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Flashcards in Mitosis and Meiosis Deck (48)

Stages of mitosis

1. Early Prophase
2. Late Prophase
3. ProMetaphase
4. Metaphase
5. Early Anaphase
6. Anaphase
7. Telophase

Know how these stages look like under Light microscope


Early Prophase

1. Early Prophase: replicated chromosomes condense


Late Prophase

2. Late Prophase: microtubules have self assembled. Centromeres that have replicated move apart



3. 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



4. Metaphase: chromosomes are aligned along the equator forming the metaphase plate (and bipolar spindle is clear - not sure what this means)


Early Anaphase

5. Early Anaphase: cohesions degrade, sister chromatids separate resulting in daughter chromosomes moving to 2 opposite pole



6. Spindle moves further apart enhancing the separation of chromosomes



7. 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