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120 Cards in this Set
- Front
- Back
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what is cell communication necessary for
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structural and functional integrity of tissues and organs
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what necessitated cellular specialization and cellular signaling
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the evolution of multicellular organisms
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what do communication mechanisms depend on
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extracellular signal molecules and a mechanism for cells to respond to these signals
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what is signal transduction
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the process by which a cell converts an extracellular signal into a response
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what are the different ways in which a cell communicates?
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-contact dependent
-paracrine -synaptic -endocrine |
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what are hormones
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an information carrying molecule that is secreted from a cell. circulates in the body, and acts on target cells far from the signaling cell
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can most hormones pass the plasma membrane? which can
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no, only steroid hormones
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what is the overview of cell signaling?
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reception->transduction->response
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what is transduction
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cascades of molecular interactions relay signals from receptors to target molecules in the cell
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what are the molecules that relay a signal from a receptor to response
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mostly proteins
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what are the benefits of the multistep pathway
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-can amplify a signal
-provide more opportunities for coordination and regulation |
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what does signal transduction usually involve
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conformational changes in relay molecules. these conformational changes can result from phosphorylation
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what is phosphorylation of proteins
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a major mechanism for regulating the activity of proteins, moving from an inactive to an active site
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what is a ligand
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a signal molecule; it fits into the receptor in a way thats similar to the interaction between a substrate an the catalytic site of an enzyme
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what does ligand binding usually cause
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a conformational change in the receptor protein, which is often the initial transduction of the signal
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what are the 3 main types of membrane receptors
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-G-protein linked receptors
-receptor tyrosine kinases -ion channel receptors |
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what is a G-protein couple receptor
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a plasma membrane receptor that works with the help of a G-protein
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how does the G-protein act as an on/off switch
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G proteins are activated when they bind GTP and are deactivated when they hydrolyze the bound GTP to GDP
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what are second messengers
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small, nonprotein, water-soluble molecules or ions that can readily spread throughout cells by diffusion
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what are often mediated by tyrosine-kinase receptors
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growth factors and local regulators that stimulate cells to grow and reproduce
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what is a distinguishing feature of the tyrosine-kinase receptor
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it can activate many signal transduction pathways simultaneously
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what are ion-channel receptors
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ligand gated ion channels-when a signal molecule binds as a ligand to the receptor, the gate allows specific ions through a channel in the receptor
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what did Sutherland characterize the mechanisms for cell signaling as
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in response to stress, the adrenal glands release into the bloodstream a hormone called adrenaline (epinephrine) which triggers "fight of flight response"
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what did sutherland show about epinephrine
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that epinephrine somehow activates a cytosolic enzyme called glycogen phosphorylase, which converts glycogen to glucose
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what did the experiment showing that activation of glycogen phosphorylase required intact cells suggest that
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-epinephrine doesn't activate glycogen phosphorylates directly
-the plasma membrane is somehow involved |
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what are the most common second messengers
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cyclic AMP (cAMP) and Ca++
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how is cAMP formed
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adenylyl cyclase, an enzyme in the plasma membrane, converts ATP to cAMP in response to extracellular signaling
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what quenches the extracellular signal
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when phosphodiesters convert cAMP to AMP
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what do kinase do
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add phosphate from ATP to the target molecule
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what is IP3
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a second messenger; when its cleaved, it diffuses through the cell and releases calcium by opening the gate
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what are relay molecules
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molecules that relay the signal from the receptor to the response
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what is the signal in many pathways transmitted by
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a cascade of protein phosphorylations
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what do phosphatase enzymes do
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remove the phosphates, quenching the signal
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where may the cell's response to an extracellular signal occur
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-cytoplasm
-nucleus |
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in response to cell signaling, the cell could:
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-survive
-divide -differentiate -die |
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what is apoptosis
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programmed cell suicide
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what does apoptosis prevent
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enzymes from leaking out of a dying cell and damaging neighboring cells
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what is apoptosis important in
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shaping an organism during embryonic decelopment
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what are caspases
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the main proteases (enzymes that cut up proteins) that carry out apoptosis
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what can apoptosis be triggered by
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-an extracellular death-signaling ligand
-DNA damage in the nucleus -protein misfolding in the nucleus |
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what diseases may apoptosis be involved in
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parkinsons, alzheimers
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what is cell division
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a process in which cells make 2 daughter cells that are genetically identical to the parental cell
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what does cell division require
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replication on genomic DNA, and then seperation of the 2 copies of genomic DNA into daughter cells
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what is the function of cell division
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-reproduction
-growth & development -tissue removal |
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what 2 processes must alternate to allow a cell to divide properly
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-doubling the genome
-separating the duplicated genome into 2 identical halves |
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what is the BIG PROBLEM in cell division?
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to accurately replicate then separate chromosomes so each daughter receives an identical set
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what is the origin of replication
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the discrete site where DNA replication begins
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why is cell division in bacteria simple
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they divide via binary fusion
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why is cell division in eukaryotes more problematic?
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-eukaryotes have more than 1 chromosome
-eukaryotes have much more DNA space |
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how do eukaryotes separate chromosomes (mitosis)
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-duplication of each chromosome during the S phase of the cell cycle produces a chromosome consisting of 2 identical sister chromatids that are attached
-condense the chromosomes into a compact form -separate the sister chromatids -distribute these exact replicas equally between the 2 daughter cells |
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What are the phases in which the cell cycle consists
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-G1 (cell growth)
-S (synthesis of DNA) -G2 (growth) -M (mitosis & cytokinesis) |
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what is interphase
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G1,S,G2- the part of the cell cycle when cells are not dividing and accounts for about 90% of the cycle
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what is mitosis
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the process by which cells divide their genetic material & nucleus
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how many chromosomes do human somatic cells have
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46
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how many chromosomes do human gametes have
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23
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what are chromosomes
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a combination of DNA & proteins
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what is chromatin
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a DNA-protein complex; its organized and packaged by associated proteins that maintain chromosomal structure and control gene activity
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what are histones
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basic proteins, acidic DNA coils around histone core, resembles beads on a string
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what is nucleosome
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DNA wrapped around a core of 8 histone proteins
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how does chromatin prepare for mitosis
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chromatin is further compacted by radial looping around a protein scaffold
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what is the structure of mitotic chromosomes
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-sister chromatids=2 copies of replicated chromosome
-centromere=constriction in chromosome -kinetochore=protein "disc" that will bind mitotic spindle -cohesion=complex of proteins holding replicated chromosomes 2gether, at their centromeres, until theyre properly configured for seperation |
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what are the 5 sub-phases that mitosis is broken into
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-prophase
-pro-metaphase -metaphase -anaphase -telophase |
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what happens just before mitosis begins
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-In S phase, chromosomes have been duplicated.
-seeds of mitotic spindle (centrioles) begin to grow |
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what is the centrosome
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a microtubule organizing center that nucleates the formation of the mitotic spindle
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what is the mitotic spindle
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a cytoskeletal machine composed of microtubules and associated proteins. it provides the driving mechanical force that separates sister chromatids in mitosis
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what happens during prophase
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the mitotic spindle appears to push the centrosomes away from each-other. the centrosomes are actually propelled toward opposite ends of the cell by lengthening of the microtubules between them.chromosomes condense, with sister chromatids joined together
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what happens during prometaphase
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the nuclear envelope fragments
microtubules from the spindle interact with the chromosomes |
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what is kinetochore
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a large protein complex that assembles on the centromeric DNA of each sister chromatid
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what happens during metaphase
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the chromosome settles midway between the 2 poles of the cell, the metaphase plate
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what happens during anaphase
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sister chromatids are suddenly separated and each is pulled toward the pole to which it is attached by spindle fibers. each can now be considered a chromosome
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what are cohesions
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proteins that hold sister chromatids together
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what does the anaphase promoting complex (APC) do
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it triggers the proteolytic cleavage of cohesions that hold sister chromatids together. its hydrolyzed by separase which is inactive b4 this point (its bound to inhibitory subunit securin)
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what is the spindle checkpoint
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when all chromatids are connected to the spindle, securin is hydrolyzed, separase breaks down the cohesion
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what happens during anaphase A
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the kinetochores are pulled apart, as kinetochore MT's depolymerize
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what happens during anaphase B
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the poles themselves move apart, as polar MT's slide past one another
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what happens during telophase
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2 nuclei begin to form, surrounded by the fragments of the parent's nuclear envelope. chromatin becomes slightly less coiled. cytokinesis (division of cytoplasm) begins. spindle apparatus disassembles, MT's reform cytoskeleton. nucleolus reappears in each new nucleus; golgi, ER reappear
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how does cytokinesis occur in animal cells
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by cleavage, forming a cleavage furrow
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what happens during cytokinesis in a plant cell
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a cell plate forms
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what is a checkpoint
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the process by which an incomplete upstream even generates a signal that inhibits the initiation of downstream events.
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where the the 3 major checkpoints in the cell cycle
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G1,G2,M
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if the cell proceeds past a checkpoint what may occur?
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-insufficient cell size
-incomplete chromosome replication -incomplete attachment of chromosomes to microtubules |
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what is the G0 phase
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the non-dividing resting state; most humans are in this state
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what are the molecules that induce progression through the cell cycle
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cyclically activated protein kinases
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what are the 2 types of proteins involved in cell cycle control
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cyclins & cyclin dependent kinases (Cdks)
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what is Mpf
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a Cdk complex that acts at the G2 checkpoint as the go ahead signal for mitosis to begin
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what effects does activated MPF have that trigger M phase?
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-phosphorylates nuclear lamins
-phosphorylates chromosomal proteins -phosphorylates microtubule-associated proteins -phosphorylates an enzyme that degrades cyclin |
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what makes a benign tumor
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when abnormal cells remain at the original site
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what makes a malignant tumor
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when abnormal cells invade surrounding tissues and can metastasize, exporting cancer cells to other parts of body
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how are living organisms distinguished
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by their ability to reproduce their own kind
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what is heredity
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the transmission of traits from one generation to the next
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what is genetics
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the scientific study of heredity and variation
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what are genes
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units of heredity
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whats a life cycle
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the generation to generation sequence of stages in the reproductive history of an organism
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where does meiosis occur
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only in germ cells & cells that give rise to sperm & egg
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what does meiosis do
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it reduces the chromosome # by half, enabling sexual recombination to occur
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what are homologous chromosomes
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matching chromosomes with similar but not identical DNA nucleotide sequence, have the same length, centromere position, & genetic loci
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what are alleles
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alternate forms of a gene
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how are sex chromosomes distinguished form all other chromosomes
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by being non homologous
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what a karyotype
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an ordered display of the pairs of chromosomes from a cell
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what happens during prophase I
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chromosomes begin to condense. in synapsis, homologous chromosomes loosely pair up, aligned gene by gene
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what indicates that crossing over has occured
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presence of chiasma
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what happens at metaphase I
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paired homologous chromosomes line up at the metaphase plate, which one chromosome facing each pole. kinetochore microtubules attach to 1 of the 2 homologous chromosomes, so that one homologous chromosome will be drawn to one pole, and the other homologue to the other pole
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what happens at anaphase I
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pairs of homologous chromosomes separate. sister chromatids remain attached at the centromere and move as one unit toward the pole
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when does cytokinesis occur
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simultaneously with telophase I
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what happens during prophase II
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a new spindle apparatus forms in each cell, and the nuclear membrane breaks down.
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what happens during metaphase II
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a completed spindle apparatus is in place in each cell. kinetochore microtubules from opposite poles attach to opposite sides of the same centromere
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what happens in telophase II
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the nuclear membranes reform around 4 different clusters of chromosomes, and the chromosomes begin de-condensing. cytokinesis separates the cytoplasm
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what are the 3 events unique to meiosis
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-synapsis and crossing over in prophase I
-at the metaphase plate, there are paired homologous chromosomes, instead of individual replicated chromosomes -at anaphase I, it is homologous chromosomes instead of sister chromatids, that separate & are carried to opposite poles of the cell |
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what is parthenogensis
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development of an adult from an unfertilized egg which undergoes a mitotic division to become a diploid cell
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what 3 mechanism contribute to genetic variation
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-independant assortment of chromosomes
-crossing over -random fertilization |
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what is independant assortment
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the results of alternative arrangements of maternal & paternal homologous chromosome pairs on the metaphase plate in meiosis I
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what happens in crossing over
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homologous portions of 2 nonsister chromatids trade places
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what is random fertilization
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which 2 gametes fuse into a zygote is a matter of chance
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what does natural selection result in
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accumulation of genetic variations favored by the environment
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what does the DNA repair hypothesis state
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only diploid cells can effectively repair certain kinds of chromosomal damage
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what is cancer
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a growth disorder of cells
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what are tumors characterized by
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deregulation of cell division and cell death
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what is tumorigenesis
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a multi-step process driven by multiple genetic alterations that progressively transform normal cells into malignant cells
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what 6 acquired capabilities do cancer cells have
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-growth cell autonomy
-evasion of growth inhibitory signals -evasion of apoptosis -unlimited replicative potential -angiogenesis -invasion and metastasis |
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what are the genes that normally regulate cell growth and division during the cell cycle
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-genes for growing factors
-their receptors -intracellular molecules for signaling pathways |
