Kapitel 17 Flashcards by Stefan Fridlund

hase

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Stage of mitosis during which chromosome segregation occurs as chromosomes move toward the two spindle poles.

anaphase A

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Stage of mitosis during which chromosome segregation occurs as spindle poles separate and move apart.

anaphase B

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Ubiquitin ligase that catalyzes the ubiquitylation and destruction of securin and M- and S-cyclins - initiating the separation of sister chromatids in the metaphase-to-anaphase transition during mitosis.

anaphase-promoting complex (APC/C; cyclosome)

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In the mitotic spindle - any of the microtubules radiating from the aster which are not attached to a kinetochore of a chromosome.

astral microtubule

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Protein kinase activated by double-strand DNA breaks. If breaks are not repaired - ATM initiates a signal cascade that culminates in cell cycle arrest. Related to ATR.

ATM (ataxia telangiectasia mutated protein)

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Protein kinase activated by DNA damage. If damage remains unrepaired - ATR helps initiate a signal cascade that culminates in cell cycle arrest. Related to ATM.

ATR (ataxia telangiectasia and Rad3 related protein)

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The attachment of sister chromatids to opposite poles of the mitotic spindle - so that they move to opposite ends of the cell when they separate in anaphase.

bi-orientation

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A four-chromatid structure formed during meiosis - consisting of a duplicated chromosome tightly paired with its homologous duplicated chromosome.

bivalent

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Activating subunit of the anaphase-promoting complex (APC/C).

Cdc20

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Protein phosphatase that dephosphorylates Cdks and increases their activity.

Cdc25

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Protein essential in the preparation of DNA for replication. With Cdt1 it binds to an origin recognition complex on chromosomal DNA and helps load the Mcm proteins onto the complex to form the prereplicative complex.

Cdc6

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Activating subunit of the anaphase-promoting complex (APC/C).

Cdh1

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Protein that binds to and inhibits cyclin–Cdk complexes - primarily involved in the control of G1 and S phases.

Cdk inhibitor protein (CKI)

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Protein kinase that phosphorylates Cdks in cyclin–Cdk complexes - activating the Cdk.

Cdk-activating kinase (CAK)

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Protein essential in the preparation of DNA for replication. With Cdc6 it binds to origin recognition complexes on chromosomes and helps load the Mcm proteins on to the complex - forming the prereplicative complex.

Cdt1

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Reproductive cycle of a cell: the orderly sequence of events by which a cell duplicates its chromosomes and - usually - the other cell contents - and divides into two. (Figure 17–4)

cell cycle (cell-division cycle)

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Flattened membrane-bounded structure that forms by fusing vesicles in the cytoplasm of a dividing plant cell and is the precursor of the new cell wall.

cell plate

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Network of regulatory proteins that governs progression of a eukaryotic cell through the cell cycle.

cell-cycle control system

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X-shaped connection visible between paired homologous chromosomes during meiosis. Represents a site of chromosomal crossing-over - a form of genetic recombination.

chiasma (plural chiasmata)

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Complex of proteins that holds sister chromatids together along their length before their separation. (Figure 17–19)

cohesin - cohesin complex

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Complex of proteins involved in chromosome condensation prior to mitosis. Target for M-Cdk. (Figure 17–22)

condensin - condensin complex

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Ring containing actin and myosin that forms under the surface of animal cells undergoing cell division. Contracts to pinch the two daughter cells apart. (Figure 17–42)

contractile ring

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Protein that periodically rises and falls in concentration in step with the eukaryotic cell cycle. Cyclins activate crucial protein kinases (called cyclin-dependent protein kinases - or Cdks) and thereby help control progression from one stage of the cell cycle to the next.

cyclin

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Protein kinase that has to be complexed with a cyclin protein in order to act. Different cyclin–Cdk complexes trigger different steps in the cell-division cycle by phosphorylating specific target proteins. (Figure 17–10)

cyclin-dependent kinase (Cdk)

Protein complex formed periodically during the eukaryotic cell cycle as the level of a particular cyclin increases. A cyclin-dependent kinase (Cdk) then becomes partially activated. (Figures 17–10 and 17–11 - and Table 17–1 - p. 969)

cyclin–Cdk complex

see anaphase-promoting complex

cyclosome

Division of the cytoplasm of a plant or animal cell into two - as distinct from the associated division of its nucleus (which is mitosis). Part of M phase. (Panel 17–1 - pp. 980–981)

cytokinesis

Transcription regulatory protein that switches on many genes that encode proteins required for entry into the S phase of the cell cycle.

E2F protein

State of withdrawal from the eukaroytic cell-division cycle by entry into a quiescent digression from the G1 phase. A common - sometimes permanent - state for differentiated cells.

Gap 1 phase of the eukaryotic cell-division cycle - between the end of mitosis and the start of DNA synthesis. (Figure 17–4)

G1 phase

Cyclin–Cdk complex formed in vertebrate cells by a G1-cyclin and the corresponding cyclin-dependent kinase (Cdk). (Table 17–1 - p. 969)

G1-Cdk

Cyclin present in the G1 phase of the eukaryotic cell cycle. Forms complexes with Cdks that help govern the activity of the G1/S-cyclins - which control progression to S phase.

G1-cyclin

Cyclin–Cdk complex formed in vertebrate cells by a G1/S-cyclin and the corresponding cyclin-dependent kinase (Cdk). (Figure 17–11 and Table 17–1 - p. 969)

G1/S-Cdk

Cyclin that activates Cdks in late G1 of the eukaryotic cell cycle and thereby helps trigger progression through Start - resulting in a commitment to cell-cycle entry. Its level falls at the start of S phase. (Figure 17–11)

G1/S-cyclin

Gap 2 phase of the eukaryotic cell-division cycle - between the end of DNA synthesis and the beginning of mitosis. (Figure 17–4)

G2 phase

Point in the eukaryotic cell cycle at which the cell checks for completion of DNA replication before triggering the early mitotic events that lead to chromosome alignment on the spindle. (Figure 17–9)

G2/M transition

Protein that prevents the formation of new prereplicative complexes during S phase and mitosis - thus ensuring that the chromosomes are replicated only once in each cell cycle.

geminin

Extracellular signal protein that can stimulate a cell to grow. They often have other functions as well - including stimulating cells to survive or proliferate. Examples include epidermal growth factor (EGF) and platelet-derived growth factor (PDGF).

growth factor

Long period of the cell cycle between one mitosis and the next. Includes G1 phase - S phase - and G2 phase. (Figure 17–4)

interphase

In the mitotic or meiotic spindle - a microtubule interdigitating at the equator with the microtubules emanating from the other pole. (Figure 17–23)

interpolar microtubule

Large protein complex that connects the centromere of a chromosome to microtubules of the mitotic spindle. (FIgure 17–30)

kinetochore

In the mitotic or meiotic spindle - a microtubule that connects the spindle pole to the kinetochore of a chromosome.

kinetochore microtubule

Cyclin-Cdk complex formed in vertebrate cells by an M-cyclin and the corresponding cyclin-dependent kinase (Cdk). (Figure 17–11 and Table 17–1 - p. 969)

M-Cdk (M-phase Cdk)

A cyclin found in all eukaryotic cells that promotes the events of mitosis. (Figure 17–11)

M-cyclin

The first of two rounds of chromosome segregation following meiotic chromosome duplication; segregates the homologs - each composed of a tightly linked pair of sister chromatids.

meiosis I

The second of two rounds of chromosome segregation following meiotic chromosome duplication; segregates the sister chromatids of each homolog.

meiosis II

Imaginary plane at right angles to the mitotic spindle and midway between the spindle poles; the plane in which chromosomes are positioned at metaphase. (Panel 17–1 - pp. 980–981)

metaphase plate

Transition in the eukaryotic cell cycle preceding sister-chromatid separation at anaphase. If the cell is not ready to proceed to anaphase - the cell cycle is halted at this point. (Figure 17–9 - and Panel 17–1 - pp. 980–981)

metaphase-to-anaphase transition

Movement of individual tubulin molecules in the microtubules of the spindle toward the poles by loss of tubulin at their minus ends. Helps to generate the poleward movement of sister chromatids after they separate in anaphase. (Figure 17–35)

microtubule flux

Structure formed at the end of cleavage that can persist for some time as a tether between the two daughter cells in animals. (Figure 17–43)

midbody

Extracellular signal molecule that stimulates cells to proliferate.

mitogen

Bipolar array of microtubules and associated molecules that forms in a eukaryotic cell during mitosis and serves to move the duplicated chromosomes apart. (Figure 17–23 and Panel 17–1 - pp. 980–981)

mitotic spindle

Transcription regulatory protein that is activated when a cell is stimulated to grow and divide by extracellular signals. It activates the transcription of many genes - including those that stimulate cell growth. (Figure 17–61)

Myc

Event occurring occasionally during meiosis in which a pair of homologous chromosomes fails to separate so that the resulting germ cell has either too many or too few chromosomes.

nondisjunction

A gene regulatory protein that is activated by damage to DNA and is involved in blocking further progression through the cell cycle. Tumor suppressor gene that is mutated in about half of human cancers. Encodes a transcription regulator that is activated by damage to DNA and is involved in blocking further progression through the cell cycle. (Figures 20–27 - 20-37 - and 20–40)

p53

In meiosis - the lining up of the two homologous chromosomes along their length. (Figure 17–54)

pairing

Structure made of microtubules and actin filaments that forms in the prospective plane of division of a plant cell and guides formation of the cell plate. (Figure 17–49)

phragmoplast

Circumferential band of microtubules and actin filaments that forms around a plant cell under the plasma membrane prior to mitosis and cell division. (Figure 17–49)

preprophase band

Multiprotein complex that is assembled at origins of replication during late mitosis and early G1 phases of the cell cycle; a prerequisite to license the assembly of a preinitiation complex - and the subsequent initiation of DNA replication. (Figures 17–17 and 17–18)

prereplicative complex (preRC)

Phenomenon observed in primary cell cultures in which cell proliferation slows down and finally irreversibly halts.

replicative cell senescence

Important transition at the end of G1 in the eukaryotic cell cycle; commits the cell to enter S phase. The term was originally used for this transition in the mammalian cell cycle; in this book we use the term Start. (Figure 17–9)

restriction point

Tumor suppressor protein involved in the regulation of cell division. Mutated in the cancer retinoblastoma - as well as in many other tumors. Its normal activity is to regulate the eukaryotic cell cycle by binding to and inhibiting the E2F proteins - thus blocking progression to DNA replication and cell division. (Figure 17–61)

retinoblastoma protein (Rb)

Cyclin–Cdk complex formed in vertebrate cells by an S-cyclin and the corresponding cyclin-dependent kinase (Cdk). (Figure 17–11 and Table 17–1 - p. 969)

S-Cdk

Member of a class of cyclins that accumulate during late G1 phase and bind Cdks soon after progression through Start; they help stimulate DNA replication and chromosome duplication. Levels remain high until late mitosis - after which these cyclins are destroyed. (Figure 17–11)

S-cyclin

Family of ubiquitin ligases formed as a complex of several different proteins. One is involved in regulating the eukaryotic cell cycle - directing the destruction of inhibitors of S-Cdks in late G1 and thus promoting the activation of S-Cdks and DNA replication. (Figures 3–71 and 17–15)

SCF

Protein that binds to the protease separase and thereby prevents its cleavage of the protein linkages that hold sister chromatids together in early mitosis. Securin is destroyed at the metaphase-to-anaphase transition. (Figure 17–38)

securin

Protease that cleaves the cohesin protein linkages that hold sister chromatids together. Acts at anaphase - enabling chromatid separation and segregation. (Figure 17–38)

separase

Tightly linked pair of chromosomes that arise from chromosome duplication during S phase. They separate during M phase and segregate into different daughter cells. (Figure 17–21)

sister chromatids

Regulatory system that operates during mitosis to ensure that all chromosomes are properly attached to the spindle before sister-chromatid separation starts. (Figure 17–9 and Panel 17–1 - pp. 980–981)

spindle assembly checkpoint

Important transition at the end of G1 in the eukaryotic cell cycle. Passage through Start commits the cell to enter S phase. The term was originally used for this point in the yeast cell cycle only; the equivalent point in the mammalian cell cycle was called the restriction point. In this book we use Start for both. (Figure 17–9)

Start (restriction point)

Structure that holds paired homologous chromosomes tightly together in pachytene of prophase I in meiosis and promotes the final steps of crossing-over. (Figures 17–55 and 17–56)

synaptonemal complex

Mass of cytoplasm containing many nuclei enclosed by a single plasma membrane. Typically the result either of cell fusion or of a series of incomplete division cycles in which the nuclei divide but the cell does not.

syncytium

Final stage of mitosis in which the two sets of separated chromosomes decondense and become enclosed by nuclear envelopes. (Panel 17–1 - pp. 980–981)

telophase

Protein kinase that inhibits Cdk activity by phosphorylating amino acids in the Cdk active site. Important in regulating entry into M phase of the cell cycle.

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