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The eukaryotic cell cycle consists of several distinct phases: what happens in interphase?
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Cell Biology Ch. 18
Cell-Division Cycle
| Question | Answer |
|---|---|
| cell cycle | the orderly sequence of events by which a cell duplicates its contents and divides into two |
| The eukaryotic cell cycle consists of several distinct phases: what happens in interphase? | the cell grows and the nuclear DNA is replicated |
| The eukaryotic cell cycle consists of several distinct phases: what happens in M phase? | the nucleus divides (mitosis) followed by the cytoplasm (cytokinesis) |
| Interphase encompasses three phases of the cell cycle: | S phase, G1 phase, and G2 phase |
| Interphase: What happens during the S phase? | cell replicates its DNA |
| Interphase: S phase is flanked by two "gap" phases- called G1 and G2. What happens during these phases? | the cell continues to grow a prepare for S phase and M phase by monitoring both internal state and external environment |
| Interphase: At particular point in G1 and G2, the cell decides what? | whether to proceed to the next phase or pause to allow more time to prepare |
| During all of interphase, a cell generally continues to what? (3) | transcribe genes, synthesize proteins, and grow in mass |
| If interphase lasted only long enough for DNA replication, what would happen to the cell? | it would not have time to double its mass before it divided and would consequently shrink with each division |
| to ensure that they replicate all their DNA and organelles, and divide in an orderly manner, eukaryotic cells possess a complex network of regulatory proteins known as the _______-________ _________ ____________ | cell-cycle control system |
| cell-cycle control system | network of regulatory proteins that govern the orderly progression of a eukaryotic cell through the stage of cell division |
| The cell-cycle control system regulates progression through the cell cycle at three main transition points: | G1 to S phase, G2 to M phase, and during mitosis |
| The cell-cycle control system regulates progression through the cycle at three main transition points: what does the control system check for at the transition of G1 to S phase? | confirms that the environment is favorable to proliferation before committing to DNA replication |
| The cell-cycle control system regulates progression through the cycle at three main transition points: If extracellular conditions are unfavorable, cells can delay progress through G1 and may even enter a specialized resting state known as what? | G0 |
| The cell-cycle control system regulates progression through the cycle at three main transition points: what does the control system check for at the transition of G2 to M phase? | confirms that the DNA is undamaged and fully replicated, ensuring that the cell does not enter mitosis unless its DNA is intact |
| The cell-cycle control system regulates progression through the cycle at three main transition points: what does the control system check for during mitosis? | ensures that the duplicated chromosomes are properly attached to the mitotic spindle before the spindle pulls the chromosomes apart and segregates them into the two daughter cells |
| the cell-cycle control system coordinates events of the cell cycle by sequentially and cyclically switching on and off what? | key proteins and protein complexes |
| the cell-cycle control system depends on what type of protein kinases? | cyclin-dependent protein kinases (Cdpks) |
| How are cyclin-depend protein kinases (Cdks) activated? | cyclically activated by the bind of cyclin proteins and by phosphorylation and dephosphorylation |
| cyclin proteins | regulatory protein whose concentration rises and falls at specific times during the eukaryotic cell cycle. they help control progression from one stage to the bext by binding to cyclin-dependent protein kinases (Cdks) |
| different types of cyclin-Cdk complexes trigger different steps in the cell cycle: The cyclin that acts in G2 to trigger entry into M phase is called ___ cyclin, and the active complex it forms with its Cdk is called ___-Cdk | M |
| different types of cyclin-Cdk complexes trigger different steps in the cell cycle: cyclins, called ___ cyclins and __/__ cyclins, bind to a distinct Cdk protein late in G1 to form __-Cdk and __/__-Cdk, respectively. These complexes help launch S phase | S cyclins, G1/S-cyclins, S-Cdk and G1/S-Cdk |
| different types of cyclin-Cdk complexes trigger different steps in the cell cycle: Cyclins, called ___ cyclins, act earlier in G1 and bind to other Cdk proteins to form ___-Cdks, which help drive the cell through G1 toward S phase | G1, G1-Cdks |
| Each of these cyclin-Cdk complexes do what? | phosphorylates a different set of target proteins in the cell |
| cyclin concentrations are regulated by what? | transcription (rate protein is synthesized) and proteolysis (rate protein is degraded) |
| the abrupt degradation of M and S cyclins part way through M phase depends on what large enzyme complex? | anaphase-promoting complex (APC) |
| What does the anaphase-promoting complex (APC) do? | tags cyclins with a chain of ubiquitin, marking them for rapid degradation, returning Cdk to an inactive state |
| the activity of cyclin-Cdk complexes depends on phosphorylation and dephosphorylation. Explain | cyclin-Cdk contain inhibitory phosphates, and to become active, the Cdk must be dephosphorylated by a specific protein phosphatase |
| In addition to phosphorylation and dephosphorylation, the activity of Cdks can also be modulated by the bind of what? | Cdk inhibitor proteins |
| Cdk inhibitor proteins | regulatory proteins tha tblocks the assembly or activity of cyclin-Cdk complexes, delaying progression primarily through G1 and S phase of the cell cycle |
| the cell-cycle control system can halt the cycle at specific transition points to ensure that intracellular and extracellular conditions are favorable and that each step is complete before the next is started. Some rely on Cdk inhibitors which do what? | block the activity of one or more cyclin-Cdk complexes |
| G1 phase: bustling period of metabolic activity, cell growth, and repair, but it is also important point of ____________-____________ for the cell | decision-making |
| G1 phase: After M phase, when cells are actively dividing, the cell-cycle control system must be inactivated and "reset to generate a more stable G1 phase, during which the cell can grow and monitor its environment before committing to a new round? (2) | the cell-cycle control machinery inactivates S-Cdk and M-Cdk by blocking the synthesis of new cyclins by and deploying Cdk inhibitor proteins to muffle any activity of the remaining cyclin-Cdk |
| G1 phase: an extracellular signal molecule, called a __________ , promote the production of cyclins that stimulate cell division | mitogen |
| G1 phase: mitogen | extracellular signal molecule that stimulates cell proliferation |
| G1 phase: What happens to a cell deprived of mitogens for long enough? | cell cycle arrests. the cell will withdraw from the cell cycle and enter a nonproliferating state |
| G1 phase: Escape from nonproliferating states requires the accumulation of __________ | cyclins |
| G1 phase: How do mitogens act? | switch on cell signaling pathways that stimulate the synthesis of G1 cyclins, G1/S cyclins, and other proteins involved in DNA synthesis and chromosome duplication |
| G1 phase: What does the build up of G1 cyclins and G1/S cyclins (caused by mitogens) trigger? | triggers a wave of G1/S-Cdk activity, which ultimately relieves the negative controls that otherwise block progession from G1 to S phase |
| G1 phase: what can temporarily halt progression through G1? | DNA damage |
| G1 phase: What does the DNA damage in G1 causes? | increase in both the concentration and activity of a protein called p53 |
| G1 phase: p53 | transcription regulator that controls the cells response to DNA damage, preventing the cell from entering S phase until the damage has been repaired or inducing the cell to commit suicide if the damage is too extensive. |
| G1 phase: p53 is a transcription regulator that activates the transcription of a gene encoding a Cdk ___________, called p21 | inhibitor |
| G1 phase: how does the Cdk inhibitor, p21, do in response to increases p53 levels, which was triggered by DNA damage? | it binds to g1/S phase and S-Cdk, preventing them from driving the cell to S phase |
| G1 phase: if the DNA damage is too severe to be repaired, p53 can induce the cell to kill itself by undergoing a form of programmed cell death called ______________ | apoptosis |
| G1 phase: What is the consequence if a cell replicated damaged DNA before repairing it? | high rate of mutation and the production of cells that tend to become cancerous |
| G1 phase: Many cells in the body permanently stop dividing when they differentiate. What are these cells called? | terminally differentiated cells |
| G1 phase: What are some examples of terminally differentiated cells? | nerve or muscle cells |
| G0 phase: in the absence of appropriate signals, other cell types withdraw from the cell cycle only temporarily, entering an _________ state called G0 | arrested |
| G0 phase: What is the difference between terminally differentiated cells and cells that enter G0? | cells that enter G0 retain the ability to reassemble the cell-cycle control system quickly and to divide again. |
| S phase: before a cell divides, it must ___________ its DNA | replicate |
| S phase: for eukaryotic cells, preparation for replication begins early in ___ phase, by the recruitment of proteins to the sites along each chromosome where replication will begin | G1 |
| S phase: The nucleotide sequences, called _____________ of ___________, serve as landing pads for the proteins and protein complexes that control and carry out DNA synthesis | origins of replication |
| S phase: One of these complexes, called the _______ ___________ ____________, remains perched atop the replication origins throughout the cell cycle, where it recruits a protein called Cdc6 | origin recognition complex (ORC) |
| S phase: together, ORC and protein Cdc6 do what? | load the DNA helicase that will open up the double helix and ready the origin of replication |
| S phase: What actually initiates DNA replication while also blocking re-replication? | S-cdk |
| S phase: When is S-Cdk assembled and activated? | at the end of G1 |
| S phase: during S phase, what does S-Cdk do to initiate DNA replication? | activates DNA helicases in the prereplicative complex and promotes the assembly of the rest of the proteins that form the replication fork. This initiates DNA replication |
| S phase: How does S-Cdk prevent rereplication? | if helps phosphorylate Cdc6, which marks that protein for degradation |
| S phase: What happens if errors occur during DNA replication or if replication is delayed? | the cell-cycle control system can delay entry into M phase |
| S phase: the activity of M-Cdk is inhibited by phosphorylation at particular sites. For the cell to progress into mitosis, these inhibitory phosphatases must be removed, how? | by activating protein phosphatase, called Cdc25 |
| S phase: When DNA is damaged or incompletelt replicated, Cdc25 is itself inhibited, preventing the removal of inhibitory phosphatases. What results? | M-Cdk remains inactive and M phase is delayed until DNA replication is complete and any DNA damage is repaired |
| Once a cell has successfully replicated its DNA in S phase, and progressed through G2, it is ready to enter ___ phase, where the cell is divided into two identical daughter cells | M phase |
| M phase: During this period, the cell will do what two things? | divide its nucleus (mitosis) and then its cytoplasm (cytokinesis) |
| M phase: ___-_____ helps prepare the duplicated chromosomes for segregation and induces the assembly of the mitotic spindle | M-Cdk |
| M phase: mitotic spindle | machinery that will pull the duplicated chromosomes apart |
| M phase: M-Cdk complexes accumulate throughout ____, but this stockpile is not activated until the end of ____ | G2 |
| M phase: How are the M-Cdk activated at the end of G2? | activating phosphatase Cdc25 removes inhibitory phosphates holding M-Cdk activity in check |
| M phase: M-Cdk activation is self-reinforcing. Explain | once activated, it phosphorylates, and thereby activate more Cdk-activating phosphatase(Cdc25). This phosphatase can now activate more M-Cdk by removing inhibitory phosphate groups from the Cdk subunit |
| M phase: When the cell enters M phase, duplicated chromosomes condense. Protein complexes called __________ help carry out this chromosome condensation | condensins |
| M phase: condensins | protein complex that helps configure duplicated chromosomes for segregation by making them more compact |
| M phase: The assembly of condensin complexes onto the DNA is triggered by what? | the phosphorylation of condensins by M-Cdk |
| M phase: immediately after a chromosome is duplicated during S phase, the two copies remain tightly bound together. These identical copies are called ___________ _____________, each containing a single, double-stranded molecule of DNA,/associated proteins | sister chromatids |
| M phase: The sister chromatids are held together by protein complexes called __________, which assemble along the length of each chromatid as the DNA is replicated | cohesins |
| M phase: Different cytoskeletal assemblies carry out mitosis and cytokinesis. What carries out nuclear division (mitosis) | the mitotic spindle |
| M phase: Different cytoskeletal assemblies carry out mitosis and cytokinesis. What carries out cytoplasmic division (cytokinesis) | the contractile ring |
| M phase: Although M phase proceeds as a continuous sequence of events, it is divided into a series of stages. What are the first five stages of M phase, that constitute mitosis? | prophase, prometaphase, metaphase, anaphase, and telophase |
| M phase: Although M phase proceeds as a continuous sequence of events, it is divided into a series of stages. What is the last stage of M phase? beginning before mitosis ends | cytokinesis |
| M phase: Before M phase begins, what two critical events must be completed? | DNA must be fully replicated and the centrosome must be duplicated |
| M phase: centrosome | microtubule-organizing center that sits near the nucleus. During cell cycle, this structure duplicates to form the two poles of the mitotic spindle |
| M phase: As mitosis begins, the two centrosomes separate, and each nucleates a radial array of microtubules called an _______ | aster |
| M phase: What do the asters do? | move to opposite sides of the nucleus for form the two poles of the mitotic spindle |
| M phase: the process of centrosome duplication and separation is known as what? | the centrosome cycle |
| M phase: centrosome cycle | process by which the centrosome duplicates (during interphase) and the two new centrosomes separate (at the beginning of mitosis) to form the poles of the mitotic spindle |
| Mitosis: What two things occur during prophase? | the duplicated chromosomes condense. outside the nucleus, the mitotic spindle assembles between the two centrosomes which have begun to move apart |
| Mitosis: mitotic spindle | array of microtubules and associated molecules that forms between the opposite poles of a cell during mitosis and pulls duplicated chromosome sets apart |
| Mitosis: spindle pole | centrosome from which microtubules radiate to form the mitotic spindle |
| Mitosis: Prometaphase starts abruptly with what? | the breakdown of the nuclear envelope |
| Mitosis: Prometaphase starts abruptly with the breakdown of the nuclear envelope. What else happens in prometaphase? | chromosomes can now attach to spindle microtubules via their kinetochores and udergo active movement |
| Mitosis: kinetochore | protein complex that assembles on the centromere of a condensed mitotic chromosome, the site to which spindle microtubules attach |
| Mitosis: chromosomes are more than passive passengers in the process of spindle assembly. What do they do? | stabilize and organize microtubules into functional mitotic spindles |
| Mitosis: At metaphase, how are the chromosomes oriented? | they are aligned at the equator of the spindle, midway between the spindle poles (forming the metaphase plate) |
| Mitosis: What else happens during metaphase? | the kinetochore microtubules on each sister chromatid attach to opposite poles of the spindle |
| Mitosis: What is the main event in anaphase? | sister chromatids synchronously separate and are pulled slowly toward the spindle pole to which they are attached. |
| Mitosis: How are sister chromatids separated at the beginning of anaphase? | the cohesin linkages that hold sister chromatids together are broken by a protease called separase |
| Mitosis: before anaphase, separase is held in an inactive state by an inhibitory protein called __________ | securin |
| Mitosis: at the beginning of anaphase, securin is targeted for destruction by _____- the same protein complex that marks M cyclin for degradation | APC |
| Mitosis: the movement of chromosome segregation is a consequence of two independent processes that depend on different parts of the mitotic spindle. Anaphase A | kinetochore microtubules shorten and the attached chromosomes move poleward |
| Mitosis: the movement of chromosome segregation is a consequence of two independent processes that depend on different parts of the mitotic spindle. Anaphase B | the spindle poles themselves move apart further segregating the two sets of chromosomes |
| Mitosis: What is the driving force for the movements of anaphase A? | provided by the loss of tubulin subunits from both ends of the kinetochore microtubules |
| Mitosis: What is the driving force for the movements of anaphase B? | two sets of motor proteins, kinesin and dynein families, operating on different types of spindle microtubules |
| Mitosis: kinesin proteins act on what type of microtubule? | long, overlapping, sliding the microtubules from opposite poles past one another at the equator of the spindle, pushing the spindle poles apart |
| Mitosis: Dynein proteins do what? | anchored to the cell cortex, pull the poles apart |
| Mitosis: Telophase marks the end of mitosis. What occurs during telophase? | two sets of chromosomes arrive at the poles of the spindle. New nuclear envelope reassembles around each set, completing the formation of two nuclei |
| Mitosis: near the end of telophase, the division of the cytoplasm begins with the assembly of the _________________ _________ | contractile ring |
| cytokinesis | process by which the cytoplasm is cleaved in two |
| cytokinesis: the cytoplasm is divided in two by a contractile ring of _________ and _________ filaments, which pinches the cell into two daughters, each with one nucleus | actin and myosin |
| cytokinesis: in plant cells, a new ______ _____ forms inside the parent cell to divide the cytoplasm in two | cell wall |
| in animal cells, extracellular signals regulate cell numbers by controlling what three things? | cell survival, cell growth , and cell proliferation |
| Most animal cells require survival signals from other cells to avoid _____________, a form of cell suicide mediated by a proteolytic caspase cascade | apoptosis (regulated by Bc12 family) |
| animal cells proliferate if stimulated by what? | extracellular mitogens produced by other cells (mitogens release normal intracellular brakes that block progression from G1 or G0 into S phase) |
| for an organism or organ to grow, cells must grow as well as divide. Animal cell growth depends on what? | extracellular growth factors that stimulate protein synthesis and inhibit protein degradation |
| cancer cells fail to obey normal "social" controls on cell behavior, resulting in what? | the cancer cells outgrow, out-divide, and out-survive their normal neighbors |
| survival factors | promote cell survival |
| mitogens | stimulate cell division |
| growth factors | stimulate cell growth |
Created by:
cmccartney2