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Exam 4 - Flashcards

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Class:BIOL 23100 - Biology III: Cell Structure And Function
Subject:BIOL-Biological Sciences
University:Purdue University - Main Campus
Term:Fall 2010
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2 uM pure actin plus accessory protein 2' lag phase, then steady polymerization until 85% of actin is in filaments ave length 2 u Severing
2 uM pure actin plus accessory protein no lag phase, then steady polymerization until 90% of actin is in filaments ave length 5 u Nucleating
2 uM pure actin plus accessory protein 2' lag phase, then steady polymerization until 60% of actin is in filaments ave length 5 u Monomer-seq
2 uM pure actin plus accessory protein 2' lag phase, then steady polymerization until 90% of actin is in filaments ave length 5 u intersect each other Cross-linking
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Actin Based Lamellipodium and muscle sacromere
Microtubule based Cillararly or flagellar axenon and mitotic spindle
It is highly stable, typically persisting for the life of the cell Cilaraly, flagella, muscle sacromere
It is labile, typically assembling, disassembling and reassembling repeatedly during the life of the cell Lamellipodium and mitotic spindle
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Its function relies at least in part on dynein-like motor proteins Mitotic spindle and ciliary or flagellar axonenoneme
Its function relies on constant actin assembly and disassembly Lamellipodium
Its function relies on myosin “thick filaments Muscle Sacromere
Regulates the interactions of myosin with the actin in the muscle sarcomere ATP and Tropomyosin
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A plus end directed molecular motor Myosin and Kinesin
A minus end directed molecular motor Dynein
Binds and hydrolyzes ATP Actin, myosin, kinesin, dyenin
Binds and hyrolyzes GTP Beta tubulin
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Assembles into bipolar filaments Intermediate filament proteins Myosin
Assembly of this protein into filament is regulated by phosphorylation by a specific kinase Intermediate filament protein Myosin
What is the critical concentration for actin assembly in the control experiment At steady state 80%, the actin assembled , 20% remains as a monomer Total actin concentration = 1 microliter Cc= 1 micrometerer * .2=.2 micrometer
What one feature of the plot from Expt #2 suggests to you that Factor A has actin filament nucleating activity? THere is no lag phase
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You know from other experiments that you have performed in your lab that, in addition to enhancing actin nucleation, Factor A binds to the ends of actin filaments. What one feature of the plot from Expt #2 suggests to you that Factor A has actin filament capping activity? The % of f-actin at steady-state is different in experiment #2 [note also that the slope is shallower, so the assembly rate is slower]
Which end of the actin filament, the (+) end or the (-) end, is capped by Factor A? The plus end because there is less f-actin (or a higher critical concentration) at steady-state
Expt #3 shows that 1 mM of Factor B increases the lag time and reduces the overall rate of actin polymerization. Based on the data gathered in this experiment (plotted on the curve labeled “Factor B”), what is the effect of Factor B on critical concentration? Choose one: decreases, increases, no effect, or unknown The effect is unknown because actin had not reached steady-state in experiment #3.
During the prometaphase. The chromosome on the left of the diagram (labeled “2") has active dynein motor proteins operating. WHICH DIRECTION is it moving relative to the left pole? Toward the pole
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Prometaphase The chromosome on the right of the diagram (labeled “3") is moving away from the right spindle pole. WHAT KIND of motor proteins is it using? kinesins [plus-end-directed MT motors]
Prometaphase The area of microtubule overlap labeled “1" is drawn with a motor protein present. WHAT KIND of motor protein is it, and WHAT SPECIFIC MOVEMENT is it producing? A kinesin motor [here, a bipolar kinesin] is driving pole separation
Methaphase On the kinetochores (in the region labeled “5") WHAT KIND of active motor proteins are interacting with the chromosomal microtubules? In which direction are they pulling the kinetochores (TOWARD or AWAY FROM the poles)? minus-end-directed motors (or dyneins) are working to pull the kinetochores toward the poles
Metaphase What would happen to this metaphase spindle if we cut all the CHROMOSOMAL microtubules, midway between the kinetochores and the poles, with a laser? The poles would separate
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Metaphase What would happen to this metaphase spindle if we cut all the POLAR microtubules, midway between the overlap zone (labeled “4") and the poles? The poles would move closer together
Which end of each chromosomal microtubule is undergoing net assembly and which end is undergoing net disassembly? Net assembly at the plus ends, net disassembly at minus ends
Definition
Anaphase During metaphase, the chromosomal microtubules were treadmilling, and maintained a constant length. Now, during anaphase, they are shortening as the chromosomes approach the poles. EXPLAIN how the properties of the plus and minus ends of the chromosomal microtubules have changed between metaphase and anaphase: The minus ends are now capped, and the plus ends are depolymerizing.
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Anaphase B, or spindle pole separation, can make a major contribution to the total distance that the daughter chromosomes separate. In the diagram above, CIRCLE the motor proteins responsible for anaphase B movement, and in the box below, STATE what kind of motor proteins they are. kinesins, or plus-end-directed motors [bipolar in this diagram]
TIGHT JUNCTIONS Impermeability: they bring the plasma membrane of adjacent cells into such close apposition that even small molecules can’t leak between the cells. This allows epithelia to maintain solute gradients between their apical and basal sides.
Adherens Junctions Cell-cell adhesion and signaling: they connect adjacent cells and interact with F-actin at their cytoplasmic sides. They are also sites of cell signaling.
DESMOSOMES Cell-cell adhesion & mechanical strength: they connect adjacent cells and interact with IFs at their cytoplasmic sides. This creates a mechanical continuum across many cells and confers on epithelia much of their resistance to disruption.
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HEMIDESMOSOMES Adhesion of cells to the ECM: they connect cells to the underlying ECM (or basal lamina), and interact with IFs at their cytoplasmic side. (
Na+/K+ ATpase Hemidesmosomes
Na+/glucose symporter Tight junctions
Glucose transporter Hemodesmosomes
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Cadherins Adherins,Desmosomes
Integrins Hemidesmosomes
Cells of this strain do not divide. Although they grow in size their chromosomes never condense, and they are apparently stuck in S phase. The cells die after a few days. The G1/start cyclin cannot be degraded by protease.
Cells of this line get larger with each round of division and die out after several cell cycles It pauses at the G2/M checkpoint until the cell volume has increased 3-fold since the last cell division
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Cells of this strain do not divide. They grow in size and completely duplicate their DNA, but they can’t enter M – they do not even undergo nuclear envelope breakdow The G2/M cyclin cannot bind to the cell cycle kinase.
Definition
Cells of this strain get smaller and smaller with each round of division and die after several cell cycles. Crosses the G2/M cell cycle checkpoint before the cell has doubled in volume since the last cytokinesis
yeast cells manage to move through the cell cycle with a smaller toolkit: they have several different cyclins, each specific for a particular cell cycle checkpoint, but they have only ONE CELL CYCLE KINASE. This kinase serves at each cell cycle checkpoint, phosphorylating substrates that are unique to that checkpoint. The substrate specificity of the yeast cell cycle kinase changes depending on which cyclin it is bound to. Because there are different cyclins for different checkpoints, the kinase can phosphorylate different substrates at each checkpoint
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Epithelial cells lining your respiratory tract form a continuous sheet that acts as one of the first lines of defense against invading pathogens. One way they do this is by secreting small, microbe-killing peptides at their apical face. Which type of cell junction found in the epithelium ensures that this toxic molecule stays at the apical face, in the outside world? Tight junctions
Which of the genome-carrying pathogens is most dependent on using the host cell’s resources in order to survive? viruses (also OK: bacteriophages or phages)
What is the single most important characteristic of prions that makes them a unique infectious agent? (Answer in one sentence.) Unlike the other types of infectious agents, prions are comprised solely of protein (they do not possess nucleic acid).
(a) What is the portion of myosin that is responsible for its ability to form bipolar thick filaments? TAIL
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What is the portion of myosin that contains the enzymatic activity? MOTOR DOMAIN
What is the portion of myosin that contains the actin binding domain? MOTOR DOMAIN
What is the portion of myosin that is the primary determinant of “step size” when myosin moves along an actin filamen Neck
What is the portion of myosin that dramatically changes conformation after myosin is phosphorylated by a kinase Tail
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In the top part of the figure at right the sister chromatids are still joined, but they are about to separate and move towards opposite poles. What is the name of the structure at which the si s te r chromatids are connected? Centromere
What is the name of the structure at which the microtubules are attached to the chromosomes? Kinetechore
After separating, each chromatid moves towards one of two poles. Two forces are involved in this movement. One force is derived from the activity of a molecular motor, the other is derived from the depolymerization of specific microtubules in the mitotic spindle. Considering only the molecular motor for a moment, in what direction is this motor walking, toward the PLUS or the MINUS END of the microtubule? Minus
Based on what you have learned about microtubule and actin regulatory proteins, which one of the following is most likely to be involved in disassembly of the kinetochore microtubules? CATASTROPHIN This is the only protein out of the choices that not only PROMOTES MICROTUBULE DISASSEMBLY, but also specifically ACTS AT THE PLUS ENDS (The only other disassembly-promoting protein is stathmin, but it would act non-specifically by sequestering free tubulin dimers) Found at kinetechore
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What type of force - PULLING OR PUSHING - is produced by a MINUS END DIRECTED microtubule motor activity during Anaphase B? To WHICH PART OF THE CELL is this motor ANCHORED (attached by its tail region)? Feel free to draw on the figure above if it helps you answer the question. A PULLING force is achieved by a minus-end directed motor attached to the CELL MEMBRANE or CORTEX
The other major event during M phase is cytokinesis, or cell division, during which the cell is pinched in two by the contractile ring. Although the exact structure of the contractile ring is poorly understood, we do know that the ring contains myosin thick filaments, similar to the ones found in the muscle sarcomere. Largely because of this, we have deduced that the actin filaments in the contractile ring must be arranged in a particular way, either in parallel actin bundles (all plus ends pointing in the same direction) or in antiparallel bundles (half of the filaments pointing one way and the other half pointing the other). Which is the most likely arrangement of the actin filaments (parallel or antiparallel)? Antiparallel
Definition
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 2 uM pure actin plus accessory protein 2' lag phase, then steady polymerization until 85% of actin is in filaments ave length 2 uSevering
 2 uM pure actin plus accessory protein no lag phase, then steady polymerization until 90% of actin is in filaments ave length 5 uNucleating
 2 uM pure actin plus accessory protein 2' lag phase, then steady polymerization until 60% of actin is in filaments ave length 5 uMonomer-seq
 2 uM pure actin plus accessory protein 2' lag phase, then steady polymerization until 90% of actin is in filaments ave length 5 u intersect each otherCross-linking
 Actin BasedLamellipodium and muscle sacromere
 Microtubule basedCillararly or flagellar axenon and mitotic spindle
 It is highly stable, typically persisting for the life of the cellCilaraly, flagella, muscle sacromere
 It is labile, typically assembling, disassembling and reassembling repeatedly during the life of the cellLamellipodium and mitotic spindle
 Its function relies at least in part on dynein-like motor proteinsMitotic spindle and ciliary or flagellar axonenoneme
 Its function relies on constant actin assembly and disassemblyLamellipodium
 Its function relies on myosin “thick filamentsMuscle Sacromere
 Regulates the interactions of myosin with the actin in the muscle sarcomereATP and Tropomyosin
 A plus end directed molecular motorMyosin and Kinesin
 A minus end directed molecular motorDynein
 Binds and hydrolyzes ATPActin, myosin, kinesin, dyenin
 Binds and hyrolyzes GTPBeta tubulin
 Assembles into bipolar filamentsIntermediate filament proteins
Myosin
 Assembly of this protein into filament is regulated by phosphorylation by a specific kinaseIntermediate filament protein
Myosin
 What is the critical concentration for actin assembly in the control experimentAt steady state 80%, the actin assembled , 20% remains as a monomer
Total actin concentration = 1 microliter
Cc= 1 micrometerer * .2=.2 micrometer
 What one feature of the plot from Expt #2 suggests to you that Factor A has actin filament nucleating activity?THere is no lag phase
 You know from other experiments that you have performed in your lab that, in addition to enhancing actin nucleation, Factor A binds to the ends of actin filaments. What one feature of the plot from Expt #2 suggests to you that Factor A has actin filament capping activity? The % of f-actin at steady-state is different in experiment #2
[note also that the slope is shallower, so the assembly rate is slower]
 Which end of the actin filament, the (+) end or the (-) end, is capped by Factor A? The plus end because there is less f-actin (or a higher critical
concentration) at steady-state
 Expt #3 shows that 1 mM of Factor B increases the lag time and reduces the overall rate of actin polymerization. Based on the data gathered in this experiment (plotted on the curve labeled “Factor B”), what is the effect of Factor B on critical concentration? Choose one: decreases, increases, no effect, or unknownThe effect is unknown because actin had not reached steady-state in
experiment #3.
 During the prometaphase. The chromosome on the left of the diagram (labeled “2") has active dynein motor proteins operating. WHICH DIRECTION is it moving relative to the left pole?Toward the pole
 Prometaphase The chromosome on the right of the diagram (labeled “3") is moving away from the right spindle pole. WHAT KIND of motor proteins is it using?kinesins [plus-end-directed MT motors]
 Prometaphase The area of microtubule overlap labeled “1" is drawn with a motor protein present. WHAT KIND of motor protein is it, and WHAT SPECIFIC MOVEMENT is it producing?A kinesin motor [here, a bipolar kinesin] is driving pole
separation
 Methaphase On the kinetochores (in the region labeled “5") WHAT KIND of active motor proteins are interacting with the chromosomal microtubules? In which direction are they pulling the kinetochores (TOWARD or AWAY FROM the poles)?minus-end-directed motors (or dyneins) are working to pull the
kinetochores toward the poles
 Metaphase What would happen to this metaphase spindle if we cut all the CHROMOSOMAL microtubules, midway between the kinetochores and the poles, with a laser? The poles would separate
 Metaphase What would happen to this metaphase spindle if we cut all the POLAR microtubules, midway between the overlap zone (labeled “4") and the poles? The poles would move closer together
 Which end of each chromosomal microtubule is undergoing net assembly and which end is undergoing net disassembly?Net assembly at the plus ends, net disassembly at minus ends
  Definition
 Anaphase During metaphase, the chromosomal microtubules were treadmilling, and maintained a constant length. Now, during anaphase, they are shortening as the chromosomes approach the poles. EXPLAIN how the properties of the plus and minus ends of the chromosomal microtubules have changed between metaphase and anaphase:The minus ends are now capped, and the plus ends are
depolymerizing.
 Anaphase B, or spindle pole separation, can make a major contribution to the total distance that the daughter chromosomes separate. In the diagram above, CIRCLE the motor proteins responsible for anaphase B movement, and in the box below, STATE what kind of motor proteins they are.kinesins, or plus-end-directed motors [bipolar in this diagram]
 TIGHT JUNCTIONSImpermeability: they bring the plasma membrane of adjacent cells into
such close apposition that even small molecules can’t leak between the
cells. This allows epithelia to maintain solute gradients between their
apical and basal sides.
 Adherens JunctionsCell-cell adhesion and signaling: they connect adjacent cells and interact
with F-actin at their cytoplasmic sides. They are also sites of cell
signaling.
 DESMOSOMESCell-cell adhesion & mechanical strength: they connect adjacent cells
and interact with IFs at their cytoplasmic sides. This creates a
mechanical continuum across many cells and confers on epithelia much
of their resistance to disruption.
 HEMIDESMOSOMESAdhesion of cells to the ECM: they connect cells to the underlying ECM
(or basal lamina), and interact with IFs at their cytoplasmic side.
(
 Na+/K+ ATpaseHemidesmosomes
 Na+/glucose symporterTight junctions
 Glucose transporterHemodesmosomes
 CadherinsAdherins,Desmosomes
 IntegrinsHemidesmosomes
 Cells of this strain do not divide. Although they grow in size their chromosomes never condense, and they are apparently stuck in S phase. The cells die after a few days.The G1/start cyclin cannot be degraded by protease.
 Cells of this line get larger with each round of division and die out after several cell cyclesIt pauses at the G2/M checkpoint until the cell volume has increased 3-fold since
the last cell division
 Cells of this strain do not divide. They grow in size and completely duplicate their DNA, but they can’t enter M – they do not even undergo nuclear envelope breakdowThe G2/M cyclin cannot bind to the cell cycle kinase.
  Definition
 Cells of this strain get smaller and smaller with each round of division and die after several cell cycles.Crosses the G2/M cell cycle checkpoint before the cell has doubled in volume
since the last cytokinesis
 yeast cells manage to move through the cell cycle with a smaller toolkit: they have several different cyclins, each specific for a particular cell cycle checkpoint, but they have only ONE CELL CYCLE KINASE. This kinase serves at each cell cycle checkpoint, phosphorylating substrates that are unique to that checkpoint.The substrate specificity of the yeast cell cycle kinase changes depending
on which cyclin it is bound to. Because there are different cyclins for
different checkpoints, the kinase can phosphorylate different substrates at
each checkpoint
 Epithelial cells lining your respiratory tract form a continuous sheet that acts as one of the first lines of defense against invading pathogens. One way they do this is by secreting small, microbe-killing peptides at their apical face. Which type of cell junction found in the epithelium ensures that this toxic molecule stays at the apical face, in the outside world?Tight junctions
 Which of the genome-carrying pathogens is most dependent on using the host cell’s resources in order to survive?viruses (also OK: bacteriophages or phages)
 What is the single most important characteristic of prions that makes them a unique infectious agent? (Answer in one sentence.)Unlike the other types of infectious agents, prions are comprised solely
of protein (they do not possess nucleic acid).
 (a) What is the portion of myosin that is responsible for its ability to form bipolar thick filaments?TAIL
 What is the portion of myosin that contains the enzymatic activity?MOTOR DOMAIN
 What is the portion of myosin that contains the actin binding domain?MOTOR DOMAIN
 What is the portion of myosin that is the primary determinant of “step size” when myosin moves along an actin filamenNeck
 What is the portion of myosin that dramatically changes conformation after myosin is phosphorylated by a kinaseTail
 In the top part of the figure at right the sister chromatids are still joined, but they are about to separate and move towards opposite poles. What is the name of the structure at which the si s te r chromatids are connected?Centromere
 What is the name of the structure at which the microtubules are attached to the chromosomes?Kinetechore
 After separating, each chromatid moves towards one of two poles. Two forces are involved in this movement. One force is derived from the activity of a molecular motor, the other is derived from the depolymerization of specific microtubules in the mitotic spindle. Considering only the molecular motor for a moment, in what direction is this motor walking, toward the PLUS or the MINUS END of the microtubule?Minus
 Based on what you have learned about microtubule and actin regulatory proteins, which one of the following is most likely to be involved in disassembly of the kinetochore microtubules?CATASTROPHIN
This is the only protein out of the choices that not only PROMOTES
MICROTUBULE DISASSEMBLY, but also specifically ACTS AT
THE PLUS ENDS (The only other disassembly-promoting protein is
stathmin, but it would act non-specifically by sequestering free tubulin
dimers)

Found at kinetechore
 What type of force - PULLING OR PUSHING - is produced by a MINUS END DIRECTED microtubule motor activity during Anaphase B? To WHICH PART OF THE CELL is this motor ANCHORED (attached by its tail region)? Feel free to draw on the figure above if it helps you answer the question.A PULLING force is achieved by a minus-end directed motor attached to
the CELL MEMBRANE or CORTEX
 The other major event during M phase is cytokinesis, or cell division, during which the cell is pinched in two by the contractile ring. Although the exact structure of the contractile ring is poorly understood, we do know that the ring contains myosin thick filaments, similar to the ones found in the muscle sarcomere. Largely because of this, we have deduced that the actin filaments in the contractile ring must be arranged in a particular way, either in parallel actin bundles (all plus ends pointing in the same direction) or in antiparallel bundles (half of the filaments pointing one way and the other half pointing the other). Which is the most likely arrangement of the actin filaments (parallel or antiparallel)?Antiparallel
  Definition
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