Cell Division and Death Processes and Figures Flashcards
Major events of the cell cycle
The major chromosomal events of the cell cycle occur in S phase, when the chromosomes are duplicated and M phase, when the duplicated chromosomes are segregated into a pair of daughter nuclei (in mitosis) after which the cell itself divides into two (cytokinesis)
The events of eukaryotic cell division as seen under a microscope
The four phases of the cell cycle
A comparison of the cell cycles of fission yeasts and budding yeasts.
A. fission yeast typical cell cycle
B. budding yeast does not have a normal G2 phase
The behavior of a temperature-sensitive cell-division cycle Cdc mutant
A. At the permissive low temp, the cells divide normally
B. On warming to high temp, the mutant cells continue to progress through the cycle until they come to the specific step that they are unable to complete. Because the Cdc mutants still continue to grow, the become abnormally large.
**Cdc mutants identified by
Oocyte growth and cleavage in Xenopus
The oocyte grows without dividing for many months in the ovary of the mother frog and finally matures into an egg. Upon fertilization, the egg cleaves very rapidly–initally at a rate of one division cycle every 30 min–forming a multicellular tadpole within a day or two. The cells get progressively smaller with each division and the embryo remains the same size. Growth starts only when the tadpole begins feeding. The drawings in the top row are all on the same scale.
Studying the cell cycle in a cell-free system
Gentle centrifugation is used to break open a large batch of frog eggs and separate the cytoplasm from other cell components. The undiluted cytoplasm is collected, and sperm nuclei are added to it, together with ATP. The sperm nuclei decondense and tehn go through repeated cycles of DNA replication and mitosis, indication that the cell-cycle control system is operating in the cell-free cytoplasmic extract
Labeling of S-phase cells.
An immunofluorescence micrograph of BrdU-labeled epithelial cells of the zebrafish gut. The fish was exposed to BrdU, after which the tissue was fixed and prepared for labeling with flurorescent anti-BrdU antibodies (green). All the cells are stained with a red fluorescent dye.
**newly synthesized DNA
Analysis of DNA content with a flow cytometer
shows typical results obtained for a proliferating cell population when the DNA content is determined by flow cytometer - flourescnece activated cell sorter (FACS)
stained with a dye that becomes fluorescent when it binds to DNA so that the amount of fluorescence is directly proportionsal to the amount of DNA in each cell.
- unreplicated - G1
- replicated - G2 or M
- intermediate amount - S
larger peak means longer time spent in this phase
The control of the cell cycle
- DNA replication, mitosis, and cytokinesis
- stopped by Cdks
Cyclin-Cdk complexes of the cell-cycle control system
concentrations of cyclins cycle
Cdks are constant
Activity of Cdk activating kinase and cyclins on CDK activity
positively regulate
Regulation of Cdk activity by inhibitory phosphorylation
negative
The control of proteolysis by APC/C
APC/C is activated in mitosis by association with the activation subunit Cdc20
The control of proteolysis by SCF during the cell cycle
ubiquitin ligase SF depends on substrate-biding subunits called F-box proteins
An overview of the cell-cycle system
The core of the cell-cycle control system consists of a series of cyclin-Cdk complexes (yellow). As discussed in more detail later, the activity of each complex is also influenced by various inhibitory mechanisms, which provide information about the extracellular environment, cell damage, and incomplete cell-cycle events (top). These mechanisms are not present in all cell types; many are missing in early embryonic cell cycles, for examples
Fluorescence micrograph of a Chines hamster ovary cell stained to reveal microtubles and the MTOC
The microtubules (green) detected with an antibody to tubulin, are seen to radiate from a central point the microtubule- organizing center (MTOC), near the nucleus. The MTOC (yellow) is detected with an antibody to a protein localized to the centrosome.
Microtubules organized around the MTOC and spindle poles
( 1 ) establish an internal polarity to movements and structures in the interphase cell (left) and the mitotic cell (right). Assembly and disassembly ( 2 ) cause microtubules to probe the cell cytoplasm and are harnessed
at mitosis to move chromosomes. Long-distance movement of vesicles ( 3 and 4 ) are powered by kinesin and dynein motors. Both motors are critical in the assembly of the spindle and
the separation of chromosomes in mitosis.
Structure of tubulin monomers and their organization in microtubules
a. dimeric tubulin subunit with alpha and beta subunits
b) he organization of tubulin subunits in a micro- tubule. The subunits are aligned end to end into protofilaments, which pack side by side to form the wall of the microtubule. Structural polariy (+) end is Btubulin
Temperature affects whether microtubules (MTs) assemble or disassemble.
Rate of microtubule growth in vitro is much slower than shrinkage
observed in light microscope
Fluorescence microscopy reveals in vivo growth and shrinkage of individual microtubules.
letters mark the position of ends of three microtubules
Dynamic instability model of microtubule growth and shrinkage.
Structure of kinesin
Model of kinesin-catalyzed vesicle transport.
Kinesin molecules, attached to unidentified receptors on the vesicle surface, transport the vesicles from the (-) end to the (+) end of a stationary microtubule. ATP is required for movement.
Cytosolic dynein and the dynactin heterocomplex.
Dynein (green)-dynactin (orange)
The stages of mitosis and cytokinesis in an animal cell
Prophase: Separation of centrioles
Prometaphase: Capture of chromatids by MT
Metaphase: Stabilization of the chromosome at the cell equator
Anaphase: Movement of chromosome to the poles
High-voltage electron microscopy visualizes components of the mitotic apparatus in a metaphase mammalian cell.
(b) Schematic diagram corresponding to the metaphase cell in (a). Three sets of microtubules (MTs) make up the mitotic apparatus. All the microtubules have their (-) ends at the poles (centrosomes). Astral microtubules project toward the cortex and are linked to it. Kinetochore microtubules are connected to chromosomes (blue). Polar microtubules project toward the cell center with their distal (+) ends overlapping.
Relation of centrosome duplication to the cell cycle.
After the pair of parent centrioles (red) separates slightly, a daughter centriole (blue) buds from each and elongates. By G2, growth of the daughter centrioles is complete, but the two pairs remain within a single centrosomal complex. Early in mitosis, the centrosome splits, and each centriole pair migrates to opposite ends of the cell.
Model for participation of microtubule motor proteins in centrosome movements at prophase
(a) At prophase, polar microtubules growing randomly from opposite poles are aligned with the aid of (+) end–directed motors (orange). (b) After alignment, (+) end–directed mitotic kinesins (yellow), including the bipolar kinesin BimC, generate pushing forces that separate the poles. In addition, a (-) end–directed force exerted by cytosolic dynein (green) located at the cortex may pull asters toward the poles. Similar forces act later at anaphase.
Kinetochore proteins mediate attachment of chromosomes to microtubules
In animal cells, the kinetochore consists of an inner layer containing proteins that bind centromeric DNA and an outer layer connected to the (+) ends of kinetochore microtubules. The microtubules embedded in the outer layer extend toward one of the two poles of the cell. The outer layer and fibrous corona around the microtubule ends contain microtubule-binding proteins and motor proteins, including CLIP170, cytosolic dynein, and the kinesins CENP-E and MCAK.
Capture of chromosomes by microtubules in prometaphase
a) In late prophase, spindle microtubules probe randomly for chromosomes by alternately growing and shrinking at their distal (+) ends. (b) Some chromosomes first encounter the side ( 1 ), not the end, of a microtubule, interacting with the microtubule through proteins at the kinetochore. Kinetochore-associated (+) end–directed motor proteins (e.g., MCAK) then move the chromosome to the (+) end ( 2 ), thereby stabilizing the microtubule.
Stabilization of chromosome at cell equator
- Kinetochore dynein and kinesin at pole pull chromosome toward the pole
- chromokinesin push chromosome away from pole
- treadmilling of tubulin subunits stabilizes the length of the spindle MT
Shortening at the (+) end of kinetochore microtubules moves chromosomes poleward in anaphase A.
Model of spindle elongation and movement of poles during anaphase B
One or more
(+) end–directed spindle kinesins (orange) bind to antiparallel polar microtubules in the overlap region and then “walk” along a microtubule in the other half-spindle toward its (+) end. In cells that assemble an aster, cytoplasmic dynein, a (-) end–directed motor protein (green) anchored in the cortex of the plasma membrane, walks along astral microtubules, pulling the poles outward. Tubulin subunits are simultaneously added to the plus ends of all polar microtubules, thereby lengthening the spindle.
contractile ring
actin myosin filaments
regulation of contractile ring by the GTPase RhoA
activated by RhoGEF and inactivated by RhoGAP
active RhoaA is at future cleavage site. binds formins to promote assembly of actin filaments in contractile ring
Three current models of how microtubules of the anaphase spindle generate signals that influence the positioning of the contractile ring.
No single model explains all the observations, and it is likely that furrow positioning is determined by a como, with the importance of the diff mech varying in diff orgs.
A. astral stimulation
B. central stimulation
C. astral relaxation
An experiment demonstrating the influence of the position of microtubule asters on the subsequent plane of cleavage in a large egg cell.
control of the initiation of DNA replication
The ORC remains assoc with a rep origin throughout the cell cycle. In early G1, Cdc6 and Cdt1 assoc with the ORC. Resulting complex assembles Mcm ring complexes on adj DNA, resulting in the formation of the prereplicative complex (pre-RC). S-Cdk then stim the assembly of sev add proteins at the origin to form the preinitiation complex. DNA pol are recruited to origin, the Mcm protein rings are act as DNA helicases, and DNA unwind begins rep. S Cdk also blocks rereplication by triggering the destruction of Cdc6 and the inactivation of the ORC. Cdt1 is inact by geminin. Geminin is an APC/C target and its levels increase in S and M phases, when APC/C is inact. Thus, the pre-RC (Cdc, Cdt1, Mcm) cannot form a new pre-RC at the originis until M-Cdk is inact and the APC/C is act at the end of mitosis.
How DNA damage arrests the cell cycle in G1
When DNA is damaged, various protein kinases are recruited to the site of damage and initiate signal path that cause cell-cycle arrest. The first kinase is ATM or ATR dep on damage. Add protkin called Chk1 and Chk2 are recruited and act, results in phos of p52. Mdm2 normbinds p53 and promotes ubiquit and destruction.
Phos of p52 block deg and stimulates Tx of gene that encodes CKI protein p21. p21 binds and inact G1/S-Cdk and S-Cdk complexes, arresting cell in G1
extrinsic pathway of apoptosis
Fas ligand - Fas death receptor
assembly of DISC
activation and cleavage od procaspase-8, -10 or both
activaation of executioner caspases
The three classes of Bcl2 proteins
Note that the BH3 domain is the only BH domain shared by all BCL2 family members; mediates direct interactions between pro-apoptotic and anti-apoptotic family members
A. anti-apoptotic Bcl2 protein (Bcl2, BclXL)
B. Pro-apop BH123 protein (Bax, Bak)
C. pro-apop BH2-only (Bad, Bim, Bid, Puma, Noxa)
The role of BH123 pro-apoptotic Bcl2 proteins (mainly Bax and Bak) in the release of mitochondrial intermembrane proteins in the intrinsic pathway of apoptosis.
When activated by an apoptotic stimulus, the BH123 proteins aggregate on the outer mitochondrial membrane and release cytochrome c and other proteins from the intermembrane space into the cytosol by an unk mech.
How pro-apoptotic BH3-only and anti-apoptotic Bcl2 proteins regulate the intrinsic pathway of apoptosis
No stimulus: anti-apop bund to/inhibit BH123
Stimulus: BH3-only proteins are activated and bind to anti-apop so that BH123 is not inhibited
BH123 aggregate in the outer mitochondrial membrane and promote release of intermembrane mitochondrial proteins in the cytosol. anti-apop Bcl2 are bound to mitochondrial surface
Survival Factors inhibition of apoptosis
A. increased production of anti-apoptotic Bcl2 protein
B. inactivation of pro-apoptotic BH3-only Bcl2 protein
C. inactivation of anti-IAPs
