Cdk complex? (*cyclin combines with Cdk, producing MPF)
- Breakdown of nuclear membrane
- Reorganization of cytoskeleton
- Chromosome condensation
- MPF promotes mitosis by phosphorylating various proteins
- MPF’s activity peaks during metaphase
What is the G0 phase?
Non dividing - most cells in the human body are actually in the G0 phase
What is a growth factor?
A protein released by certain cells that stimulates other cells to divide; different cell types respond specifically to different growth factors or combinations of growth factors
For many cells, which checkpoint seems to be the most important?
For many cells, the G1 checkpoint seems to be the most important; if a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide.
If the cell does not receive the go-ahead signal, it will exit the cycle and switch into the non dividing state, G0 phase.
What is density dependent inhibition?
A phenomenon in which crowded cells stop dividing
What is anchorage dependence?
To divide, cells must be attached to a substratum, such as the inside of a culture flask or the extracellular matrix of a tissue; anchorage is signaled to the cell cycle control system via pathways involving plasma membrane proteins and elements of the cytoskeleton linked to them
What is transformation?
The process that causes cells to behave like cancer cells; cells in culture that acquire the ability to divide indefinitely are said to have undergone transformation
