intro to cell cycle Flashcards
lecture 18
What are the different types of cell division?
Cloning cells: To make tissues.
Differentiation: Making cells of different types, often involving asymmetric divisions.
Meiosis: Producing cells with half the normal DNA content, e.g., eggs and sperm.
What is the purpose of the cell cycle?
To allow a cell to reproduce.
Why is the cell cycle important?
Required for growth, development, and procreation.
Ensures stable inheritance of cell and organism characteristics.
Must be controlled to allow development and prevent disease.
What must happen during the cell cycle?
Chromosomes are duplicated.
Organelles are copied.
Cells grow.
Chromosomes are segregated accurately.
Cells physically divide.
What are the phases of the basic cell cycle?
G1 (Gap 1): Growth and preparation for DNA synthesis.
S (Synthesis): DNA and centrosome replication.
G2 (Gap 2): Preparation for mitosis.
M (Mitosis): Chromosome segregation and cytokinesis.
G0: Resting state for quiescent, terminally differentiated, or senescent cells.
What drives the cell cycle?
Cyclin-dependent kinases (Cdks), which act as master regulators by transferring phosphate groups to their substrates.
How are Cdks activated?
By cyclin proteins, which also influence substrate specificity. Cyclin levels oscillate to regulate cell cycle phases.
How were cyclins discovered?
Tim Hunt observed cyclins in radiolabelled sea urchin egg extracts, where they appeared after fertilisation and disappeared during cell division.
What causes cyclin levels to oscillate?
Synthesis control: Changes in transcription and translation rates.
Degradation control: Degradation of M-cyclin is triggered by the APC/C (Anaphase-Promoting Complex/Cyclosome).
What is the role of the APC/C in the cell cycle?
The APC/C is a ubiquitin ligase that tags proteins like M-cyclin for degradation.
Degradation of M-cyclin ends mitosis and initiates cell division.
How is cell cycle fidelity maintained?
Cyclin oscillations provide timing for cell cycle phases.
Checkpoints monitor conditions before progression to the next phase.
What are the major cell cycle checkpoints?
**- G1-S Transition (START/Restriction Point): **Checks nutrient availability, proliferation signals, DNA repair, and duration of prior mitosis.
**- G2-M Transition: **Checks for DNA replication completion, DNA repair, and sufficient cell size.
**- Metaphase-Anaphase Transition (SAC): **Ensures proper chromosome attachment to the spindle.
What happens if checkpoints cannot be satisfied?
Cells may fix errors and resume the cycle.
If errors are irreparable, cells may:
Enter senescence: Permanently exit the cycle.
Undergo apoptosis: Programmed cell death.
What are the consequences of defective checkpoints?
**-G1 checkpoint defects: **Aberrant mitogen signalling drives uncontrolled proliferation (e.g., EGFR or Ras mutations).
**-G2 checkpoint defects: **Accumulation of DNA damage (e.g., p53 mutations).
- Mitotic checkpoint defects: Aneuploidy (e.g., BubR1 mutations causing MVA syndrome).
What phenotype is observed in cell cycle mutants (e.g., yeast)?
Mutants cannot grow or divide effectively, often leading to cell death.
