Topic 8: Cell Cycle Flashcards

Question

What is cytokinesis in mitosis?

Answer 1

physical separation of cytoplasm furrow: a ring of MFs and myosin II that forms to bisect the mitotic spindle actin filaments form a ring force is generated by bipolar non-muscle myosin

Answer 2

Rho --> ROCK --> phosphorylation of rMLC --> contraction myosin contraction is controlled by phosphorylation of MLC

Answer 3

small G proteins that can be activated by GEFs (GTP/GDP exchange factors) and inhibited by GAPs (GTPase activating proteins) Rho is tightly controlled by signals from spindle

Answer 4

two cells at different points were fused together when cells in G1 and S phase were fused then DNA synthesis started in G1 nucleus, therefore there are signals that promote S phase when cells in M phase and G1 phase were fused, G1 cells entered M phase, therefore there are signals that promote M phase

Answer 5

used an unfertilized frog oocyte arrested at G2 injected either mitotic cell cytoplasm (which caused cell to enter M phase) or interphase cell cytoplasm (no M phase) therefore there must be a soluble factor in cytoplasm of mitotic cells that promotes cell division

Answer 6

S. pombe is a unicellular eukaryotic yeast used to characterize enzymes that modify Cdks by phosphorylation isolated 2 types of mutants: elongated cells (deficit of Cdc25 or excess of Wee1): cells were too slow in cell division, therefore Cdc25 normally drives cell division forward small cells (deficit in Wee1 or excess of Cdc25): cells divided too quickly therefore Wee1 normal function is to slow cell division)

Answer 7

inhibitory kinase adds a PO4

Answer 8

activating phosphatase removes PO4

Answer 9

a culture of growing cells are exposed to a fluorescence dye for DNA as cells pass through a small opening the relative fluorescence is counted by the machine the amount of DNA can be determined thus the phase of the cell cycle can be determined (have they replicated DNA?) G1 = 1xDNA G2 = 2xDNA

Answer 10

controls entry into S phase activated G1-cyclin/CDK promotes entry into S phase targets --> Rb (retinoblastoma)

Answer 11

controls entry into mitosis activated by MPF (Mcyclin/CDK) target of MPF (lamins, APC, and histone H1 activate mitosis)

Answer 12

controls entry into anaphase activated by APC (anaphase promoting complex) not a cyclin/CDK

Answer 13

MPF was later refined to show that it was a dimer of a cyclin and a cyclin-dependent protein kinase (cyclin/CDK complex) cell cycle progression governed by key protein kinases in a cyclical manner these cyclical proteins (called cyclins) regulate passage through the various checkpoints involves a series of proteins being phosphorylated and dephosphorylated activation and deactivation are under the control of cyclins cyclins have cyclical expression but Cdks are always present

Answer 14

dimer of cyclin/CDK association of CDK with cyclin is necessary for activation of MPF, but it is not sufficient

Answer 15

cyclin-dependent kinase levels are consistent in cell cycle

Answer 16

levels vary throughout cell cycle regulators of CDK activity levels peak just before entry into mitosis

Answer 17

cyclins do not have enzymatic activity but must bind to kinases before they can become active heterodimer is inactive dimer only forms when a threshold of cyclin accumulates in the cell

Answer 18

association of CDK with cyclin is necessary for activity but not sufficient phosphorylation of key resides must be accomplished in order for activation of the CDK-cyclin complex

Answer 19

CDK and cyclin come together to form an inactive heterodimer cyclin activated kinase (CAK) adds one phosphate Wee1 adds two inhibitory phosphates Cdc25 removes inhibition phosphorylation by Wee1

Answer 20

passing through the restriction point commits a cell for eventual division senses the availability of nutrients, presence of growth factors, and cell size activation of G1 CDK/cyclin DNA damage, loss of adhesin and growth factor signaling all slow cell cycle

Answer 21

normally binds and inhibits E2F E2F is a transcription factor that regulates DNA synthesis Rb is a target of G1 cyclin/CDK cyclin/CDK promotes phosphorylation of Rb which inactivates it E2F is then available to trigger gene expression

Answer 22

CDK/cyclin complex - MPF M-CDK

Answer 23

phosphorylation of lamin causes NEBD in prometaphase phosphorylation of nuclear material causes nucleoli dismantling phosphorylation of condensin cause chromosomal condensation in prophase phosphorylation of Histone H1 causes chromosomal condensation phosphorylation of MAPs decreases MT stability and increases MT dynamics indirect activation of APC

Answer 24

M-CDK activates APC (anaphase promoting complex) APC acts at the metaphase-anaphase transition cohesin (complex of Smc1/Smc3/Klesin) which holds sister chromatids together needs to be broken down

Answer 25

APC induces polyubiquitination of securin (signal that causes protein degradation by proteasome) securin normally blocks separase, but now separase can cleave kleisin and allow separation APC is regulated by Mad/Bub Mad/Bub is produced by unattached kinetochores, therefore Mad/Bub inhibits APC to prevent passage in anaphase if chromatids are not all bound by MTs MT attachment inhibits Mad/Bub

Answer 26

if the signals for cell cycle progression are ignored or don't work, this can result in cancer and uncontrolled cell proliferation