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Advanced Cell Biology
Recitation 1: Cytoskeleton
6th March 2017
ACB-RECITATION I
Session
Meeting 2
date
(March 2nd)
papers
Brown & Berg 1974
Gardiner & Atema 2010
Recitation 1
(March 6th)
Alberts Essentials Chapter 17
Alberts Chapter 16
Pollard et al. 2007
Cytoskeleton; the internal scaffolds of the cell and engines of migration
Meeting 3
Meeting 4
(March 7th)
(March 9th)
Loisel et al. 1999
Theriot & Mitchison 1991
Watanabe & Mitchison 2002
Recitation 2
(March 13th)
Renkawitz & Sixt 2011
Force transmission: converting cytoskeletal dynamics into movement,
Signaling & Polarity in migrating cells from different systems
Meeting 5
Meeting 6
Recitation 3
(March 14th)
(March 16th)
(March 20th)
Suter et al. 1998
Parent et al. 1998
Albert Essentials Chapter 16
Alberts Chapter 15
Weiner 2002
Signaling & Polarity in migrating cells from different systems
Meeting 7
(March 21st)
Ming et al. 2002
Meeting 8
(March 23rd)
Yang et al. 2015
Recitation 4
(March 27th)
Alberts Chapter 16
Ridley et al. 2003
Signaling & Polarity in migrating cells from different systems ,
Collective Cell Migration of cells in vivo
Meeting 9
Meeting 10
Recitation 5
(March 28th)
(March 30th)
(April 3rd)
Xu et al. 2003
Miller et al. 2002
Friedl & Gilmour 2009
Collective Cell Migration of cells in vivo
Meeting 11
(April 4th)
Recitation 6
Meeting 12
(April 24th)
(April 25th)
Venkiteswaran et al. 2013
Dona et al. 2013
wrap up !
None
Wang et al. 2010
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ACB-RECITATION I
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Part I:
Match each definition below with its term from the list below (Albert Cell Bio, Chapter 16).
1. Cytoskeleton > System of protein filaments in the cytoplasm of a eukaryotic cell
that gives the cell its shape and the capacity for directed movement.
2. Protofilament > A linear filaments in the cytoplasm of a eukaryotic cell that gives
the cell its shape and the capacity for directed movement.
3. Dynamic instability > The property of sudden conversion from growth to
shrinkage, and vice versa, in a protein filament such as a microtubule or an actin
filament.
4. Treadmilling > The process by which a polymeric protein filament is maintained
at constant length by addition of protein subunits at one end and loss of subunits
at the other.
5. Myofibril > Long, highly organized bundle of actin, myosin, and other proteins in
the cytoplasm of muscle cells that contracts by a sliding-filament mechanism.
6. Myosin > motor protein in muscle that generates the force for muscle contraction.
7. Stress fibers > contractile actin bundles along with non-muscle myosin II in non-muscle
cells that are important for cellular contractility, cell adhesion and migration.
8. Axoneme > A microtubule-based structure inside cilia and flagella that is a ring of nine
outer microtubule triplets.
9. Centriole > Short cylindrical array of microtubules, a pair of which are embedded
in major microtubule-organizing center of an animal cell.
10. Dynein > Minus-end directed motor that moves along microtubules by walking
toward the minus end.
11. Kinesin > Plus-end directed motor that moves along microtubules by walking
toward the plus end.
12. Chemotaxis > The movement of an organism in response to a chemical stimulus.
13. Blebbing > A bulge, or protrusion of the plasma membrane of a cell, generated
when the actin cortex undergoes actomyosin contractions.
14. Lamellipodium > Essentially a one-dimensional structure that protrudes from a
cell and contains a core of long, bundled actin filaments.
15. Filopodium > Flattened two-dimensional protrusion of membrane, supported by
a meshwork of actin filaments, that is extended from the leading edge of crawiling
epithelial cells, fibroblast,….
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ACB-RECITATION I
Part II:
The schematic figure below illustrates the dynamics of actin cytoskeleton at cell cortex.
Explain what happens in each step and which molecules are involved there?
(Pollard et al. 2007)
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ACB-RECITATION I
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Part III: thought problems (Albert Cell Bio, Chapter 16)
Question 3-1:
If each type of cytoskeletal filament is made up of subunits that are held together by weak
noncoavalent bonds, how is it possible for a human being to lift heavy objects?
Question 3-2:
A typical time course of polymerization of actin filaments from actin subunits is shown in
Fig. 1.
Fig. 1: Formation of actin filaments over
time, starting with purified actin
monomers that are labeled with a
fluorescent probe. The three phases of
polymerization are indicated as A, B, and
C.
a. Explain the properties of actin polymerization that account for each of the three
phases of polymerization curve.
b. How would the curve change if you doubled the concentration of actin? Would the
concentration of free actin at equilibrium be higher or lower than in the original
experiment, or would it be the same in both?
Question 3-3:
Dynamic instability causes microtubules either to grow or to shrink rapidly. Consider an
individual microtubule that is its shrinking phase.
a. What must happen at the end of microtubule in order for it to stop shrinking and
start growing?
b. How would an increase in tubulin concentration affect this switch from shrinking
to growing?
c. What would happen if GDP, but not GTP, were present in the solution?
d. What would happen if the solution contained an analog of GTP that could not be
hydrolyzed?
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ACB-RECITATION I
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Question 3-4:
A solution of pure abtubulin dimers is thought to nucleate microtubules by forming a
linear protofilament about seven dimers in length. At that point, the probabilities that the
next αß-dimer will bind laterally or to the end of the protofilament are bound equal. The
critical event for microtubule formation is thought to be the first lateral association
(Fig.2).
How does lateral association promote the subsequent rapid formation of a microtubule?
Fig. 2: Model for microtubule nucleation b pure αß-tubulin dimers.
Question 3-5:
In an experiment, microtubules were grown from centrosomes at a tubulin concentration
of 25 uM. The centrosomes were then diluted into lower concentartions of tubulin, and
the number and the length of microtubules were plotted as a function of time (Fig. 3-5),
This experiment revealed that when diluted to 7.5 uM tubulin, the number of
microtubules attached to each centrosome decreased with time, and the average length of
the remaining microtubule increased. At neither 15 uM nor 5 uM did both these changes
occur.
Which interoperation best accounts for the decrease in microtubule number and the
increase in length upon dilution to 7.5 uM tubulin?
a. After dilution, some microtubules continue to hydrolyze GTP, which allows them
to continue to grow from their plus ends.
b. After dilution, the tubulin concentration is below the critical concentration for
plus-end growth, so some microtubules shrink.
c. At lower tubulin level, microtubules with a GTP cap continue to grow, but those
with a GDP cap rapidly depolymerize.
d. from the centrosome, some microtubules from the centrosome, allowing them to
rapidly depolymerize from their minus ends.
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