cell bio chap 18

eventually, the duplicated chromosomes align at the _____ of the spindle, halfway between the 2 spindle poles, thereby forming the ______ _____. this event defines the beginning of metaphase

equator metaphase plate

the control system can transiently halt the cycle at specific transition points-in G1, G2, and M phase- if ______ or _______ conditions are unfavorable

extracellular intracellular

during the 2 "gap" phases-called G1 and G2- the cell continues to ____

grow

2 types of caspases work together to take a cell apart. _______ caspases cleave, and thereby activate, downstream _______ caspases.

initiator executioner

the period between one M phase and the next is called

interphase

mammalian fibroblasts in culture, spread out flat during _______, as a result of the strong adhesive contacts they make with the surface they are growing on - called the ______

interphase substratum

______ microtubules are shortened at anaphase B

interpolar

______ microtubules elongate in anaphase B

interpolar

in a plant: the ______ microtubules of the mitotic spindle remaining at _______ form the phragmoplast and guide vesicles, derived from the Golgi apparatus, toward the _____ of the spindle. the _____, which are filled with cell-wall material, fuse to form the growing new cell wall that grows outward to reach the plasma membrane and original cell wall

interpolar telophase equator vesicles

the phosphorylation reactions that control the cell cycle are carried out by a specific set of protein ____, while dephosphorylation is performed by a set of protein ______

kinases phosphatases

_____ microtubules are shortened at anaphase A

kinetochore

at anaphase, the sister chromatids synchronously separate and are pulled slowly toward the spindle pole to which they are attached. the ____ ______ get shorter, and the spindle poles also move apart, both contributing to chromosome segregation

kinetochore microtubules

the spindle microtubules grab hold of the chromosomes at ______, protein complexes that assemble on the centromere of each condensed chromosome during late prophase

kinetochores

during this process, the nuclear pore proteins and nuclear _____ that were phosphorylated during _______ are now dephosphrylated, which allows them to reassemble and the nuclear envelope and lamina re-form. once the nuclear envelope has re-formed, the pores pump in nuclear proteins, the nucleus ____, and the condensed chromosomes decondense into their interphase state.

lamins prometaphase expands

Fas is activated by a membrane-bound protein called Fas _____, present on the surface of specialized immune cells called ____ _____.

ligand killer lymphocytes

chromosomes line up at the spindle equator at ______

metaphase

_____ promote the production of the cyclins that stimulate cell division

mitogens

the two most dramatic events in the cell cycle are when the nucleus divides, a process called _____, and when the cell later splits in two, a process called _______

mitosis cytokinesis

which 2 processes together constitute the M phase of the cell cycle?

mitosis cytokinesis

cells that die as a result of acute injury typically swell and burst, spilling their contents all over their neighbors, a process called cell _______

necrosis

phagocytic cells engulf the apoptotic cell before it spills its contents. this rapid removal of the dying cell avoids the damaging consequences of cell _____, and it also allows the organic components of the apoptotic cell to be _____ by the cell that ingests it

necrosis recycled

during telophase, the 2 sets of chromosomes arrive at the poles of the spindle. a new ____ _____ reassembles around each set, completing the formation of _ nuclei and marking the end of mitosis. the division of the _____ begins with the assembly of the contractile ring

nuclear envelope cytoplasm

prometaphase starts abruptly with the breakdown of the _____ _____. chromosomes can now attach to spindle microtubules via their _______ and undergo active movement

nuclear envelope kinetochores

prometaphase starts abruptly with the disassembly of the ____ _____, which breaks up into small membrane vesicles. this process triggered by the ______ and consequent disassembly of nuclear pore proteins and the intermediate filament proteins of the nuclear _____, the network of fibrous proteins that underlies and stabilizes the nuclear envelope

nuclear envelope phosphorylation lamina

although cyclin concentrations increase gradually, the activity of the associated cyclin-Cdk complexes tends to switch on abruptly at the appropriate time in the cell cycle. the cyclin-Cdk complex contains inhibitory _______, and to become active, the Cdk must be ________ by a specific protein phosphatase. thus, protein _____ and phosphatases regulate the activity of specific cyclin-Cdk complexes and help control progression the the cell cycle.

phosphates dephosphorylated kinases

The cell-cycle system governs the cell-cycle machinery by cyclically activating and then inactivating the key proteins and protein complexes that initiate or regulate DNA replication, mitosis, and cytokinesis. this regulation is carried out largely through the _________ and _________ of proteins involved in these essential processes

phosphorylation dephosphorylation

by the end of anaphase, the daughter chromosomes have separated into 2 equal groups, one at each ___ of the spindle. during telophase, the final stage of mitosis, the mitotic spindle ________, and a nuclear envelope ______ around each group of chromosomes to form the 2 daughter nuclei

pole disassembles reassembles

at transition from G1 to S phase, the control system confirms that the environment is favorable for ________ before committing to DNA replication

proliferation

chromosomes attach to the mitotic spindle at ______

prometaphase

the mitotic spindle starts to assemble in ______

prophase

over the course of the cell cycle, the concentration of each type of cyclin rises gradually and then falls abruptly. the gradual increase in cyclin concentration stems from increasing ______ of cyclin genes, whereas the rapid fall in cyclin concentration is precipitated by a full-scale targeted ______ of the protein

transcription destruction

Rb is abundant in the nuclei of all vertebrate cells, where it binds to particular ______ regulators and prevents them from turning on the genes required for cell proliferation. mitogens release the Rb brake by triggering the activation of G1-Cdks and G1/S-Cdks. these complexes ________ the Rb protein, altering its conformation so that it releases its bound transcription regulars, which are then free to activate the genes required for cell proliferation.

transcription phosphorylate

cyclin concentrations are regulated by _____ and by ______

transcription proteolysis

the anaphase-promoting complex tags these cyclins with a chain of ______. proteins marked in this way are directed to ______ where they are rapidly degraded. the ________ and degradation of the cyclin returns its ___ to an inactive state

ubiquitin proteasomes ubiquitylation Cdk

at the transition from G2 to M phase, the control system confirms that the DNA is _______ and fully replicated, ensuring that the cell does not enter mitosis unless its DNA is intact

undamaged

______ of nuclear membrane first cluster around individual chromosomes and then ____ to re-form the nuclear envelope

vesicles fuse

during cytokinesis in plants, the 2 daughter cells are separated not by the action of a contractile ring at the cell surface but instead by the construction of a new ____ that forms inside the dividing cell

wall

the contractile ring of animal cells is made of ____ and _____ filaments

actin myosin

chromosomes segregate during _______

anaphase

the contractile ring is assembled at _____ and is attached to membrane-associated proteins on the cytoplasmic face of the _____ _______

anaphase plasma membrane

the abrupt degradation of M and S cyclins part way through M phase depends on a large enzyme complex called- for reasons that will become clear later- _____-______ complex (APC)

anaphase-promoting

in animals, the most common form of programmed cell death is called _______

apoptosis

chromosome c induce cell death by promoting the assembly of a large, seven-armed, pinwheel-like protein complex called an _______

apoptosome

once assembled, the contractile ring is capable of exerting a force strong enough to ____ a fine glass needle inserted into the cell before ________. much of this force is generated by the sliding of actin filaments against the myosin filaments.

bend cytokinesis

the attachment to opposite poles, called _______, generates tension on the kinetochores, which are being pulled in opposite directions.

bi-orientation

cyclins have to enzymatic activity themselves, but they need to ____ to the cell-cycle kinases before the kinases can become enzymatically active. the kinases of the cell-cycle control system are therefore known as ____-_____ _____ _____, or Cdks

bind cyclin-dependent protein kinases

a cell in the throes of apoptosis may develop irregular bulges- or ____- on its surface, but it then shrinks and condenses. the cytoskeleton collapses, the nuclear envelope disassembles, and the nuclear DNA breaks up into ______. most importantly, the cell surface is altered in such a manner that it immediately attracts _____ cells, usually specialized phagocytic cells called _______

blebs fragments phagocytic macrophages

the molecular machinery responsible for apoptosis, which seems to be similar in most animal cells, involves a family of proteases called ______

caspases

cells undergoing apoptosis die quickly and _____, without damaging its neighbors

cleanly

the sisters are held together by protein complexes called _____, which assemble along the length of each chromatid as the DNA is replicated

cohesins

whereas _____ tie the 2 sister chromatids together, ______ assemble on each individual sister chromatid at the start of M phase and help each of these double helices to coil up into a more compact form

cohesins condensins

anaphase begins abruptly with the breakage of the ____ linkages that hold sister chromatids together. this release allows each chromatid-now considered a _____- to be pulled to the spindle pole to which it is attached.

cohesion chromosome

a continuous balance addition and loss of tubulin subunits is also required to maintain the metaphase spindle: when tubulin addition to the ends of microtubules is blocked by the drug ____, tubulin loss continues until the metaphase spindle disappears

colchicine

at prophase, the duplicated chromosomes, each consisting of 2 closely related sister chromatids, _____. outside the nucleus, the mitotic spindle assembles between the 2 ______, which have begun to move apart.

condense centrosomes

when the cell enters M phase, the duplicated chromosomes condense, becoming visible under the microscope like threadlike structures. protein complexes, called ______, help carry out this chromosome condensation, which reduces _____ chromosomes to compact bodies that can be more easily segregated within the crowded confines of the dividing cell.

condensins. mitotic

once activated, ____-_____ complexes help trigger various cell-cycle event, such as entry into S phase or M phase

cyclin-Cdk

switching these kinases on and off at the appropriate times is partly the responsibility of another set of proteins in the control system- the ____

cyclins

Bax and Bak promote cell death by inducing the release of the electron-transport protein _____ _ from the mitochondria into the cytosol

cytochrome c

the new cell wall starts to assemble in the _______ between the 2 sets of segregated chromosomes at the start of _______. the assembly process is guided by a structure called the _______, which is formed by the remains of the interpolar microtubules at the equator of the old mitotic spindle.

cytoplasm telophase phragmoplast

what are the 3 main transition points during the cell cycle?

-from G1 to S phase -from G2 to M phase -during mitosis

the 5 stages in mitosis

-prophase -prometaphase -metaphase -anaphase -telophase

one particularly well-understood death receptor, called ____, is present on the surface of a variety of mammalian cell types.

Fas

mitogens act by switching on cell signaling pathways that stimulate the synthesis of __ cyclins, G1/S cyclins, and other proteins involved in DNA synthesis and chromosome duplication

G1

which 3 phases together constitute the interphase of the cell cycle?

G1 S G2

the eukaryotic cell cycle usually includes 4 phases

G1 S G2 M

another group of cyclins, called _ _____, act earlier in G1 and bind to other Cdk proteins to form _-___, which help drive the cell through G1 toward _ phase

G1 cyclins G1-Cdks S

small membrane-enclosed vesicles, largely derived from the ____ ______ and filled with polysaccharides and _______ required for the cell-wall matrix, are transported along the microtubules to the phragmoplast. here, they ____ to form a disclike, membrane-enclosed structure, which expands outward by further vesicle fusion until it reaches the plasma membrane and original cell wall, thereby dividing the cell in 2

Golgi apparatus glycoproteins fuse

G1 is the gap between _ phase and _ phase.

M S G2 is gap between S and M

different cyclin-Cdk complexes trigger differernt steps of the cell cycle. the cyclin that acts in G2 to trigger entry into M phase is called _ ____, and the active complex it forms with its Cdk is called _-___

M cyclin M-Cdk

one way in which mitogens stimulate cell proliferation is by inhibiting the __ protein

Rb

which phase does DNA replication occur in?

S phase

other cyclins called S cyclins and G1/S cyclins, bind to a disting Cdk protein late in G1 to form _-___ and ______, respectively; these cyclin-Cdk complexes help launch the S phase

S-Cdk G1/S-Cdk

yeast kinetochore binds __ microtubules

1

the activity of each of these kinases rises and falls in a cyclical fashion. some of these protein kinases become active toward the end of G_ phase and are responsible for driving the cell into S phase; another kinase becomes active just before M phase and drives the cell into _____

1 mitosis

kinetochores recognize the special ___ sequence present at the centromere: if this sequence is altered, kinetochores fail to assemble and, consequently, the chromosomes fail to ________ properly during mitosis

DNA segregate

each duplicated chromosome has _ kinetochores-___ on each sister chromatid- which face in opposite directions

2 one

human kinetochores bind ___ microtubules

20-40

at the beginning of anaphase, securin is targeted for destruction by ____- the same protein complex that marks M cyclin for degradation. once securin has been removed, separase is then free to sever the cohesion linkages

APC

the 3 mechanisms the cell-cycle control system uses to pause/halt the cycle at specific transition points: -inhibition of ___ activation delays exit from mitosis -___ inhibitors block entry to S phase -inhibition of activating ______ blocks entry to mitosis

APC Cdk phosphatase

two of the most important death-inducing family members are proteins called _____ and _____

Bax Bak

the main proteins that regulate the activation of caspases are members of the ____ family

Bcl2

the cell-cycle control system depends on cyclically activated protein kinases called ____

Cdks

the cell-control system rotates clockwise, triggering essential processes when it reaches particular transition points on the outer dial. these processes include ____ _______ in S phase and the segregation of duplicated chromosomes in _____.

DNA replication mitosis

sometimes the signal to commit suicide is not generated internally, but instead comes from a neighboring cell. others stimulate apoptosis more directly by activating a set of cell-surface receptoreproteins knows as ____ receptors

death

cell division in many animal cells is accompanied by large changes in cell shape and a ______ in the adherence of the cell to its neighbors, to the extracellular matrix, or to both. these changes result, in part, from the reorganization of actin and myosin filaments in the cell ____.

decrease cortex

at the start of mitosis, the stability of microtubules ______- in part b/c M-Cdk phosphorylates microtubule-associated proteins that influence the stability of microtubules. as a result, during _____, rapidly growing and shrinking microtubules extend in all directions from the 2 ______, exploring the interior of the cell wall

decreases prophase centromeres

in the absence of mitogens, ________ Rb protein holds specific transcription regulators in an inactive state; these transcription regulators are required to stimulate the transcription of target genes that encode proteins needed for cell _______. mitogens binding to cell-surface receptors activate intracellular signaling pathways that lead to the formation and activation of __-___ and _______ complexes. these complexes phosphorylate, and thereby inactivate, the Rb protein, releasing the transcription regulators that activate the transcription of genes required for cell proliferation.

dephosphorylated proliferation G1-Cdk G1/S-Cdk

the interactions of one centrosome with the microtubules from the other centrosome stabilizes the microtubules, preventing them from _______, and it joins the 2 sets of microtubules together to form the basic framework of the ______ _____. the 2 centrosomes that give rise to these microtubules are now called spindle ____, and the interacting microtubules are called _______ microtubules.

depolymerizing mitotic spindle poles interpolar

finally, during mitosis, the cell-cycle control machinery ensures that the ______ chromosomes are properly attached to a cytoskeletal machine, called the _____ ______, before the spindle pulls the chromosomes apart and segregates them into the 2 daughter cells

duplicated mitotic spindle

some of these executioner caspases then activate additional executioners, kicking off an amplifying, _______ cascade.

proteolytic

a crucial negative control is mediated by the ______ protein

retinoblastoma (Rb)

cohesins are thought to form large protein ____ that surround the sister chromatids, preventing them from coming apart, until the rings are broken late in _____

rings mitosis

condensins help coil each sister chromatid (each DNA double helix) into a smaller, more compact structure that can be more easily _____ during mitosis

segregated

the cohesion linkage is destroyed by a protease called ______. before anaphase begins, this protease is held in an inactive state by an inhibitory protein called ______.

separase securin

the pre-existing plasma membrane and the membrane durrounding the new cell wall then fuse, completely ______ the 2 daughter cells

separating

anaphase A and B occur ________

simultaneously

immediately after a chromosome is duplicated during S phase, the 2 copies remain tightly bound together. these identical copies-called _____ _______- each contain a single, double-stranded molecule of DNA, along with its associated proteins.

sister chromatids

at metaphase, the chromosomes are aligned at the equator of the _____, midway between the spindle poles. the kinetochore microtubules on each sister chromatid attach to ______ poles of the spindle

spindle opposite

the assembly of the highly dynamic spindle depends on the remarkable properties of microtubules. microtubules continuously polymerize and depolymerize by the addition and loss of their tubulin ______, and individual filaments alternate between growing and shrinking- a process called ____ _____

subunits dynamic instability

animal cells need signals from other cells just to survive. if deprived of such _____ _____, cells activate a caspase-dependent intracellular suicide program and die by apoptosis

survival factors

the nuclear envelope re-forms at _____

telophase

experiments show that the duplicated chromosomes are not simply deposited at the metaphase plate. they are suspended there under _____. in anaphase, this will pull the sister chromatids apart

tension