Cell Cycle II

Question 1

what are Cdks and what are they activated by?

Answer 1

they are cyclin dependent kinases; although they depend on the presence of cyclins, CAKs (Cdk-activating kinases) activate them by phosphorilating the cdk-cyclin complexx

Question 2

what 4 steps does mitosis consist of?

Answer 2

1) condensation of chromosomes
2) assembly of mitotic spindle
3) breakdown of nuclear envelope
4) attachment of chromatids to spindle

Question 3

what is condensin? what does it do?

Answer 3

it is a five subunit protein complex (2 SMC subunits and 3 non-structural maintenance of chromosomes subunits)

condensin forms a ring-like structure and uses ATP to promotor compaction and resolution of sister chromatids

Question 4

what protein is condensin related to?

Answer 4

cohesin; the protein that holds sister chromatids together

Question 5

describe the mitotic spindle

Answer 5

• its a bipolar array of microtubule proteins
• pulls sister chromatids apart at anaphase
• M-Cdk (M-cyclin-Cdk complex) triggers assembly of spindle
• At mitosis stage, microtubules get organized

Question 6

what are the 3 types of microtubules?

Answer 6

kinetochore microtubules, interpolar microtubules, astral microtubules

Question 7

what do the kinetochore microtubules do?

Answer 7

attach each chromosome to spindle pole at the kinetochore (large protein structure located at the centromere of each sister-chromatid)

Question 8

what do the interpolar microtubules hold?

Answer 8

they hold the two halves of the spindle together; plus ends of interpolar microtubules from one pole interact with plus ends from other poles

Question 9

what do the astral microtubules interact with?

Answer 9

they interact with cell cortex; they radiate outward from the poles and contact the cell cortex helping to position the spindle in the cell

Question 10

where are microtubules nucleated from?

Answer 10

a specific location called microtubule-organizing center (MTOC); microtubules grow outward form the MTOC from the plus end

Question 11

what do gamma-turcs do?

Answer 11

bind to negative ends to nucleate and elongate microtubules

Question 12

what are the two major types of motor proteins on mitotic spindle?

Answer 12

• dyneins: tends to move to center of cell; MINUS END directed
• kinesins: move to periphery of cell; PLUS END directed; has two globular heads and elongated coil-coil tails; *plays important role in chromosome separation
• the assembly and function of the mitotic spindle depends on these proteins

Question 13

what are the four major classes of motor proteins involved in spindle assembly and function?

Answer 13

kinesin-5

kinesin-14

kinesin-4,10

dynein

Question 14

what does kinesin-5 do?

Answer 14

it forces centrosomes apart

two motor domains that interact with PLUS end of anti-parallel microtubule. they move these two anti-parallel microtubules past each other to force/push the spindle poles (centrosomes) apart

*walks towards plus end - forcing centrosomes apart. (like opening elevator doors)

if no kinesin-5, then spindle collapses

Question 15

what does kinesin-14 do?

Answer 15

minus end oriented directed motor with a single motor domain

pulls poles together

Question 16

what does kinesin-4,10 do?

Answer 16

aka chromokinesins - plus directed motors; push attached chromosomes away from the pole

Question 17

dyneins

Answer 17

minus end directed motors

link plus ends of astral microtubules to actin skeleton at cell cortex

by moving toward minus end of microtubule, the dynein motors pull the spindle poles away from each other

Question 18

describe kinetochores

Answer 18

• responsible for attachment of spindle to chromosomes
• spindl microtubules are attached to each sister chromatid at the kinetochore
• this is a giant multilayered protein structure built on the chromosome
• multiple microtubules attach to kinetochore (Ndc80 complex)
• there is an exposed open end for addition and removal of tubular subunits
• removal of tubular subunits leads to force pulling on kinetochore; movement of chromosomes to pole of cell

Question 19

binding to kinetochore

Answer 19

• bipolar attachement
• formed by attaching kinetochore to microtubule on opposite side of chromosomes
• sister chromatids must attach to opposite poles of mitotic spindle (called bi-oriented)
• formation of stable attachment is detected by kinetochore by tension ( unstable connections not allowed)

Question 20

what are the 3 forces of chromosome movement?

Answer 20

• depolymerization
• microtubule flux
• polar ejection

Question 21

force one: depolymerization

Answer 21

a major force PULLS the kinetochore and chromosome TOWARD the spindle pole

depolymerization of the plus end of the microtubule drives the pulling of the kinetochore poleward

Question 22

force two: microtubule flux

Answer 22

• microtubules are moved toward spindle poles while being dismantled at minus ends
• tubulin added at plus end while being removed at minus end- interpolar microtubules
• escalator

Question 23

force three: polar ejection force

Answer 23

• kinesin-4,10 on chromosomes interact with microtubules and transport chromosomes from poles
• result in push-pull phenomenon

Question 24

what are the final steps?

Answer 24

• spindle prepared
• everything is organized
• chromosomes are attached and ready to be separated to become daughter chromosomes

*M-Cdk activates APC/C to complete mitosis; cohesin system

Question 25

what are the two types of anaphase?

Answer 25

anaphase A: chromosomes move apart (due to spindle microtubule depolymerization at kinetochore; shortening of kinetochore microtubules; movement of daughter chromosomes to poles; forces generated mainly at kinetochores) anaphase B: separations of spindle poles themselves (by kinesin-5; also dynein pulls pole apart.

Question 26

what is the final step of the cell cycle?

Answer 26

cytokinesis its the end of anaphase - first visible change in cell is the cleavage furrow - underlying the cleavage furrow is the contractile ring - composed of actin and myosin filaments - rings contract, vesicles fuse with membrane to create new membrane

Question 27

what are the 4 stages of cytokinesis?

Answer 27

1) initiation 2) contraction 3) membrane insertion 4) completion

Question 28

what does the assembly of the ring result in?

Answer 28

formation of new actin filaments depend on formin; formin is the protein that nucleates assembly of linear, unbranched actin filaments actin-myosin exerts enough force to split cell into two

Question 29

what are the 3 classes of extracellular signaling molecules that regulate cell size and number?

Answer 29

class 1: mitogens - stimulate cell division by triggering G1/S-Cdk activity class 2: growth factors - stimulate cell growth class 3: survival factors - suppress form of programmed cell death known as apoptosis

Question 30

mitogens: stats

Answer 30

cells of body only divide when they need to for this to happen, extracellular signals must be detected from mitogens examples: PDGF, EGF, EPO (erythropoietin)

Question 31

how do mitogens act? describe cell-cycle entry into S-Phase via mitogenic activation of the Ras-MAPK pahtway

Answer 31

- mitogen binds to receptor - Ras causes activation of MAP kinase cascade (mitogen activated protein kinase) - leads to increase of gene regulatory proteins including Myc - Myc promotes entry into cell cycle by increasing expression of G1 cyclins - this activates G1 Cdk-cyclins - G1-Cdk-Cyclin activates group of gene regulatory factors called E2F proteins - E2F binds to promoters of G1/S cyclin and S cyclin genes (leads to DNA transcription) - Enter into S phase of cell cycle - DNA synthesis begins *duplication of chromosomes*

Question 32

how does Rb protein fit into this?

Answer 32

Rb is a regulator E2F protein is inhibited by interaction with Rb protein shuts down entry int S phase of cell cycle **active G1-Cdk phosphorylates Rb to reduce binding to E2F

Question 33

what happens if Rb protein is not working?

Answer 33

then you would have no control in going into cell cycle and cancer can occur (retinoblastoma)

Question 34

stats about retinoblastoma protein family

Answer 34

- Rb identified through studies of inherited eye cancer in children called retinoblastoma - rare childhood tumor: 4 per million - occurs before age 2 - 95% of cases diagnosed before age 5 - Rb is tumor suppressor (inhibits cell division) - Rb prevents over-proliferation of cells - Loss of both copies of Rb genes (no Rb protein made) leads to cell and tumor proliferation of retina (no inhibition means retinoblastoma)

Question 35

speak on cancer and the cell cycle and ATM/ATR

Answer 35

- DNA damage blocks cell division - Cell cycle cannot proceed with DNA damage - DNA damage activates ATM and ATR protein kinases - these kinases associate with site of damage and phosphorylate (activate) Chk1 and Chk2 proteins (checkpoint kinase 1 and 2)

Question 36

what is the major target of these Chk1/Chk2?

Answer 36

p53 protein, which stimulates transcription of p21

Question 37

what does p21 do?

Answer 37

p21 ( a CKI) binds to G1/S-Cdk and S-Cdk to INHIBIT ACTIVITY - no cell division because there's DNA damaged, so it must be repaired this is why if the ATM/ATR systems are not working, they can cause cancer

Question 38

talk about AT

Answer 38

Ataxia telangiectasia it is a syndrome, radiation-sensitive or cancer prone in which DNA damage checkpoint is disrupted; in this case, ATM protein AT patients exhibit higher incidence of lymphoma and leukemia Ataxia - poor coordination Telangiectasia - name means small dilated blood vessels both seen in AT ATM PROTEIN IS DEFECTIVE IN AT; AUTOSOMAL RECESSIVE; NO DNA REPAIR

Question 39

AT case study

Answer 39

ATM sense DNA damage major substrates are Chk1 and Chk2 these activate p53 p53 cases cell cycle arrest and DNA repair occurs *If DNA damage is real bad then p53 causes apoptosis *whenever diagnose AT - no X-rays at all. ever

Question 40

cancer gene stats

Answer 40

Ras - mutated in 30% of cancers p53 mutated in 50% of human cancers

Question 41

what is the most important growth signaling pathway?

Answer 41

PI-3 kinase pathway PI-3 kinase adds ATP to inositol phospholipids (PIP2); activates TOR (target of rapamycin) which activates many factors for cell growth

Question 42

what are the three mechanisms to coordinate cell growth with Division?

Answer 42

1) rate of cell division determined by extracellular factor leading to cell growth 2) cell growth and division controlled separately by growth factors and mitogens 3) cell growth and division both stimulated by extracellular factor

Question 43

what is myostatin?

Answer 43

it is a factor that inhibits muscle cell growth if you knockout myostatin, mouse has a very large muscle these are being used to treat DMD