Mitosis Flashcards
What “stage” of cell replication is not a part of mitosis?
Cytokinesis
What are the two key players of the G2 checkpoint?
Cdk1 and Cdc25C
What protein do Cdk1 and Cdc25C bond?
B1
What is prophase?
The start of mitosis where chromosomes condense and become visible
What is the difference between pro-metaphase and metaphase?
Pro-meta: nuclear membrane disintegrates and microtubules extend from centrosomes and attack to kinetochores
Metaphase: The Chromosomes align
What happens in anaphase?
Sister chromatids are pulled apart to opposite poles by spindle fibers
What phase of the cell cycle contains DNA replication and bringing cellular constituents to sufficient levels?
Interphase
What is the result of mitosis in terms of number and chromosome similarity?
Mitosis results in two daughter cells, each with the same number and kind of chromosome as the parent nucleus
How many mistakes does yeast make in cell replication? How does this compare to mammals?
yeast makes about 1 mistake in 100,000 divisions, the rate is higher in mammals
In what crucial checkpoint is entry into mitosis?
G2
What does the G2 checkpoint check for?
- All DNA is accurately replicated and is free of damage
- There is enough cell size/resources to complete mitosis and support the daughter cells
What is CDK1 activated by? What triggers this?
It is activated when it binds to cyclin B1 and those levels rise during G2 and peak during mitosis.
Why is CdkB1 considered cytoplasmic? What phase of cell replication is this in?
It is phosphorylated at inhibitory cites and results in rate of nuclear export greater than rate of import. This happens in interphase.
What happens to CDKB1 in mitosis?
B1 is phosphorylated and this triggers an increase in nuclear import
What binds to cdc25 and inhibits nuclear import when phosphorylated?
14-3-3
What increases the rate of import in CdC25 during mitosis?
The dephosphorylating and dissociation of 14-3-3
What does Cdc25C activate and how?
It activates CDK1-B1 by dephosphorylating CDK1 and phosphorylating B1
Why is there a dual inhibitory effect of DNA damage on Cdc 25C?
It makes a tighter checkpoint to regulate DNA damage
What are the two inhibitory effects of DNA damage on CDC25C?`
It stops the unbinding of 14-3-3 and also stops the release of PLK, which activates CDC25C
In the presence of Cdc25C - S216A, what happens to the mitotic cycle?
14-3-3 is permanently dephosphorylated and therefore never binds to Cdc25C, meaning mitosis happens constantly and prematurely
What is the role of Cyclin B1 in mitosis?
Stimulation of nuclear envelope breakdown and nuclear transport
What three phases are interphase made up of?
G1, S phase, and G2
What are the 5 phases of mitosis?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What is cytokinesis?
The splitting of the two daughter cells
What happens in prophase?
The chromosomes condense and become visible
What happens in prometaphase?
The nuclear membrane begins to disintegrate and microtubules extend from centrosomes and attach to kinetochores
What happens in metaphase?
Chromosomes align at the metaphase plate
What happens in anaphase?
Sister chromatids are pulled apart
What happens in telophase?
Microtubules disintegrate and the chromatids reach the poles of the cell
What is the mechanism of chromosome condensation in prophase?
Compaction acts on chromatin by DNA wrapping around histones
What happens to transcription during chromosome compaction?
It shuts down
What allows histones to interact with DNA?
They contain highly positively charged amino acids that bond with the DNA structure
What promotes decondensation of DNA and histones?
Acylation of positive charges
Which histone is unlike the others and links DNA between nucleosomes?
H1
What protein complex facilitates the attachment of sister chromatids?
cohesins
What are coheisins essential for and what facilitates their work?
They are essential for the alignment and segregations of chromosomes and are facilitated by ATPase
What changes does the cytosol go through in prophase?
There is an increased stability of mRNA, and new microtubules form that will become the mitotic spindle
When does prophase end?
When the nuclear envelope disperses
What happens in prometaphase?
The microtubule spindle attaches to kinetochores
What is the role of CDK1 - B1 in prometaphase?
It promotes assembly of kinetochores and controls the attachment of sister chromatids
What does the SAC do?
The spindle assembly checkpoint delays cell division until accurate chromosome segregation can be guaranteed
When is the Mitotic Checkpoint Complex (MCC) activated? What does it block?
It activates when kinetochores are not properly attached to the mitotic spindle, and blocks the cell cycle progression by inhibiting the APC - C (Anaphase promoting complex)
When does the MCC deactivate?
when all the kinetochores are stably attached
What is the metaphase process of aligning the chromosomes called?
Congression
What end of a microtubule grows more reapidly?
The (+) side
What is located on (+) and (-) sides of a microtubule?
(+) has beta - tubulin
(-) has alpha - tubulin
What is the role of microtubule polarity?
Directional transport of cellular components and proper functioning of the mitotic spindle
What did the kinetochore dynamics visualization experiment determine?
The kinetochore is the site of microtubule assembley
Why does a sister kinetochore only typically incorporate one new tubulin at a time?
Microtubules assemble at one sister kinetochore and disassembles at the other generally
What are the two hypotheses for how distance equilibrium is achieved in metaphase?
Length dependent polar ejection force
Morphogen gradient
How does the length dependent polar ejection fore work?
After attaching to kinetochores, further growth of microtubules creates a PEF (polar ejection force). The amplitude of the force decreases at longer distances (the cell equator)
How does the morphogen gradient work?
Chemical regulation
What are the two anaphase motions?
A. A distance decrease between the chromosome and the pole it faces
B. Distance increase in between the poles
What initiates anaphase?
Separase cleavage of coheisins
How long does it take to pull a chromosome to its pole destination?
15m
How do humans and animals differ in their anaphases?
In humans, there is disassembly of microtubules at both ends, and in animals it may only involve one end
What are the three main types of motor protein in a mitotic spindle?
- Myosin
- Anterograde Motor proteins
- Retrograde Motor proteins
What is the role of myosin?
It moves along actin and is crucial for muscle movement/cellular movement
What is the role of Anterograde Motor proteins?
They travel along microtubules towards the (+) end and transport cargo such as vesicles and organelles
What is the role of Retrograde Motor proteins?
They move towards the (-) end of microtubules.
How do motor proteins achieve movement?
The hydrolyzation of ATP gives energy
What is chromosome-to-pole displacement?
Minus directed motor enzymes move on the filament and drag the chromosome towards the minus sides (where the poles are). This could be couples to plus-end disassembly through microtubule depolymerases
What are the stages of telophase?
- Microtubules disintegrate
- Chromatids reach the poles, and nuclear membranes start to form
- Chromosomes start to decondense + DNA transcription
Why is cytokinesis not considered a part of mitosis?
Mitosis is the division of a cell’s nuclei, and cytokinesis is the division of cytoplasm
