Ch. 17 CSF

Cell Cycle control system

environment must be favorable, checks to make sure all conditions are satisfied at each point

interphase

cells usually grow in size, DNA is usually replicated

cyclin dependen protein kinases

CDK is the enzyme of the complex, by itself is inactive, binds to cyclin then becomes active

structural basis of CDK activation

tloop is pushed up when binding to cyclin, t loop is furtheer phosphorylated by kak, then is “fully activated”

Wee 1 kinase

adds inhibitory phosphates onto CDK, 2 are added onto CDK

Cdc 25 phosphatase

removes V1 kinase inhibitory phosphates

Cdk cyclin can be blockd by what

CDK inhibitors, p27/p21

progression through the cell cycle requres a cycling to bind to a CDK because

the binding of a cyclin to CDK is required for CDK activity

PP2A

• regulation of CDK, dephosphorylates CDK phosphates

• MCDK has a feedback pathway, ensures removal from anaphase into next phase

pp2a structure

catalytic subunit + regulatory subunit, and scaffold subunit

substrate specificity is highly dependent on which of these subunits of PP2A phosphatase?

regulatory subunit

positive feedback mechanisms that regulate CDK

CDK bound to cyclin, CAK + V1 phosphorylate, MCDK activates B1 and phosphorylates C25, keeps CDK continuously active, inhibits pp2a

mitotic regulatory circuit

M-Cdk and PP2A inhibit each other, both activated by positive feedback

anaphase promoting complex (APC)

APC ubiquitylates cyclin, inactivates Cdk (degrades M phase cycle)

Control of cyclin proteolysis by ubiquitine ligase

polyubiquitin chain degrades mcdk

cell cycle control system

checkpoint pathways used to avoid issues

which complex of APC/C is active in early G1?

APC/C-Cdh1

Inactivation of APC/C

Activation of APC/C is important for

Metaphase to Anaphase transition

S Phase

DNA synthesis

Replication

parent strands used as template, helicase unwinds DNA, polymerase transcribes new strands from each parent strands, semi conservative replication

pre-replicative complexes

inactive helicases that assemble at origins to unzip DNA, origins only fired once, kickstart replication

control of the intiation of replication

CDT

activation of which factor inhibits MCM2 loading onto DNA

S-Cdk

chromosome duplication

requires duplication of chromatin structure

cohesins

hold sister chromatids together in a ring, has 4 subunits SMC 1,3, SCC 1,3

• assemble along the length of each chromatid as the DNA is replicated, prevents them from coming apart

DNA catenation

intertwining of sister DNA during replication

prophase

centrosomes begin to move to opposite sides, centrosomes start to form spindle poles

prometaphase

nuclear envelope breaks off, phosphorylation of lamen kickstarts

• microtubules can make contact with kinetochores, starting to align

metaphase

two spindle poles align microtubules, and help align the chromosomes

anaphase

sister chromatids split, move to opposite poles, cell shape becomes more oval

telophase

two sets of daughter chromosomes arrive at poles of spindle, new nuclear envelope reassembles, completing formation of nuclei

• contractile ring contracts, division begins

cytokinesis

pinches down on the cell to divide it, high pressure

at the end of DNa replication, the sister chromatids are held together by

cohesins

condensins

mediate DNA condensin by forming a ring like structure and pushing DNA together (ATPase head and motor movement)

the concentration of M cyclin

falls toward the end of M phase as a result of ubiquitylation and degradation

microtubule

core structure of spindle, made of alpha and beta tubulins

mitotic spindle metaphase

tubulin subunits, astral microtubules, new microtubules put out by centrosomes to sustain cell

kinetochores connect to centrosomes by line of microtubules

bipolar mitotic-spindle

formed by hundreds of thousands of microtubules, new microtubules grow out in random directions

centrosome

give rise to nucleated sites/gamma tubulin ring complexes, put out microtubules, aplha+beta stack to form microtubules

centrosome duplication occurs

S → G2, initially together, in M they separate and ach synthesizes its own astral tubules

consider centrosome duplication cycle, is it conservative or semi conservative

semi conservative

spindle assembly requires breakdown of nuclear envelope by

disassembly of nuclear lamina, mediated by phosphorylation of lamina

dynein

minus end directed motor

kinesin 5

2 dimers of kinesin-5 tetramer move towards + end and in opposite directions and is important for bipolarity of spindle

kinesin 14

pulls poles together

kinesin 4 and 10

chromokinesins, push attached chromosome arms away from poles

how do spindles self organize

motor proteins: nucleation, then crosslinking by kinesin-5, outward push by kinesins 4/10, the focusing of pols by dynein

how do microtubules stabilize locally

Ran-GTPase signaling is highest around chromosomes between spindle poles

kinetochores

attach sister chromatids to the spindle

• large protein complexes, assemble onto your centromeres

• has microtubule attachment sites

tension sensing mechanism

depends on Aurora-B kinase

True/False: For microtubule organization in mitosis, chromosomes are not as important as centrosomes

False

The number of y-TURCs increased substantially at the beginning of mitosis and this is a part of the process called

centrosome maturation

dynamic instability in the spindle

the average life span of microtubules decreases over the cycle, but new ones are constantly being created

• cells require a lot of movement, microtubules cannot all deal with that

microtubule flux in the metaphase spindle

mictotubles themselves are pulled towards the spindle polesby depolymerization at minus ends

polar ejection force

polar wind- pushes chromosomes away from spindle poles and towards the spindle equator

sister chromatid separation at anaphase

after the perfect line, the chromosomes are split away from each other

initiation of sister chromatid separation by Anaphase Promoting Complex (APC)

APC-C: destruction of securin allows separase (protease) to cleave cohesion subunit Scc1

Separase is kept inactive due to

binding of securin

Anaphase A

chromosomes pulled to poles

Anaphase B

poles pulled closer to center, spindle poles move apart (kinesin-5)

telophase

sister chromatids all the way to the poles

contractile ring

actin, myosin filaments

RhoA (GTPase) signaling triggers

assembly and contraction of contractile ring, regulated by aurora kinase

phragmoplast

guides cytokinesis in higher plants

mitogens stimulate cell division

activates G1 progression

cell cycle checkpoints

p53, Chk1, avoids DNA damage

which CDK inhibitor’s transcription is induced by p53

p21