Topic 14 Cell Division

Cell cycle

Ordered series of event, cell growth and division, DNA replication, duplication of organelles/macromolecules, chromosome segregation, M phase and Interphase

Cell cycle control system

complex system, regulatory proteins, coordinate cell cycle, Feedback regulation

M (mitotic) phase

Mitosis and Cytokinesis

Interphase phase

G1 phase, S phase, G2 phase

Cell cycle checkpoints

Molecular brakes, if replication slowed - mitosis delayed, DNA damaged interphase extended, Late G1, Late G2/Early M, Midway through mitosis

Mitosis

Divison of nucleus, DNA splitting, part of M phase

Cytokinesis

division of cell, cut cell in half, part of M phase

Interphase processes

Transcription of genes, synthesis of proteins, Growth, organelle duplication

S phase

DNA replication, part of Interphase, ORC bound origins, recruits Cdc6 to position helicase, S-Cdk signal DNA replication initiation, prevents re-replication by phosphorylatin Cdc6/ORC

Late G1 checkpoint

Environment is favourable (nutrients/space/pH/energy) for proliferation

Late G2/early M checkpoint

Check DNA undamaged and fully replicated

Midway through Mitosis (Metaphase) checkpoint

Duplicated chromosomes properly attached to mitotic spindle (aligned at metaphase)

Cell Cycle Kinases/ Cyclin dependent protein kinases(Cdks)

Cyclically activated protein kinases, phosphorylation(activation) followed by dephosphorylation (inactivation), proteins that initiate/regulate DNA repliation/mitosis/cytokinesis

Cyclin

protein, Binds Cdks to activate, concentration varies based cell cyclephase, controlled by Transcription(up concentration) and Proteolysis (lower concentration)

Cycline types

M - forms M-Cdk complex, G1/S - forms G1/S-Cdk complex, S - S-Cdk complex

M cyclin

forms M-Cdk complex, trigger entry into M phase, degraded based APC/C activation

G1/S cyclin

froms G1/S-Cdk complex, initiate cell cycle

S cyclin

forms S-Cdk complex, initiate S phase, degraded based APC/C activation, prevents rereplication by phosphorylation Cdc6/ORC

Anaphase promoting complex or cyclosome (APC/C)

activation degrades M and S cyclin

Inhibitory phosphates

part Cyclin-Cdk complex, dephosphorylation activates Cdk, phosphatase removes phosphate from inactive Cdks, specific order

G1 Phase

metabolic activity/growth/repair, Intra(size/condition)/extra(enviro) cellular signals, mitogens (other cell telling to divide), decide to stay G1/into G0/enter S, activate Cdk complexes

p53 protein

DNA damage triggers, inactivate G1/S and S Cdk complexe, prevent S phase until repaired

G2 phase

growth/repair/less metabolic activity, incomplete replication/error delay M phase, M-Cdk complex activated by phosphatase

M phase

segregation of chromosomes, M-Cdk trigger entry into, prepares chromosomes, induce mitotic spindle assembly, activation through feedback, turns on APC/C (its inactivator)

Sister chromatids

identical copies of chromosome, held together by cohesion

Cohesion

protein complexs, hold sister chromatid togeteher

Chromosome condensation

pack chromatid into compact structures, partial removal of cohesion (room for condensions)

Condensins

Protein complexs, carry out chromosome condensation

Before Mitosis

DNA replication (S phase), Centrosomes duplicated triggered by G1/S-Cdk and S-Cdk, Aster and dynamic instability

Aster

radial array of microtubules

Dynamic instability

microtubules grow/shrink based addition/removal of tubulin dimers

Microtubules types

Kinetochore, Non kinetochore(interpolar), Astral

Kinetochore microtubules

important in chromosomes segregation, comes out of centromeres

Non-kinetochore (interpolar) microtubules

makes and break connection - overlap/slide past eachother, interact with motor proteins and other microtubule associated proteins, forms dense gel-like meshwork (mitotic spindle)

Astral microtubules

connect cell cortex to spindle, anchors the spindle in the cell

Kinetochores

protein complexs, assemble on centromeres of each condensed chromosomes (2 per sister chromatid),  Bi-orientation

Bi-orientation

attachment of kinetochores to opposite poles, tension pulls opposite direction, signals properly attached and ready to separate, 20-24 microtubules per kinetochores in humans

Prophase

mitotic spindles assembles, centrosomes begun to move apart

Prometaphase

breakdown of nuclear envelope, attach spindle microtubules via kinetochores

Metaphase

chromosomes align at equator, kinetochore microtubules attach sister chromatid

Anaphase

sister chromatid synchronously separate and pulled to spindle, kinetochore microtubules grow shorter, spindle poles move apart(Kinesin/Dynein), break cohesion linakges

Separase

protease, destroy cohesion linkages between sister chromatid

Securin

inhibitory protein, inactivates separase until anaphase, targeted by APC/C

Kinesin

Motor protein, act on overlapping non-kinetochores to slide past eachother

Dynein

Motor protein, associated with plasma membrane, move along astral microtubules, pull poles apart

Telophase

new nuclear envelope, formation 2 nuclei, end of mitosis, chromsomes start to decondense, cytoplasm divisions begins (Cytokinesis), assembles contractile ring

Cytokinesis - Animal cells

Contractile ring made actin/myosin filaments, cleavage furrow form perpendicular of mitotic spindle (metaphase plate) at anaphase, during anaphase overlapping microtubles recruit and activate proteins signaling ring assembly

Cytokinesis - Plant Cells

Phragmosplast assembles new cell wall from microtubule remains at equator, membrane enclose vesicles filled with glycolipid/proteins fuse to form disc (cell plate), Vesicles fuse with plasma membrane which fuses with cell wall, Cellulose fibrils to complete new cell wall