dynamic dissonants cell and developmental biology new york university david scicchitano mark siegal...
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![Page 1: Dynamic Dissonants Cell and Developmental Biology New York University David Scicchitano Mark Siegal Kris Gunsalus University of Hawaii Steve Robinow Athula](https://reader035.vdocuments.us/reader035/viewer/2022062515/56649caf5503460f949729ef/html5/thumbnails/1.jpg)
Dynamic DissonantsCell and Developmental Biology
• New York UniversityDavid ScicchitanoMark SiegalKris Gunsalus
• University of HawaiiSteve RobinowAthula Wikramanayake
• University of Wisconsin, MadisonBrian Manske
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• Part I: structure, assembly and dynamics of microfilaments
• Part II: the cytoskeleton organizes the cytosol and supports the function of other cellular organelles and processes
• Part III:cytoskeletal filaments form higher-order structures that perform diverse functions
Actin Cytoskeleton Teachable Unit
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• Chemical principles govern the behavior of biological macromolecules.
• Cellular phenomena reflect the collective action of populations of molecules.
• The same molecule can have multiple, diverse functions within cells.
Teaching Challenges
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Diseases of the cytoskeleton• Muscular Dystrophy Dystrophin
– muscular degeneration
• Kartagener Syndrome
Axonemal dynein intermediate chain– Infertility due to defective sperm motility – Situs inversus
• Usher Syndrome myosin VII– deafness
• Epidermolysis bullosa and bullosa pemphigoid keratin mutation or autoimmune disorder
– skin blistering
Actin
Actin
Microtubules
Intermediate filaments
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Are microfilaments the same as F-actin?
A. YesB. No
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What polymerizes to form microfilaments?
A. alpha-tubulin
B. intermediate filaments
C. beta-tubulin
D. G-actin
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The cytoskeleton is composed of:
A. microtubules
B. microfilaments
C. intermediate filaments
D. A and B
E. A and C
F. B and C
G. A, B, and C
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Are microfilaments the same as F-actin?A. YesB. No
What polymerizes to form microfilaments?
A. alpha-tubulin
B. intermediate filaments
C. beta-tubulin
D. G-actin
The cytoskeleton is composed of:
A. microtubules
B. microfilaments
C. intermediate filaments
D. A and BE. A and CF. B and CG. A, B, and C
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Are microfilaments the same as F-actin?A. YesB. No
What polymerizes to form microfilaments?
A. alpha-tubulin
B. intermediate filaments
C. beta-tubulin
D. G-actin
The cytoskeleton is composed of:
A. microtubules
B. microfilaments
C. intermediate filaments
D. A and BE. A and CF. B and CG. A, B, and C
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synonymous to
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Learning Goals
• To understand the structure, assembly and dynamics of microfilaments
• Apply chemical principles to enhance understanding of actin polymerization
• Predict and understand a biological model of actin polymerization
• Predict and interpret experimental results
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G-actin: globular monomerF-actin: filamentous polymer
G-actin F-actin
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Experiment
G-Actin
+
ATP
G-Actin
I
Results
F-actin is present in I only (at steady state)
II
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Additional Experiment
G-Actin
+
ATP*
G-Actin
+
ADP
A. No F-actin in eitherB. F-actin in bothC. F-actin in ID. F-actin in II
ATP* cannot be hydrolyzed to ADP
I II
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Actual Results
G-Actin
+
ATP
G-Actin
G-Actin
+
ATP*
G-Actin
+
ADP
Amount of F-actin at steady state+++ - +++ ++
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Conclusion
For G-actin to form F-actin:
A. ATP hydrolysis is necessary.
B. ATP is necessary.
C. ADP is necessary.
D. Either ATP or ADP is necessary.
E. Neither ATP nor ADP is needed.
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APPP
APP
F-actin
G-actin
Fast Slow
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Summary
1.G-Actin has four lobes and an ATP binding site
2.In a test tube, add magnesium, sodium, potassium and either ATP or ADP:
G-actin F-actin
3. ATP binding to G-actin provides the best conformation to promote F-actin assembly
4. F-actin has directionality (the two ends are not the same)
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G-actin ↔ F-actin ATP
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Actin Dynamics
ATP
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G-actin ↔ F-actin ATP
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Summary
• G-actin and F-actin will reach a steady state.
• The nucleation step is slow.
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Acknowledgements
Thanks to our facilitators!
• Randy Phillis
• Lauren Gollahon