Intermediate Filaments, F-actin, Cell Mobility (Lecture 22) Flashcards
What are lysosomes?
What is autophagy?
What are vacuoles?
What are the main structural components of the cytoskelton?
Microtubules are polymers of what?
How do vesicles move along the microtubule’s track?
- Lysosomes are organelles containing hydrolytic enzymes that fuse to other vesicles and degrade their contents.
- Autophagy is a process whereby cells degrade internal components for recycling.
- Vacuoles are plant organelles that store compounds and provide structural support by turgor pressure.
- Microtubules, Intermediate Filaments and Microfilaments are the main structural components of the cytoskeleton.
- Microtubules (MT) are polymers of α and β tubulin that provide structural support and intracellular “tracks” (animals).
- Vesicles move along MTs tracks via ATP-powered motor MAPs - Kinesin and Dynein.
What are Intermediate Filaments (IF)? (detail)
- intermediate size (10-12 nm diameter)
- exclusive to multicellular animal cells
- provide structural support, mechanical strength
- stable (relative to MTs or microfilaments)
- fibrous α-helical proteins
★ NOT polar (Therefore not used for transport)
- Examples
- keratins: epithelial cells
- neurofilaments: neurons
- lamins: nucleus of cells
Neurofilaments in the axons of neurons
Intermediate filaments composed of keratins and lamins are stained what colour?
Neurofilaments in the axons of
Intermediate filaments composed of keratins in the cytoplasm are stained red.
Intermediate filaments composed of lamins in the nucleus are stained blue
What are Microfilaments (MF) and what are several important functions?
- thinnest cytoskeletal element( ~8nm)
- polymer of actin protein
- polypeptide = 42 kDa, binds ATP
- monomer = G-actin (globular)
- polymer microfilament = F-actin
- several important functions:
- maintenance of cell shape
- cell movement
- cytokinesis
- endocytosis & phagocytosis
- vesicle transport (esp. plants)
How to microfilament tracts move vesicles?
Microfilament tracks move vesicles to distant parts of root cells. Powered by MF-specific motor protein: Myosin
What is a microfilament structure?
A microfilament is a double helix of actin monomers.
MFs are Dynamic like MTs what does this mean with respect to their ends?
Microtubules and Microfilaments Are Dynamic
- The plus end assembles quickly
- The minus end assembles slowly
G-actin monomers have what kind of structure?
What about F-actin?
G-actin monomers have a polar structure.
The F-actin filament is polar: ‘plus’ and ‘minus’ ends.
What is F-actin microfilament assembly?
G-actin polymerizes reversibly
- nucleation (slow)
G-actin → dimers → trimers → short filaments
-
elongation (fast)
- monomers add to both ends
‣ faster at ‘+’ end
What is the technique of Actin Staining?
Phalloidin belongs to a class of toxins called
phallotoxins, which are found in the “Angel of
Death” mushroom (Amanita phalloides).
Ingestion of Phalloidin is lethal after a few days. Major symptom of
phalloidin poisoning is acute hunger due to the destruction of liver cells.
Phalloidin functions by binding and stabilizing filamentous actin (F-actin),
effectively preventing the depolymerization of actin filaments.
Microfilament Assembly
Polymerization/Depolymerization and Structure/Organization
- regulated by actin-binding proteins
- filaments can be loose arrays/networks or tight bundles/cables
What is regulated by actin-binding proteins?
- regulated by actin-binding proteins: Arp 2/3 complex
- Arp2/3 complex starts polymerization at branch points
F-actin networks are highly ______
Polymerization and branching provide force for?
F-actin networks are highly branched
Polymerization and branching provides force for directed cell mobility
What is Directed Cell Mobility?
Coordinated activity of actin-binding proteins controls microfilament formation in a lamellipodium to allow directed cell movement
What is myosin?
What are the two broad groups?
Myosin: a Microfilament-associated Motor Protein
- a large family of proteins
- most move toward the plus end of microfilament
- divided into 2 broad groups
-
1) conventional myosins
- type II
- primary motors for muscle contraction
-
2) unconventional myosins
- type I and types III-XVIII
- motors for cell motility
-
1) conventional myosins
Unconventional myosin generate force and contribute to motility in non-muscle cells
What are the “push” and “pull”?
Unconventional myosin generate force and contribute to motility in non-muscle cells
Actin-based protrusion of leading edge (lamellipodium) powered by actin growth “push”
Myosin-based contraction pulls trailing edge forward “pull”
Microtubule motor proteins and Microfilament-based motor proteins cooperate in what?
How do pogment granules move?
Microtubule motor proteins and Microfilament-based motor proteins cooperate in intracellular transport
Movement of pigment granules via the cytoskeleton
What are the subunits and major functions of…
a. microtubules
b. microfilaments
c. Intermediate filaments
What is the function of the nucleus?
Functions
- storage, replication, and repair of genetic material
- expression of genetic material
- transcription
- mRNA, tRNA, rRNA
- splicing
- ribosome biosynthesis
