Term
| The orderly sequence of events by which a cell duplicates its contents and divides in two is.... |
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Definition
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Term
| What is the cell cycle control system? |
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Definition
| A complex network of regulatory proteins the core of which is a series of biochemical switches that control the main events including DNA replication and segregation of duplicated chromosomes |
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Term
| What are the phases of the cell cycle? |
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Definition
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Term
| What is the period between each M phase called? |
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Definition
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Term
| What marks the end of the G2 phase? |
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Definition
| The chromosomes condensing |
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Term
| Following replication, the two copies of each chromosome are (loosely/tightly) bound together |
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Definition
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Term
| Describe the "checkpoint" at G1 |
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Definition
| Cells confirm that the environment is favorable for cell proliferation and its DNA is intact before committing to S phase |
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Term
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Definition
| A specialized resting state in which a cell doesn't move from G1 to S because of unfavorable extracellular conditions |
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Term
| Describe the "checkpoint" at G2 |
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Definition
| Cells ensure that they do not enter Mitosis until damaged DNA is repaired and DNA replication is complete |
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Term
| How does the cell-cycle control system govern the cell-cycle machinery? |
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Definition
| By cyclically activating and then inactivating the key proteins and protein complexes that initiate or regulate DNA replication, mitosis, and cytokinesis |
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Term
| What are protein kinases? |
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Definition
| A set of enzymes that transfer a phosphate group from ATP to a particular amino acid side chain on the target protein. |
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Term
| What are protein phosphatases? |
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Definition
| A set of enzymes that remove the phosphate group from a target protein (dephosphorylation) in order to inactivate the protein |
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Term
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Definition
| A set of protein components of the control system. No enzymatic activity of their own, but bind to cell-cycle kinases before they kinases can become enzymatically active. The kinases of the cell-cycle are therefore known as cyclin-dependent protein kinases. Cdks |
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Term
| Why are cyclins called cyclins? |
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Definition
| Because, unline the cyclin-dependent kinases, their concentrations vary in a cyclical fashion during the cell cycle |
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Term
| What does a Cdk achieve by using cyclin? |
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Definition
| A Cdk uses cyclin to become enymatically active, also the cyclin helps direct the Cdk to its target proteins |
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Term
| The cyclin that helps drive cells into M phase is called ________ and the active complex it forms with its Cdk is called ______ |
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Definition
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Term
| Synthesis of M-Cyclin starts when? How does the synthesis progress and when does it end? |
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Definition
| Begins immediately after cell division and continues steadily throughout interphase. The accumulation of cyclin helps time the onset of mitosis; its rapid elimination then helps initiate the exit from mitosis |
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Term
| What controls when cyclins are ubiquinated and thus tagged for elimination? |
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Definition
| In the case of M-cyclin, it's a protein complex called APC (Anaphase Promoting Complex) which adds ubiquiting to the cyclin and other proteins. |
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Term
| How does M-Cdk contribute to its own eventual inactivation? |
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Definition
| Activation of M-Cdk starts a process with built-in delay which activates APC, and then APC ubiquinates and degrades the M-cyclin, thereby inactivating the M-Cdk |
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Term
| M-cyclin increases gradually throughout interphase but M-Cdk activity switches on rapidly at the end of interphase. What triggers this rapid activation of M-Cdk? |
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Definition
| M-Cdk is maximally active only when phosphorylated at certain sites by a specific protein phosphatase, and dephosphorylated by a protein phosphatase. The activated complex can activate more of the same; the positive feedback produces the explosion of M-Cdk activity that drives the cell into M-phase |
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Term
| How does M-Cdk cause events that herald the entry into mitosis? |
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Definition
| M-Cdk phosphorylates key proteins causing chromosomes to condense, nuclear envelope to break down, and microtubules of the cytoskeleton to form the mitotic spindle |
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Term
| What is the purpose of S-Cdk? |
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Definition
| It initiates DNA replication and helps block re-replication. |
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Term
| What is the origin recognition complex (ORC) |
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Definition
| It is the multi-protein complex attached to the origins of replication on DNA, serves as a landing pad for other regulatory S-phase proteins, like Cdc6 |
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Term
| What is Cdc6 and how does it relate to the pre-replicative complex? What breaks Cdc6 down? Why does this happen? |
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Definition
| Cdc6 is a regulatory protein which binds to the Origin Recognition Complex in G1, forming the pre-replicative complex. Activation of S-Cdk late in G1 "fires" the origin, it then phosphorylate Cdc6, which removes it from the ORC and marks it for ubiquitination and degradation to prevent rereplication of DNA |
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Term
| What happens to the Cdk activity at the end of mitosis? |
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Definition
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Term
| What are Cdk inhibitor proteins? |
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Definition
| Cdk inhibitor proteins block the assembly or activity of one or more cyclin-Cdk complexes, to stop the cell cycle progression at a certain checkpoint |
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Term
| What is p53? What does it do, and what happens when the p53 gene is mutated? |
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Definition
| p53 is a gene regulatory protein which is amplified by damaged DNA. The p53 gene then can activate the transcription of another gene encoding a Cdk inhibitor protein called p21. p21 binds to G1/S-Cdk and S-Cdk, preventing them from driving the cell into S phase. Missing or defective p53 causes unrestrained replication of damaged DNA, which produces cancerous cells. |
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Term
| What is the most radical decision the cell-cycle control system can make? |
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Definition
| To withdraw from the cell cycle entirely and stop the cell from dividing. |
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Term
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Definition
| a modified G1 state in which the cell-cycle control system is largely dismantled, in that many of the Cdks and cyclins disappear. |
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Term
| Why is the G1 phase sometimes called "Start"? |
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Definition
| Because passing G1 represents a commitment to complete a full division cycle. |
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Term
| What are the cell-cycle checkpoints during G1 phase? |
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Definition
| Unfavorable extracellular environment? Damaged DNA? (p53) |
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Term
| What are the cell-cycle checkpoints during S phase? |
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Definition
| Is the DNA completely replicated? |
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Term
| What are the cell-cycle checkpoints during G2 phase? |
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Definition
| Is the DNA damaged or incompletely replicated? |
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Term
| What are the cell-cycle checkpoints during M phase? |
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Definition
| Is every chromosome properly attached to the mitotic spindle? |
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Term
| What is the Greek word for programmed cell death? |
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Definition
| Apoptosis ("falling off" as leaves fall from a tree) |
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Term
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Definition
| When a cell dies by acute injury, they swell and burst, spilling their contents |
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Term
| What makes apoptosis so neat? |
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Definition
| The cytoskeleton collapses, the nuclear envelope disassembles, and the nuclear DNA breaks into fragments. The cell surface attracts phagocytic cells to clean it up |
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Term
| Apoptosis is carried out by a family of _________, enzymes that cut up other proteins, called _________ |
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Definition
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Term
| How do caspases become activated from _______ (the inactive form) and then what do they do? |
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Definition
| Procaspases are activated by proteolytic cleavage. They cleave, thereby activating, other members of the family, resulting in an amplifying proteolytic cascade. They cleave other key proteins like the lamins of the nuclear envelope |
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Term
| What are sister chromatids? |
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Definition
| When the chromosomes are duplicated in S phase, the two copies of each replicated chromosome are tightly bound together |
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Term
| What proteins hold together the sister chromatids? |
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Definition
| Protein complexes called cohesins |
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Term
| What proteins help carry out the condensation of the chromosomes? |
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Definition
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Term
| How do the chromosomes condense at the start of M phase? |
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Definition
| M-Cdk triggers the assembly of condensin protein complexes onto DNA by phosphorylating the condensin subunits. Condensins help the DNA condense |
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Term
| What cytoskeletal structure is responsible for cytokinesis? |
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Definition
| The contractile ring, consists of actin and myosin filaments arranged in a ring on the equator of the cell. The ring contracts and pulls the membrane inward, dividing the cell in two |
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Term
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Definition
| the principal microtubule-organizing center in animal cells |
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Term
| How does the centrosome relate to the mitotic spindle? |
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Definition
| It is duplicated at the start of S phase, and the two centrosomes are the poles for the mitotic spindle. |
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Term
| What are the first 5 stages of M phase? What is the last? |
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Definition
Prophase, Prometaphase, Metaphase, Anaphase, Telophase
Cytokinesis |
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Term
| When does cytokinesis start and end? |
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Definition
| Starts in anaphase and ends after telophase |
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Term
| What happens during Prophase? |
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Definition
| The replicated chromosomes condense and the mitotic spindle begins to form around the nucleus. |
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Term
| What happens during Prometaphase? |
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Definition
| The nuclear envelope breaks down, allowing the spindle microtubules to contact the chromosomes and bind to them at their kinetochore and initiate active movement |
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Term
| What happens during Metaphase? |
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Definition
| The mitotic spindle gathers all of the chromosomes to the center (equator) of the spindle. |
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Term
| What happens during Anaphase? |
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Definition
| The two sister chromatids split apart, and the spindle draws them to opposite poles of the cell. |
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Term
| What happens during Telophase? |
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Definition
| A nuclear envelope reassembles around each of the two sets of separated chromosomes to form two nuclei. |
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Term
| When is there a marked increase in the dynamic instability of the microtubules? |
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Definition
| At the start of mitosis, when the microtubules forming the cytoplasmic array disassemble and start to reassemble into the mitotic spindle. |
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Term
| When do the two "daughter" centrosomes separate? |
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Definition
| At the beginning of Prophase, they are the poles which form the mitotic spindle. |
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Term
| What phase of mitosis begins abruptly with the disassembly of the nuclear envelope? |
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Definition
| Prometaphase. This frees the chromosomes. |
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Term
| Where do the spindle microtubules attach to the chromosomes? |
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Definition
| The kinetochores, which assemble on the condensed chromosomes during late Prophase. They assemble at the centromeres, which are the regions of constriction on the DNA, thus pointing the sister chromatids to opposite sides of the cell. |
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Term
| How does Anaphase abruptly begin? |
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Definition
| The cohesin linkage between sister chromatids is released, allowing the now called "daughter chromosomes" to segregate to opposite ends of the spindle. |
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Term
| What triggers the abrupt disruption of the cohesin linkage between sister chromatids? |
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Definition
| The activation of the Anaphase Promoting Complex, which cleaves an inhibitory protein, thereby releasing a proteolytic enzyme that breaks the cohesin linkage. |
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Term
| What happens in Anaphase A? |
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Definition
| The kinetochore microtubules shorten by depolymerization, the attached chromosomes move poleward. |
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Term
| What happens in Anaphase B? |
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Definition
| The spindle poles themselves move apart, further contributing to the segregation of the two sets of daughter chromosomes. |
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Term
| How do organelles such as mitochondria and chloroplasts move into daughter cells? |
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Definition
| Often they will fragment and hitch a ride on the spindle microtubules via motor proteins |
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Term
| What is the angle between the mitotic spindle and the plane of cytoplasmic cleavage during Cytokinesis? |
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Definition
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Term
| How does "cytokinesis" occur in plant cells? |
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Definition
| cell divison occurs by the formation of a new cell wall inside the cell, which divides the cytoplasm in two. |
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Term
| What types of cells enter G0? |
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Definition
| Somatic cells, this stage can be permanent (neurons). |
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