Cytoskeleton Flashcards
What is actin?
Actin is a cytoskeleton protein comprised of multiple subunits arranged in trimers
What are the three phases of actin polymerization and what is the rate-limiting step?
Nucleation, Polymerization, Steady State
Rate-limiting: nucleation
What is the role of formin?
Formin catalyzes nucleation by binding the first couple monomers
What is the role of Arp 2/3?
Arp 2/3 forms branches in the actin filaments.
What is the role of ADF/cofilin?
Cofilin dissociates actin monomers and cleaves actin filaments
What is the role of profilin?
Profilin stimulates filament formation by replacing ATP with ADP on G-actin. However, actin subunit will not polymerize with profilin still bound.
What is the function of CapZ?
CapZ binds to the positive end of actin filaments and prevents new subunits from being added, this leads to filament degradation.
What is the function of Tropomodulin?
Tropomodulin binds to the negative end of actin filaments and prevents subunits from being removed, this leads to filament polymerization.
What is the function of Fimbrin?
Fimbrin binds actin filaments closely together, forming bundles
What is the function of a-actinin?
Connects actin filaments, however is more spacious than fimbrin. Allows the filaments to act as one unit and contract.
What is the function of filamen?
Filamin is responsible for connecting the actin filaments into networks.
What is the function of the WASP protein?
The WASP protein is responsible for activating Arp 2/3 and allowing it to form branches. (Used in cellular movement)
What is Wiskott-Aldrich syndrome and what is it caused by?
WAS is an immune disease caused by a defect in the WASP protein gene. It presents as a triad of thrombocytopenia, eczema, and recurring pyogenic infections. It is an x-linked recessive disease, characterized by B and T cell dysfunction.
What family of proteins makes up intermediate filaments in the epithelium?
Keratin
Describe how an intermediate filament is formed
First, two monomers line up parallel to each other to form a dimer.
Next, two of these dimers arrange anti-parallel to each other to form a tetramer.
Next, tetramers form protofilaments by lining up end to end.
Last, protofilaments group together to form a filament
What is the presentation and cause of Epidermolysis Bullosa Simplex?
EB Simplex is caused by a defect in keratin intermediate filaments located in the epithelial layer. It is the most common and mildest form, with blisters forming on the top layer of the skin at areas that typically experience a lot of friction.
Describe the structure of microtubules
Microtubules are made up of subunits of B- and a-tubulin dimers arranged in protofilaments. 13 protofilaments make up one microtubule.
What is the role of GTP in microtublule formation?
GTP is required to attach tubulin dimers to a growing microtubule. GTP is broken down into GDP and subsequently tubulin is removed from the microtubule.
What molecule is responsible for anchoring the - end of the microtubule and where is this located?
Y-tubulin forms a ring structure that anchors the microtubule at the centrosome (around the centriole)
What cancer drugs prevent polymerization of MTs?
Vincristine and Vinblastine
Disrupts the cell cycle
What is the mechanism of action for Taxol?
Taxol stabilizes microtubules so that they can’t be shrunk, freezing the cell cycle.
What is the role of polymerase in microtubule formation?
Polymerase increases the rate of assembly of microtubules by facilitating tubulin addition
What is the role of depolymerase in microtubule formation?
Depolymerase prevents the addition of new tubulin, leads to catastrophe
What is the role of CLASP?
CLASP is a protein that stops the disassembly and starts the assembly of microtubules.
How are microtubules organized in dendrites?
Orientation (+,-) is random, stabilized by MAP2
How are microtubules organized in axons?
Oriented in a way that the + end faces away from the cell body and the - end is towards the cell body, stabilized by tau.
What is Dynein?
Motor protein that moves towards the center of the cell, or - end of a microtuble
What is Kinesin?
Motor protein that moves towards the + end of a microtubule, toward the periphery of a cell
What is the structure of an axoneme?
9 Outer microtubules arranged in pairs in a circle, connected by a nexin link. Two complete microtubules located in the middle.
9+2 organization
