LEC 39 Cytoskeleton & Cell Movement Flashcards
How many G actin molecules are needed to nucleate polymerization of an F-actin filament?
3 (trimer)
What are the two ends of actin filament called?
Pointed end (minus) and barbed end (plus)
What is epidermolysis bullosa simplex?
point mutations in keratin 5 or keratin 14 that disrupt the filaments in the basal cells of the stratified epithelium, causing mechanical fragility and cellular rupture with mild trauma, resulting in blisters
Mutations in keratin 1 or keratin 10 results in what?
cause cell rupture in the middle layers of the epithelium where they are expressed
hyperkeratosis
Experiments such as the mouse model of epidermolysis bullosa simplex reveal what about intermediate filaments?
show that the main role of intermediate filaments is to maintain the structural integrity of cells and tissues
How do integrins convert from the closed to open state?
2 ways
- Binding of an extracellular ligand to the head
- OR an activated signal transduction protein (such as talin) to the cytoplasmic domains
Explain rolling with respect to leukocytes.
- Endothelial cells at the site of inflammation respond to cytokines by rapidly expressing P-selectin on their surface
- Leukocytes’ Selectin ligand binds P-selectin
- Leukocyte begins to roll (pushed by blood flow) & break and reform those bonds
- During rolling, PAF (platelet activating factor) on endothelial cell interacts w/ its receptor on leukocyte causing the αLβ2 integrin on leukocyte surface to open (activated)
- αLβ2 integrin then binds tightly to ICAM 1&2 on endothelial surface
- Rolling stops & leukocyte migrates from blood to the inflamed site
What are filopodia?
- fingerlike projections of membrane supported by a parallel bundle of actin filaments
- The bundles of F actin project into a network of actin filaments under the plasma membrane
What are the different variations of actin binding site domains for crosslinking proteins?
- The two domains are either both present in the individual protein (fimbrin)
- OR the functional crosslinker is a multimer of proteins that each have a single actin binding domain (α-actinin dimers; Spectrin tetramers).
What is the actin-binding protein that promotes nucleation of new actin filaments?
Formin
* These new filaments are unbranched
* This occurs when new actin filaments are needed to increase force during contraction
its a dimer
What do cytochalasins do?
- block the barbed end of actin filaments and prevents their elongation
- This causes cell shape changes, blocks cytokinesis, and prevents membrane protrusions
What does phalloidin do?
stabilizes actin filaments and prevents depolymerization and also is toxic and prevents movement
What are the steps of cell migration?
- Extension of the leading edge of membrane (lamellipodia or sheets of membrane, and filopodia, finger like projections of membrane) Membrane extension is thought to be aided by membrane bound myosin I
- Adhesion to the substrate often mediated by integrins
- Retraction of the trailing edge mediated by myosin II and F-actin.
In dendrites of nerves, the microtubules are oriented in which direction?
Both Directions
In the axons of nerves, which direction are the microtubules oriented?
Minus end towards the cell body and Plus end towards the synapse
What are dyneins?
“minus end directed” motor proteins that carry cargos towards the minus end of microtubules
require ATP
What are kinesins?
“plus end directed” motor proteins that carry cargos towards the plus end of microtubules.
require ATP
