The Cell Cycle
- Two main stages: Interphase and Mitosis.
- G0 Phase. The phase after mitosis and it can be a “dormant” type of phase before interphase actively begins again.
Interphase.
- G1 (1st Gap) Phase. Physically grows larger and proliferates its organelles. Make a ton of shit to get ready to divide it up. Synthesize RNA and proteins. G1 Checkpoint. Make sure things are ready for DNA synthesis.
- S (Synthesis) Phase. Duplicate DNA. Duplicate centrosomes.
- G2 (2nd Gap) Phase. Grows more and makes more stuff to get ready for mitosis. G2 ends when mitosis begins. G2 Checkpoint.
Cell Cycle Regulation.
- R, Restriction Point. Major checkpoint at end of G1 prior to S.
- S phase checkpoint: CDK2 and Cyclin A.
- G2 Checkpoint: CDK1 and Cyclin B.
- M Checkpoint.
- G1 Checkpoint: CDK4 and Cyclin D; CDK2 and Cyclin E.
- Cdk. Cyclin dependent kinase. Adds phosphate to protein. Major checkpoint. If all is good, allows cell to move from G1 to S to G2 to M.
- MPF. Maturation Promotion Factor. Includes Cdk and cyclins. Allows cells to move between phases.
- p53. Protein that blocks cell cycle if DNA is damaged. If damage is real bad, causes cell apoptosis. p53 levels increased if DNA damaged; a “hold” is put and allows time for fixing DNA. p53 mutation is big factor leading to cancer.
- p27. Binds to cyclin and Cdk, blocks entry into S phase.
Mitotic Phase (Mitosis).
- Goal: divide the already duplicated DNA and divide the organelles to make two completely identical copies of the original cell.
- Mitosis is nuclear division plus cytokinesis (division of cytoplasm, organelles, and cleaving/pinching off the cell membrane to make 2 distinct and identical cells).
- Interphase. High metabolic activity. Chromatin are not distinct. A pair of centrioles have not yet been duplicated.
- Prophase. Chromatin condense and are visible = chromosomes. Nucleolus disappears. Centrioles move to opposite poles. Mitotic spindle fibers begin forming.
- Prometaphase. *Nuclear membrane dissolves. Proteins attach to centromeres (region where microtubules of spindle will attach), creating kinetochores (protein complex assoc. with centromeres).
- Metaphase. Paired chromosomes line up at the metaphasic plate.
- Anaphase. Paired chromosomes separate at kinetochores and move to opposite poles.
- Telophase. Chromatids are at opposite poles, nuclear membrane reforms, chromosomes get all loose again = chromatin. Spindle fibers disassemble/disperse.
- Cytokinesis. An actin ring forms and divides the cell.
- Chromatin = DNA + structural proteins, histones. The loose, uncondensed form of DNA.
- Chromosome = condensed form of DNA.
- Chromatid = each of a sister chromatin. One of two identical halves of a replicated chromosome. The two identical copies are joined at the centromere.
Resources.
