Chapter 17 Flashcards
The cell cycle
Why are there gaps between the S phase and the M phase?
The gaps between S phase and M phase are required partly to permit cells the time they need to grow and double their mass of proteins and organelles. The two gaps also provide time for the cell to monitor the internal and external environment to ensure that conditions are suitable and preparations are complete before beginning S phase and mitosis
What is Cyclin-dependent kinase (Cdk)?
A member of the family of protein kinases that have to be complexed with a cyclin protein in order to act.
What is Anaphase-promoting complex or cyclosome (APC/C)?
The ubiquitin ligase that promotes the destruction of a specific set of proteins, thereby promoting the separation of sister chromatids and the completion of M phase
What is M-Cdk?
The cyclin-Cdk complex responsible for stimulating entry into mitosis at the G2-M checkpoint
What is Cyclin?
A family of proteins that rise and fall in concentration in step with the eukaryotic cell cycle, thereby regulating the activity of the crucial protein kinases that control progression through the cell cycle
What is the Metaphase to anaphase transition?
The checkpoint in the cell cycle, where the control system stimulates sister-chromatid separation, leading to the completion of mitosis and cytokinesis
What is Cdc25?
A phosphatase which important for the activation of the M-Cdk complex
What is APC/C?
Anaphase promoting complex
What is Cdc20?
It is required for two microtubule-dependent processes, nuclear movement prior to anaphase and chromosome separation
What is Cdh1?
The CDH1 gene provides instructions for making a protein called epithelial cadherin (E-cadherin)
What is CAK?
CDK activating kinase
Part of the second step in activation of Cdk by phosphorylating threonine residue 160 in the CDK activation loop
What is CKI?
Cyclin-dependent kinase inhibitor protein?
function as tumor suppressor proteins. Are involved in cell cycle arrest and G1 phase
What is SCF?
SCF complexes are E3 ubiquitin ligases
SCF controls the transitions between G1/S and G2/M phase
What is M-cyclin?
The activation of M-Cdk begins with the accumulation of M-cyclin, whereafter Cdk1 associates with M-cyclin, resulting in M-Cdk complex
What is G1-Cdk?
Complex formed in vertebrate cells by a G1-cyclin and the corresponding cyclin-dependent kinase (Cdk)
What is G1/S-Cdk?
Complex formed in vertebrate cells by a G1/S-cyclin and the corresponding cyclin-dependent kinase (Cdk)
What is S-Cdk?
Complex formed in vertebrate cells by an S-cyclin and the corresponding cyclin-dependent kinase (Cdk).
What is G2-M transition?
The G2/M transition is a decisive point in a cell’s life cycle. The point at which, after successfully completing a second growth phase (G2 phase) following the replication of its DNA (S phase), it begins mitosis (the phase during which it physically separates itself into two daughter cells)
What is Wee1?
Wee1 is a nuclear kinase belonging to the Ser/Thr family of protein kinases in yeast
It is a key regulator of cell cycle progression. It influences cell size by inhibiting the entry into mitosis, through inhibiting Cdk1
How are the levels of cyclins regulated in comparison to the levels of Cdks during the cell cycle?
The concentrations of the cyclins rise and fall during the cell cycle whereas the concentration of the Cdks is constant throughout the cell cycle. They are regulated by transcription and by ubiquitin-mediated degradation
What mechanisms are involved in the regulation of cyclin-cdk complexes?
Regulated by phosphorylation and de-phosphorylation, and by the binding of Cdk inhibitor proteins (CKIs) and rates of synthesis and proteolysis of the cyclin subunits
How are the sister chromatids held together along their length until they separate at mitosis?
Cohesin complexes are deposited along the length of the sister chromatids during DNA replication in S phase.
Intertwining of DNA strings contributes to the cohesion.
The enzyme topoisomerase II gradually disentangles the sister chromatids between S phase and early M phase.
Dissociation of cohesion complexes from sister chromatids are also regulated by PLK1-mediated phosphorylation and removed enzymatically by separase.
What positive feedback mechanisms are involved in stimulating the M-Cdk complexes?
The activated M-Cdk complex stimulates the activity of the Cdc25 phosphatase, inhibits the activity of the Wee1 kinase, and stimulates expression of the M-cyclin subunit.
What events in the M-phase are stimulated by the M-Cdk complex?
Assembly of the mitotic spindle, bipolar attachment of the sister chromatids, chromosome condensation (by phosphorylation of condensin), nuclear envelope breakdown, and rearrangement of the cytoskeleton and Golgi apparatus.