Biology 1113 – Chapter 12 – Flashcards

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How do cells replicate?
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1) copying DNA 2) separating copies 3) dividing cytoplasm to create two complete cells
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chromosome
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("colored-body") gene-carrying structure containing DNA and associated proteins (threadlike structures)
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histones
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single long DNA double helix that is wrapped around proteins
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gene
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region of DNA that codes for a particular protein or RNA
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chromatid
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each of the double-stranded DNA copies in a replicated chromosome (before mitosis, they are joined along their length by proteins called cohesins)
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centromere
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region of a replicated chromosome where the two sister chromatids are joined most tightly and the kinetochore is formed during M phase
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sister chromatids
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chromatid copies that remain attached at their centromere
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M phase (mitotic)
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phase of the cell cycle during which cell division occurs
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interphase ("between-phase")
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- portion of the cell cycle between one M phase and the next - no dramatic changes - cells spend most of its time here - includes G1, S, and G2
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S (synthesis) phase
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DNA is synthesized for the replication of chromosomes
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cell cycle
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orderly sequence of events that leads a eukaryotic cell through the duplication of its chromosomes to the time it divides
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when are "gap" phases?
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before and after S phase
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G1 phase
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- gap between end of M phase and start of S phase - first part of interphase before DNA synthesis
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G2 phase
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- gap between end of S phase and start of M phase - last part of interphase
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order of cell cycle
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M phase, G1, S, G2
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why do gap phases exist?
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- cells perform their functional roles mostly during G1 phase (multicellular organisms) - cell uses G2 to prepare for M phase
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two events of M phase
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- division of nucleus - division of cytoplasm
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cytokinesis
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- follows mitosis - divides cytoplasm of parent cell to form two daughter cells
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how chromosomes change during: G1 phase
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4 unreplicated chromosomes
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how chromosomes change during: G2 phase
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4 unreplicated chromosomes, each consisting of two sister chromatids
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how chromosomes change during: M phase (parent cell)
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replicated chromosomes condense
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how chromosomes change during: M phase (daughter cells)
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sister chromatids separate & two daughter cells are formed by cytokinesis
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chromatin
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complex of DNA and proteins (mainly histones) that compose eukaryotic organisms
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types of chromatin
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- heterochromatin (highly compact) - euchromatin (loosely coiled)
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state of chromatin during interphase
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relaxed or less condensed, forming long & thin strands
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chromosomes during mitosis
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- two sister chromatids separate to form independent daughter chromosomes - one copy of each chromosome goes to each of the two daughter cells - each cell receives the same complement of chromosomes as the parent cell had
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5 subphases within M phase
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- prophase - prometaphase - metaphase - anaphase - telophase
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prophase
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- "before-phase" - chromosomes condense into compact structures - individual chromosomes first become visible in light microscope
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spindle apparatus
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- formed during prophase - structure that produces mechanical forces that (1) move replicated chromosomes during early mitosis and (2) pull chromatids apart in late mitosis
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microtubules
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- spindle apparatus consists of this - composed of a-tubulin and b-tubulin - asymmetric (plus and minus end) - plus end is where growth occurs - minus end is where disassembly occurs
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polar microtubules
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some microtubules extend from each spindle pole and overlap with one another
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centrosome
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structure that contains a pair of centrioles
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centrioles
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small cylindrical structures contained within the centrosome near the nucleus of a eukaryotic cell
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prometaphase
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- "before the middle-phase" - nuclear envelope disintegrates - allows cytoplasmic microtubules to attach to chromosomes at kinetochores - these events define the start of this phase
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kinetochores
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protein complex that forms on chromosome during metaphase and serves as a site for microtubule attachment
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kinesin and dynein
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motors that "walk" chromosomes up and down microtubules
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metaphase
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- "middle-phase" - chromosomes migrate to the middle - lined up on imaginary plate between two spindle poles called "metaphase plate"
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astral microtubules
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hold spindle poles in place partly because of this
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anaphase
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- "against-phase" - cohesins that hold sister chromatids together at the centromeres split - each replicated chromosome is pulled apart and creates two independent daughter chromosomes - doubles number of chromosomes in cell
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movement during anaphase
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- daughter chromosomes move to opposite poles via attachment of kinetochore proteins to the shrinking kinetochore microtubules - two poles of the spindle are pushed and pulled farther apart
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telophase
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- "end-phase" - nuclear envelope reforms around each set of chromosomes - chromosomes begin to de-condense - when two nuclei form, mitosis is complete - cytoplasm must divide via cytokinesis
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result of cytokinesis
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two daughter cells
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what happens to cytoplasmic contents?
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when cell was in interphase, the contents (including organelles) increased in number or volume so that the two daughter cells each has its own nucleus and organelles
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cell plate
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flattened, sac-like structure formed in the middle of a dividing plant cell which divides the cytoplasm into two separate cells
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cleavage furrow
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- animal and eukaryotic cells - ring of overlapping actin filaments starts to contract - ring shrinks and tightens which pulls membrane with it
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binary fission
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- bacteria - genetic material is replicated and pushed into opposite sides of cell - cell divides in half - does not include mitosis
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steps of binary fission
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1. DNA is copied and protein filaments attach 2. DNA copies are separated; ring of protein forms 3. Ring of protein draws in membrane 4. Fission complete
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Is M phase controlled by regulatory molecules in the cytoplasm?
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M-phase cytoplasm contains a regulatory molecule that induces M phase in interphase cells
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M phase-promoting factor (MPF)
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- initiates M phase in oocytes - phosphorylates a number of specific proteins that initiate mitosis or meiosis - dimer
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what is MPF made out of?
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- protein kinase - cyclins
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protein kinase
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enzyme that catalyzes the transfer of a phosphate group from ATP to a target protein
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cyclins
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- concentration fluctuates throughout cycle - regulatory proteins - control of cell cycle via cyclin-dependent kinases
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cyclin-dependent kinase (cdk)
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- protein kinase subunit of MPF - functional only when bound to a cyclin - involved in control of cell cycle
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how is MPF turned on?
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MPF's cdk subunit is further regulated by two phosphorylation sites on the subunit
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how is MPF turned off?
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an enzyme complex begins degrading MPF's cyclin subunit, triggering a chain of events that deactivates it
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MPF deactivation illustrates two key concepts about regulatory systems in cells
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- negative feedback: process is slowed or shut down by one of its products - destroying specific proteins (proteasome)
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cell-cycle checkpoints
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several points in the cell cycle at which progression of a cell through the cell cycle can be regulated
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tumor
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mass of cells formed by uncontrolled cell division
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M-phase checkpoints
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pass if: - chromosomes have attached to spindle apparatus - chromosomes have properly segregated and MPF is absent
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G1 checkpoint
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pass if: - cell size is adequate - nutrients are sufficient - social signals are present - DNA is undamaged
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p53
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if DNA is physically damaged, this protein activates genes that either stop the cell cycle until the damage can be repaired or cause the cell's programmed, controlled destruction (acts as a brake on cell cycle)
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apoptosis
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self-destruction of a cell (programmed)
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tumor suppressors
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protein that prevents cell division when conditions are unfavorable
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cancer
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- disease caused by cells that divide in an uncontrolled fashion - causes disease because they use nutrients and space needed by normal cells and disrupt function of normal tissue
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cancerous cells have two types of defects related to cell division
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1) defects that activate proteins required for cell growth when they shouldn't be active 2) defects that prevent tumor suppressor genes from shutting down the cell cycle
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malignant tumor
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cancerous
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benign tumor
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noncancerous
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metastasis
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spread of cancerous cells from their site of origin to distant sites in the body
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cancer involves defects in which checkpoint?
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G1
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social control
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- cells divide in response to signals from other cells - cells are allowed to divide only when it is in the best interest of the organism as a whole
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growth factors
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- social control is based on this - polypeptides or small proteins that stimulate cell division
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Rb protein
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- key molecule that enforces G1 checkpoint - when E2F is first produced, its activity is blocked by this tumor suppressor gene
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E2F
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- key regulatory protein - when activated, it triggers the expression of genes required for S phase
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steps of G1 checkpoint
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1. growth factors arrive from other cells 2. growth factors cause increase in cyclin and E2F concentrations 3. cyclin binds to Cdk; Cdk is phosphorylated; Rb inactivates E2F by binding to it 4. Inactivating phosphate is removed, and active Cdk phosphorylates Rb 5. Phosphorylated Rb E2F 6. E2F triggers production of S-phase proteins
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cells can become cancerous when
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checkpoints and social controls fail (G1 cyclin can be overproduced or Rb is defective)
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what happens when G1 cyclins are overproduced?
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they bind to Cdk and help activate it so that Rb is continuously phosphorylated and unable to bind to E2F
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what happens if Rb is defective?
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it does not bind normally to E2F and that E2F will activate the genes that push the cell into S phase which ultimately leads to uncontrolled cell division
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Which statement about daughter cells following mitosis and cytokinesis is correct? a. They are genetically different from each other and from the parent cell. b. They are genetically identical to each other and to the parent cell. c. They are genetically identical to each other but different from the parent cell. d. Only one of the two daughter cells is genetically identical to the parent cell.
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b
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After S phase, what comprises a single chromosome? a. two daughter chromosomes b. a double stranded DNA molecule c. two single-stranded DNA molecules d. two sister chromatids
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d
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Progression through the cell cycle is regulated by oscillations in the concentration of which type of molecule? a. p53, Rb, and other tumor suppressors b. receptor tyrosine kinases c. cyclins d. cyclin-dependent kinases
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c
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Evaluate each of the following defects. Which could lead to uncontrolled growth in cancer? 1. T/F: the overexpression of MPF activity 2. T/F: a nonfunctional Rb protein 3. T/F: the overexpression of G1 cyclin 4. T/F: a nonfunctional E2F protein
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1. F 2. T 3. T 4. F
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A particular cell type spends 4 hours in G1 phase, 2 hours in S phase, 2 hours in G2 phase, and 30 minutes in M phase. If a pulse-chase experiment were performed with radioactive thymidine on an asynchronous culture of such cells, what percentage of mitotic cells would be radiolabeled 9 hours after the pulse? a. 0% b. 50% c. 75% d. 100%
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a
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