Intro to Mitosis and Meiosis Flashcards
What is the centromere?
The narrow “waist” of the duplicated chromosome where the two chromatids are closely attached
Cell Cycle
The cell cycle can be broken down into the M phase and Interphase. What is happening during each of these phases?
M phase = mitosis and cytokinesis
Interphase = G0, G1, S, G2
What is the G0 phase of the cell cycle?
After cell replicates and divides, it can exit the cell cycle to G0 where it is not actively dividing but rather just performing its function.
What is G1 phase in the cell cycle?
Cytoplasm grows, organelles are replicated, cell checkpoint where control systems in cell confirm that the environment is favorable for proliferation before committing to DNA replication
What is G2 phase in cell cycle?
Checks for errors / damage in DNA that was replicated during S phase
- What does the cell-cycle control system do?
- What is the role of cyclins?
- How are cyclins regulated?
- Switches cell cycle machinery on and off via phosphorylation/dephosporylation reactions.
- Kinases and phosphatases that control the cell cycle machinery activation are themselves activated by molecules called cyclins, which must bind to kinases/phosphatases for them to be active –> Cyclin dependent kinase (Cdk)
- Cyclins are phosphorylated in their native state, which inactivates the cyclins. A cyclin phosphatase is needed to cleave the phosphate –> cyclins activate kinases/phosphatases that phosphorylate/dephosphorylate other enzymes in cell cycle regulation
What is a mitogen?
An extracellular signal that stimultes the cell to multiply. Mitogens work to stimulate proliferation by stimulating the synthesis of large amounts of cyclins, which overcomes negative controls holding cell in arrest or in non-proliferative phase (G0)
Describe the role of p53 in cell cycle regulation.
Regulates checkpoint between G1 and S. If DNA is damged, p53 regulates transcription of Cdk inhibitor protein p21 (upregulates). P21 binds to cyclin-dependent kinases and prevents them from functioning so cell remains in G1 phase. If damage can be fixed, then it is, if it is too severe p53 can signal apoptosis.
Describe prophase of mitosis.
- Mitotic spindle forms between two centrosomes
- Microtubules of centrosome extend throughout the cell, growing and shrinking (dynamic instability), some come in contact with microtubules from other centrosome –> stabilizes mitotic spindle
- Chromatin begins to condense
- Kinetochores form at centromeres of chromosomes
Describe prometaphsae of mitosis
- Breakdown of nuclear envelope
- Chromosomes can now be attached to microtubules that come in contact with their kinetochore (protein complex that recognizes sequence of DNA at centromere of chromosomes)
Describe metaphase of mitosis.
- Chromosomes are aligned at equator of dividing cell, midway between spindle poles
- Kinetochores of each sister chromatid are attached to microtubules of opposite poles of spindle
Describe anaphase of mitosis
- Cohesin linkages holding sister chromatids together are broken –> chromosomes can now be pulled to opposite poles
- Kinetochore microtubules shorten (depolymerization of tubulin) and spindle poles move apart –> segregation
Describe how cohesin linkages are broken during anaphase.
Separase enzyme degrades cohesin molecules. Prior to anaphase, this protease is inactive but signaling during anaphase leads to activation of this enzyme and so it is free to degrade linkages between cohesin and chromosomes.
Describe telophase of mitosis.
Mitotic spindle dissassembles, nuclear envelope reforms to form two new nuclei
Describe the process of cytokinesis
Process by which cytoplasm is cleaved in two
End of M-phase of cell cycle
Utilizes contractile ring - transient structure based on actin and myosin filaments that pull the sides of the cell together to pinch off into 2 separte cells
