Lecture 29

Question 1

Define Condensin and describe it’s function

Answer 1

condesin is a 5 subunit protein complex that contains 2 SMC (structural maintenance of chromosomes) subunits and 3 non-SMC subunits

It forms a ring-like structure and uses ATP to promote compaction and resolution of sister chromatids just before anaphase begins

Question 2

Name and describe the 3 classes of microtubules

Answer 2

Kinetochore m.:

Interpolar m.:

Astral m.:

Question 3

Name and describe the attachments of the 3 classes of microtubules

Answer 3

Kinetochore m.: attach each chromosome to the spindle pole

Interpolar m.: hold the 2 halves of the spindle together

Astral m.: interact with the cell cortex

Question 4

name and describe the 3 forces that work to create chromosome movements.

Answer 4

Depolymerization: of the plus end drives the pulling of the kinetochore towards the pole

Microtubule Flux: microtubules are actively getting dismantled at their plus end (tread-milling on plus end so the length stays the same) which pulls the chromatid towards the pole

Polar ejection: kinesin-4,10 motors on chromosomes walk away from the poles (towards plus end). this action results in a “push-pull” phenomenon

Question 5

describe how the following are related. APC/c, securin, separase, cohesin.

Answer 5

once everything is prepared/organized enough for anaphase to begin, M-Cdk activates APC/C

APC/C ubiquitinates securin, which destroys it and allows separase to become active

separase cleaves the cohesin from between the sister chromatids and allows them to separate

Question 6

Describe how the following are related to cell growth. Rb, ATM, Chk1, Chk2, p53, p21 CKI.

Answer 6

Rb: is a tumor suppressing protein that inhibits the action of E2F protein (this protein triggers DNA transcription and entry into S phase)

ATM: (and ATR) is a protein kinase that is activated by DNA damage

Chk1 and Chk2: are both checkpoint kinases that are phosphorylated by (DNA damage activated) ATM

p53 protein: is a major target of phosphorylated Chk1 and Chk2. Activated p53 stimulates the transcription of p21 CKI

p21 CKI: binds to G1/S-Cdk’s and S-Cdks to inhibit the uncontrolled cell division that was caused by DNA damage

(this is all a big system to prevent cancerous growth and fix the damaged DNA)

Question 7

Describe retinoblastoma

Answer 7

it is caused by a loss/malfunction of both Rb genes, leading to uncheched cell growth in the retina

most cases are diagnosed before age5

Question 8

For Kinetochore microtubules , describe where their plus and minus ends attach.

Answer 8

The plus ends are attached to the kinetochores of sister chromatid pairs and the negative end is attached to the centrosome

Question 9

describe the direction it walks, structure, and the role kinesin-5 plays in spindle assembly.

Answer 9

it walks towards the plus end

it has 2 motor domains that interact with the plus end of anti-parallel microtubules

kinesin-5 moves these spindles past each other, in opposite directions

this “forces/pushes” the centrosomes (poles) apart from one another and to opposite sides of the dividing cell

Question 10

describe the direction it walks, and the role kinesin-14 plays in spindle assembly. explain how kinesin-5 and kinesin-14 work together

Answer 10

it walks towards the minus end

this “pulls” the poles (centrosomes) together

kinesin-5 “pushes” while kinesin-14 “pulls” the poles at the same time

this gives structural integrity to the spindle and effectively orients the poles

Question 11

Give another name for kinesin-4,10, list the direction it walks, and it’s function.

Answer 11

Chromokinesins

walks toward the plus end

pushes attached chromosomes away from the pole

Question 12

For astral microtubules , describe where their plus and minus ends attach.

Answer 12

their plus ends radiate out from the centrosome (where negative end attaches) and contact the cell cortex

Question 13

describe the 3 forces driving chromosomes movement in cell division

Answer 13

Depolymerization: of the plus end drives the pulling of the kinetochore towards the pole

Microtubule Flux: microtubules are actively getting dismantled at their plus end (treadmilling on plus end so the length stays the same) which pulls the chromatid towards the pole

Polar ejection: kinesin-4,10 motors on chromosomes walk away from the poles (towards plus end). this action results in a “push-pull” phenomenon

Question 14

Describe ataxia telangiectasia

Answer 14

Ataxia = poor coordination
Telangiectasia = small dilated blood vessels

The ATM protein is defective in pt’s with this disease, which makes them unable to repair DNA (radiation is especially bad for them)

autosomal recessive genetic condition

Question 15

How does a lack of Rb protein lead to retinoblastoma?

Answer 15

Rb protein is an inhibitor of E2F protein that stops the cell from entering into S phase

If both copies of the Rb gene are lost (no Rb protein gets made), then there is loss of cell division control and retinoblastoma occurs

Question 16

What is the Ndc80 complex on a kinetochore?

Answer 16

it is a place where multiple microtubules can connect to the same kinetochore

Question 17

why is there an “exposed end” of a microtubule that is attached to the Ndc80 complex on a kinetochore? what sort of force is generated at this “exposed end”

Answer 17

so tubulin subunits can either be added or removed as needed

“force pulling” on the kinetochore can occur here when tubulin subunits are removed from the exposed end of the attached microtubule (this moves chromosomes to the pole of the cell)

Question 18

Describe the term “bipolar attachment” when it is refering to microtubules binding to kinetochores. describe the level of stability that bipolar attachments form, and how that occurs.

Answer 18

bipolar attachment: each sister chromatid is attached to spindles that belong to opposite poles of the dividing cell

only very stable attachements are allowed to occur here, and that is mediated by “kinetochore tension”

Question 19

Describe the term “bipolar attachment” when it is refering to microtubules binding to kinetochores. describe the level of stability that bipolar attachments form, and how that occurs.

Answer 19

bipolar attachment: each sister chromatid is attached to spindles that belong to opposite poles of the dividing cell

only very stable attachements are allowed to occur here, and that is mediated by “kinetochore tension”

Question 20

Compare and contrast Anaphase A and Anaphase B.

Answer 20

Anaphase A: chromosomes move apart due to spindle microtubule depolymerization at the kinetochore

Anaphase B: separation of spindle poles themselves occurs via the action of kinesin-5 and dynein motor proteins

Question 21

Compare and contrast Anaphase A and Anaphase B.

Answer 21

Anaphase A: chromosomes move apart due to spindle microtubule depolymerization at the kinetochore

Anaphase B: separation of spindle poles themselves occurs via the action of kinesin-5 and dynein motor proteins

Question 22

Name the 4 stages of cytokinesis in order

Answer 22

Initiation

Contraction

Membrane insertion

Completion

Question 23

Name the 4 stages of cytokinesis in order

Answer 23

Initiation

Contraction

Membrane insertion

Completion

Question 24

In terms of the role of ATM protein, relate what does not occur in pt’s with Ataxia telangiectasia

Answer 24

ATM senses DNA damage and acts of Chk1 and Chk2

Chk1 and Chk2 activate p53, which arrests the cell cycle

if the DNA damage is mild, repair occurs BUT p53 can trigger apoptosis if the DNA damage is severe

(ATM doesn’t work so none of this happens in AT patients)

Question 25

In terms of the role of ATM protein, relate what does not occur in pt’s with Ataxia telangiectasia

Answer 25

ATM senses DNA damage and acts of Chk1 and Chk2

Chk1 and Chk2 activate p53, which arrests the cell cycle

if the DNA damage is mild, repair occurs BUT p53 can trigger apoptosis if the DNA damage is severe

(ATM doesn’t work so none of this happens in AT patients)

Question 26

In the PI-3 kinase pathway, what 2 substances must be present in order to activate the pathway and trigger cell growth?

Answer 26

nutrients and growth factors

Question 27

Explain the PI-3 kinase pathway

Answer 27

in the presence of nutrients and growth factors, PI-3 kinase adds ATP to PIP2

PIP2 then activates TOR (target of rapamycin)

Activated TOR activates many factors for cell growth

Question 28

Describe the 3 mechanisms to coordinate cell growth with division in a cell (extracellular factor, cell growth, cell division)

Answer 28

the rate of cell division is determined by an extracellular factor leading to cell growth

Cell growth and division are controlled separately by growth factors and mitogens

Cell growth and division are both stimulated by an extracellular factor

Question 29

Define “density dependent inhibition of cell division” and how that related to mitogens effect on cell growth

Answer 29

density dependent rate of cell division: describes the phenomenon that occurs when a cell culture in a dish senses that there is no more room in the environment to further divide, and accordingly stops cell growth/division

mitogens being depleted in the environment are how the cell senses that it must stop dividing

if you were to add more mitogen to the culture, the cells would begin to divide again, despite the consistent volume of the dish

Question 30

what does myostatin do? what happens if you knockout the myostatin gene of an organism?

Answer 30

it inhibits muscle cell growth

knocking out the myostatin gene will remove it’s inhibition and cause large muscles