Mitosis and Meiosis

Question 1

Stages of mitosis

Answer 1

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

Question 2

Early Prophase

Answer 2

1. Early Prophase: replicated chromosomes condense

Question 3

Late Prophase

Answer 3

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

Question 4

Prometaphase

Answer 4

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

Question 5

Metaphase

Answer 5

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

Question 6

Early Anaphase

Answer 6

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

Question 7

Anaphase

Answer 7

6. Spindle moves further apart enhancing the separation of chromosomes

Question 8

Telophase

Answer 8

7. Telophase: daughter nuclei go apart

Question 9

What are the characteristics of tubulin growth

Answer 9

Combines with GTP, actively polymerizes, if not bound to GTP depolymerizes and kinks

Question 10

What are the subunits that make tubulin

Answer 10

Alpha and beta tubulin make the long fiber, gamma tubulin is at the centrosome and stabilizes tubulin at the negative end

Question 11

What are the features of the process of tubulin polymerization

Answer 11

The process is very dynamic, there are proteins that either stabilize or destabilize tubulin

Question 12

What are centrosomes

Answer 12

Microtubule organizing centers

Question 13

What does tubules from the centrosomes do

Answer 13

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

Question 14

What are the fibers called in kinetochore

Answer 14

K fibers or kinetochore fibers

Question 15

What other fibers are involved in this process

Answer 15

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

Question 16

Name the 3rd fibers involved here in metaphase

Answer 16

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

Question 17

What are gamma tubulesin turn stabilized by

Answer 17

Mt associated proteins stabilize gamma tubules

Question 18

What is the cloud space around the centrosomes

Answer 18

Pericentriolar space that have proteins that helps in the oraganization of the centrosomes and the microtubules

Question 19

When does the mother centrosome replicate

Answer 19

During interphase

Question 20

What is the function of centrosome in a terminally differentiated cell

Answer 20

It makes cilia

Question 21

How does the centrosome replicate

Answer 21

During S phase CDK2 is activated that p’s alot of stuff, causes the mother centrosome to break apart and replicate

Question 22

What is the function of pericentriolar proteins

Answer 22

It tightly regulates the centrosome function

Question 23

How are these proteins regulated

Answer 23

By p’s, protein expression and protein interaction

Question 24

What causes abnormal centrosome replication and what is the result

Answer 24

Alterations in the interacts or in the structure of pericentriolar proteins themselves can lead to abnormal centrosome replication.

Result is that it impairs mitosis.

Question 25

What are the steps when a cell has abnormal centrosome replication

Answer 25

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

Question 26

What happens if the p53 itself is messed up

Answer 26

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.

Question 27

What lies on the centromere

Answer 27

The kinetochore

Question 28

What are its 2 functions

Answer 28

It stabilizes the + end of the tubulin and binds to a specific region of the DNA called the centromere

Question 29

What is a centromere

Answer 29

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

Question 30

What are the 3 kinases that are important in the formation of mitotic spindle

Answer 30

They are Aurora Kinases A and B and Polo Like Kinases

Question 31

What are their functions

Answer 31

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

Question 32

When are these kinases found

Answer 32

Only during the M phase

Question 33

How many kinetochores are there on chromosomes

Answer 33

There are 2 kinetochores on either side of a chromosome that is supposed to be split into 2 daughter chromosomes

Question 34

What is MCC

Answer 34

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

Question 35

What is an Anaphase Promoting Complex

Answer 35

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

Question 36

What is the function of APC

Answer 36

It forms most of the spindle assembly checkpoint

Question 37

How does kinetochore send a wait signal

Answer 37

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.

Question 38

What happens to MAD2 in unattached kinetochore

Answer 38

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

Question 39

What happens to MAD2 when all the kinetochores are attached

Answer 39

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

Question 40

What is broken down when the cell enters prometaphase and who causes the breakdown of this compound

Answer 40

Cyclin A, APC

Question 41

What is broken down when the chromosomes align themselves at the equator, what breaks it down

Answer 41

Cyclin B, APC

Question 42

How are the DNA pulled apart

Answer 42

By motor proteins called kinesins and the dyenins that bind to mt and pull the DNA apart

Question 43

How is cytokinesis carried out

Answer 43

Formation of actin ring at the midbody that pinch the cell until it falls apart

Question 44

What is Taxol, what does it do?

Answer 44

It is an anticancer drug. It binds to tubulin and stabilizes it. So the cell cant seperate its DNA

Question 45

What is SAC

Answer 45

MAD2 and CDC20

Question 46

When does SAC come in to play

Answer 46

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

Question 47

What kind of DNA is in the centromere

Answer 47

Satellite DNA

Question 48

What contracts the actin ring to pinch off the cytoplasm

Answer 48

Aurora B and PLK