What are the four phases of the standard eukaryotic cell cycle?
The cell cycle consists of the G1 phase, S phase, G2 phase, and M phase. G1 and G2 are gap phases, S is the synthesis phase, and M is the mitosis phase.
What specific event defines the S phase?
During the S phase, DNA is replicated.
What two processes collectively make up the M phase?
The M phase consists of mitosis (nuclear division) and cytokinesis (cytoplasmic division).
What occurs during the G1 phase?
The cell synthesizes all of the proteins, ribosomes, and other machinery that it will need for the cycle.
What are the sequential stages of mitosis?
The stages are prophase, prometaphase, metaphase, anaphase, and telophase.
Who were the three scientists awarded the Nobel Prize in 2001 for their discoveries of key regulators of the cell cycle?
Leland H. Hartwell, Paul Nurse, and Timothy Hunt.
What key organism did Leland H. Hartwell use to discover cell division genes?
He used yeast to identify temperature-sensitive mutants.
How do temperature-sensitive cdc mutant cells differ from normal cells at restrictive temperatures?
While normal cells have different sizes, cdc mutant cells arrest at specific points in the cell cycle (e.g., before cytokinesis) preventing division.
What experiment demonstrated that the cell-cycle control system is conserved between yeast and humans?
A human homologue gene (Cdk1/Cdc2) was able to complement (rescue) a mutant cdc2 gene in fission yeast, restoring normal cell division.
What is the role of Cyclin in the Cdk-Cyclin complex?
Cyclin binds to the Cyclin-dependent kinase (Cdk) to activate it; without cyclin, Cdk is inactive.
How is Cdk activity terminated at the end of a specific cell cycle phase?
Cdk activity is terminated by the degradation of the cyclin protein.
What are the three main classes of cyclins required in eukaryotic cells?
G1/S-cyclins, S-cyclins, and M-cyclins.
What is the function of G1/S-cyclins?
They activate Cdks at the end of G1 and commit the cell to DNA replication.
What is the function of S-cyclins?
They activate Cdks during S phase and are required for the initiation of DNA replication.
What is the function of M-cyclins?
M-cyclins promote the events of mitosis.
In vertebrates, which Cyclin and Cdk partner form the M-Cdk complex?
Cyclin B and Cdk1.
How do cyclins affect the substrate specificity of Cdks?
Cyclins confer specificity to the Cdk/cyclin complex, determining which set of substrate proteins the Cdk phosphorylates.
What is the function of Wee1 kinase in cell cycle regulation?
Wee1 kinase places an inhibitory phosphate on the Cdk, rendering the complex inactive.
What is the function of Cdc25 phosphatase?
Cdc25 phosphatase removes the inhibitory phosphate from the Cdk, activating the complex.
What effect does a wee mutant (defective Wee1) have on cell division?
It accelerates the transition from G2 to M, resulting in smaller cells.
What triggers the final stages of cell division, distinguishing it from earlier stages?
The final stages are triggered by protein degradation rather than protein phosphorylation.
What is the Anaphase Promoting Complex (APC) and when is it activated?
The APC is a complex activated during metaphase that promotes the degradation of M-cyclin.
How does the APC/C mark M-cyclin for degradation?
The active APC/C adds a polyubiquitin chain to the M-cyclin, marking it for degradation in the proteasome.
What is the central problem a cell must solve during M phase?
To accurately separate and segregate its chromosomes into a pair of daughter nuclei.
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