The cell cycle: The process of cell division
The cell is always regulating itself to check progress, resources, etc.
This prevents cell death, cells getting correct genetic information, and so it doesn’t turn into cancer.
G1: The cell grows by producing more proteins and organelles.
S (Synthesis): DNA replication occurs.
Everything in the cell is duplicated, incl. nucleus, centrosomes, chromosomes, etc.
G2: The cell prepares for cell division with the appearance of centrosomes.
M: Mitosis and cytokinesis occur.
G0 (Resting phase): The cell is just living, it IS NOT preparing to divide.
G stands for:
Regulation happens ONLY in Eukaryotic cells, bacteria DO NOT have any checkpoints
They all occur late in their phase.
Checking if there is enough material and energy available (This is the most IMPORTANT)
ALSO checks if there is enough SPACE to divide
ALSO checks if the cell is in G0 or not.
Checking for ERRORS in DNA replication (Checks if S worked outright)
Checking that all chromosomes are attached to the spindles AKA see if mitosis was done properly.
G1 Errors: the cells are very small OR might be missing an organelle and therefore fuck up
G2 Errors: the cell only has a wrong genetic code
M Errors: the cell won’t have the right number of chromosomes
The level of Kinase is ALWAYS constant
The concentration of Cyclin “cycles”/changes throughout the cell cycle
Maturation promoting factor (MPF):
The combination of Kinase, Cyclin, and P gives the MOST ENERGY for mitosis.
This molecule of proteins determines if a cell is in G0 and TRIGGER cell division.
When the MPF concentration reaches certain level mitosis is ready to happen.
Apoptosis: Programmed cell death, and happens if the checkpoint doesn’t work, and the cell can turn into cancer
The period of G1, S, and G2
The DNA in the nucleus is in chromatin form AKA free-flowing
After MPF has done its job of phosphorylation:
The cyclin portion of the complex is degraded.
This means that the protein is broken up into parts that can be recycled by the cell. The kinase is not degraded but instead used again as the cell goes through another cycle of division.
A group of genes that cause normal cells to become cancerous when they are mutated.
Tumor suppressor genes:
Genes make up another group of genes that regulate cell division. Genes from this group produce proteins that signal cells when they are getting too crowded, proteins whose function is to repair DNA, and still other proteins that regulate apoptosis (preprogrammed cell death). A tumor suppressor gene called p53 causes apoptosis when the cell is worn out or when defects are detected.