Mitosis Flashcards
What are the stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
How is Mitosis regulated?
MPF phosphorylates Aurora kinase, which phosphorylates Polo-like kinase
What four things happen as a result of MPF activation?
Chromatin condensation
Nuclear envelope breakdown
Fragementation of the Golgi
Spindle formation
What are the features of prophase?
Chromosome condensation
Nuclear envelop breakdown
Spindle formation begins
What is cohesin?
multi-subunit complex that maintains linkage of newly synthesized sister chromatids
adhere along full length of the chromosome during S phase
What is Condensin?
Promotes condensation in a process that requires ATP
Target of MPF and Aurora B
Contains proteins related to cohesion
What happens to cohesin during prophase?
Removed from most of the lingth of the chromosome arms, but remains at the centromere
At the same time condensin begins to condens the chromosome
How does the nuclear envelope breakdown and what does it allow?
Lamins depolymerize when they are phosphorylated by MPF
Membrane proteins and Lamin B diffuse to ER, Lamin A and C disperse to the cytoplasm
Allows chromosome segregation by giving the spindle access to chromosomes
What occurs during prometaphase?
Spindle formation and the attachment of chromsomes to the kinetochore
What are the four types of Microtubules?
Kinetochore - attaches to kinetochores
Chromosomal - attaches to chromosome ends
Polar (Inter) - Separates poles
Astral - position and orient spindle
What are Microtubule associated proteins (MAPs)?
Regulate assembly and disassembly of microtubules
What are Dynein and Kinesin?
Motor proteins associated with microtubules
What are centromeres?
Repetitive DNA sequences where the spindle fibers connect.
What is the Kinetochore?
Protein complex that binds centromere and spindle microtubules
What is Histone H3-like centromeric protein (CENP)?
Bind DNA and kinetochore proteins for attachment of mitotic spindle
What is CENP-E?
A Tension sensor protein that transmits information about microtubule attachment to regulatory complex
What is the Mitotic Checkpoint Complex?
Formed at unattached kinetochore and inhibits APC
Cdc20 is a part of this complex
What is Cdc20?
A required activator of APC
Activity blocked when part of MCC
What occurs when all chromosomes are properly oriented?
The MMC dissociates and APC is no longer inhibited, allowing it to trigger transition into anaphase by causing Cyclin B degredation
What is Anaphase A?
Sister chromatid separation in anaphase
What is Anaphase B?
The separation of the spindle poles during anaphase
What does the degredation of cyclin B cause?
The beginning of the exit to mitosis
What Anaphase Promoting Complex (APC)?
Ubiquitin ligase (E3) that targets Securin and Cyclin B for degredation
What is Securin?
Protein bound to separase that inhibits its function
When it is ubiquitinated by APC, it releases separase to promote chromosome separation
How do chromsomes physically segregate?
Via movement along kinetochore microtubules mediated by dynein
What is nondisjunction?
Failure to complete chromosome segregation
Results in aneuploidy
How do spindle poles separate?
Polar microtubules slide past each other via plus end directed motor proteins (Push)
Astral microtubules move spindle pole toward cell periphery via minus end motor proteins (Pull)
What causes the beginning of telophase and cytokinesis?
Cyclin B degradation via APC causes a decrease in MPF activity
What are the features of telophase?
Nuclear envelope reassembled
Chromosomes decondense –> b/c entering G1
Formation of cleavage furrow
How does the nuclear membrane reassemble?
Decreased kinase activity and dephosphorylation by Cdc14 phosphatase promote reassembly
B lamins and inner membrane proteins bind chromatin and pull membrane around chromosomes
Lamins A and C are imported via reformed NPCs
What is the Contractile Ring?
Actin filaments attached to the plasma membrane
Bipolar myosin II interacts with the AFs in sliding mechanism to contract the ring along the cleavage furrow
How is Cytokinesis regulated?
Before Anaphase - by high MPF activity, active myosin light chain phosphatase, prevents mysoin II activation
At Anaphase - MPF activity decreases - allows activation of myosin II
During Cytokinesis - Transient increase in Ca activates MLC kinase
