Mitosis and Meiosis Flashcards
Stages of mitosis
- Early Prophase
- Late Prophase
- ProMetaphase
- Metaphase
- Early Anaphase
- Anaphase
- Telophase
Know how these stages look like under Light microscope
Early Prophase
- Early Prophase: replicated chromosomes condense
Late Prophase
- Late Prophase: microtubules have self assembled. Centromeres that have replicated move apart
Prometaphase
- ProMetaphase: This marks the beginning of the break down of the nuclear envelope. This allows the spindles and the microtubules to interact with the recently condensed chromosomes
Metaphase
- Metaphase: chromosomes are aligned along the equator forming the metaphase plate (and bipolar spindle is clear - not sure what this means)
Early Anaphase
- Early Anaphase: cohesions degrade, sister chromatids separate resulting in daughter chromosomes moving to 2 opposite pole
Anaphase
- Spindle moves further apart enhancing the separation of chromosomes
Telophase
- Telophase: daughter nuclei go apart
What are the characteristics of tubulin growth
Combines with GTP, actively polymerizes, if not bound to GTP depolymerizes and kinks
What are the subunits that make tubulin
Alpha and beta tubulin make the long fiber, gamma tubulin is at the centrosome and stabilizes tubulin at the negative end
What are the features of the process of tubulin polymerization
The process is very dynamic, there are proteins that either stabilize or destabilize tubulin
What are centrosomes
Microtubule organizing centers
What does tubules from the centrosomes do
They reach out to a part of the chromosome called the centromere and they will bind to it. Several proteins are involved in this process and together with microtubules they form a kinetochore complex. This complex stabilizes the plus end of the microtubules
What are the fibers called in kinetochore
K fibers or kinetochore fibers
What other fibers are involved in this process
There are fibers called astral fibers that do not find a centromere and they keep growing and lock on to the cell’s cortex. This anchors these microtubules and allows leverage to put a force on the chromsomes in the process of pulling them apart
Name the 3rd fibers involved here in metaphase
These fibers are called Overlapping mt that grow past the equator and bind with kinesins which are the motors so they are the ones that apply the force
What are gamma tubulesin turn stabilized by
Mt associated proteins stabilize gamma tubules
What is the cloud space around the centrosomes
Pericentriolar space that have proteins that helps in the oraganization of the centrosomes and the microtubules
When does the mother centrosome replicate
During interphase
What is the function of centrosome in a terminally differentiated cell
It makes cilia
How does the centrosome replicate
During S phase CDK2 is activated that p’s alot of stuff, causes the mother centrosome to break apart and replicate
What is the function of pericentriolar proteins
It tightly regulates the centrosome function
How are these proteins regulated
By p’s, protein expression and protein interaction
What causes abnormal centrosome replication and what is the result
Alterations in the interacts or in the structure of pericentriolar proteins themselves can lead to abnormal centrosome replication.
Result is that it impairs mitosis.
What are the steps when a cell has abnormal centrosome replication
There is a centrosome checkpoint that we will later talk about. The cell makes alot of p53 which shuts down cell cycle. If the damage is too great it can lead to cell apoptosis
What happens if the p53 itself is messed up
The cell cycle wont be shut down, the cell will continue with mitosis with abnormal centrosomes and this leads to aneuploidy. Almost all solid cancers have aneuploidy.
What lies on the centromere
The kinetochore
What are its 2 functions
It stabilizes the + end of the tubulin and binds to a specific region of the DNA called the centromere
What is a centromere
It is part of the DNA that is in the center. here the histones are different such that it has nucleosomes that the kinetochore protein can latch on to. These histones are called CENPA.
Also in this region you can find the cohesion
What are the 3 kinases that are important in the formation of mitotic spindle
They are Aurora Kinases A and B and Polo Like Kinases
What are their functions
Aurora A: Localized at the centrosome
Aurora B: localized to the kinetochore/spindle midzone
Polo like kinase is at both the centrosome and the kinetochore
When are these kinases found
Only during the M phase
How many kinetochores are there on chromosomes
There are 2 kinetochores on either side of a chromosome that is supposed to be split into 2 daughter chromosomes
What is MCC
Mitotic Checkpoint Complex. When only one of the kinetochore is bound to the kinetochore proteins and starts pulling the chromosome on one side, the unattached kinetochore forms the MCC so it destabilzies the other kinetochore to stop pulling of the chromsome
What is an Anaphase Promoting Complex
It is Ubiquitin Ligase (E3). It has many factors and proteins associated with it. This proteins can be interchanged to form different forms of APC. These proteins will form APC at different times and at different cell cycles
What is the function of APC
It forms most of the spindle assembly checkpoint
How does kinetochore send a wait signal
When they are not bound to mt on one side they send out a ‘WAIT’ signal which are the MAD1 and MAD2 proteins.
MAD2 complex binds with APC and also brings with it BUBR1 and BUB3 which are a part of the MCC. This inhibits APC.
What happens to MAD2 in unattached kinetochore
MAD2 goes on and finds CDC20. It binds to the complex of APC-CDC20 and recruits BUBR1 and BUB3. This causes the APC to become inactive so it cannot degrade securin (which has to be removed to break down the cohesion complex) and cyclin B. So the cell now cannot proceed to Anaphase
What happens to MAD2 when all the kinetochores are attached
MAD2 in its open from interacts with dynin which is a motor protein and is taken all the way to centrosome so it does not inhibit APC anymore. Now even if APC is inactive due to binding of CDC20 and BUBR1 and BUB3, this complex will soon degrade making the APC active again and now the cell can go on and proceed to anaphase
What is broken down when the cell enters prometaphase and who causes the breakdown of this compound
Cyclin A, APC
What is broken down when the chromosomes align themselves at the equator, what breaks it down
Cyclin B, APC
How are the DNA pulled apart
By motor proteins called kinesins and the dyenins that bind to mt and pull the DNA apart
How is cytokinesis carried out
Formation of actin ring at the midbody that pinch the cell until it falls apart
What is Taxol, what does it do?
It is an anticancer drug. It binds to tubulin and stabilizes it. So the cell cant seperate its DNA
What is SAC
MAD2 and CDC20
When does SAC come in to play
When the kinetochore is attached to only 1 side, SAC comes in and recruits MCC which is BUBR1 and BUB3. This binds with the APC and bind it to stop it from functioning
What kind of DNA is in the centromere
Satellite DNA
What contracts the actin ring to pinch off the cytoplasm
Aurora B and PLK
