Lecture #7 Flashcards
The cytoskeleton is composed of three filamentous structures: ?
Microtubules (MT)
Intermediate filaments (IFs)
Actin filaments (F-actin or microfilaments)
________ _________: Strong, flexible, ropelike fibers (10 – 12 nm in dia) that provide mechanical strength to cells that are subjected to physical stress (neurons, muscle, epithelial)
Intermediate Filaments
Intermediate Filaments are chemically _________ group of structures (70 different genes)
heterogeneous
Intermediate filaments are divided into five major classes:
4 classes are ______
1 is associated with the _____ ______ (Lamins)
cytoplasmic, nuclear envelope
Intermediate filaments are often interconnected to other cytoskeletal filaments by thin, wispy cross-bridges consisting of a dimeric protein called ______.
plectin
Each _____ dimer has a binding site for an IF at one end and a binding site for another intermediate filament, F-actin, or microtubule at the other end
plectin
Common Intermediate Filament architecture:
1. Each monomer has a ____ of globular terminal domains separated by a long fibrous alpha-helical region (polar)
2. Pairs of _________ are associated in parallel orientation to form dimers (polar)
3. Dimers associate in an anti-______, staggered fashion to form tetramers (none polar)
4. 8 _______ associate to form a unit length of the IF (none polar)
5. These unit lengths associate with one another in an end-to-end fashion to form the _______ intermediate filament (none polar)
pair, monomers, parallel, tetramers, elongated
Unlike microtubules and F-actin, none of the assembly steps of IFs require the direct involvement of either ____ or ____. Once assembled, the subunits are not incorporated at one end of the filament but into the filament’s _______.
ATP, GTP, interior
Unlike the other two major cytoskeletal elements, assembly and disassembly of IFs are controlled primarily by subunit phosphorylation and ____________.
dephosphorylation
________ containing IFs – structural proteins of epithelial cells
Keratin
IF radiate through the ______, tethered to the nuclear envelope in the _____ of the cell, and anchored at the outer edge of the cell by desmosomes and hemidesmosomes. IFs are also connected to microtubules and F-actin. They function to organize and maintain cellular _______ and absorb mechanical _____
cytoplasm, center, architecture, stress
___________ (NFs) – Bundles of IFs are located in the cytoplasm of mature neurons – oriented parallel to the axon
Neurofilaments
___________ of NFs is seen in several human neurodegenerative disorders such as Parkinson’s disease. These NF aggregates may block axonal transport on microtubules leading to neurons _______
Aggregation, death
______ filaments (F-actin, microfilament) are the third major type of cytoskeletal element that is involved in intracellular motility
Actin
__-_____ is a flexible, helical filament composed of actin monomers (the most abundant protein in most cells) and is a two-stranded structure with two ______ grooves running along its length.
F-actin, helical
Actin filaments help determine: ?
Cell shape
Intracellular mobility of organelles (vesicles)
Cell motility (growing axon)
Depending on their activity, actin filaments can be organized into: ?
ordered arrays
highly branched networks
tightly anchored bundles
All actin monomers within an actin filament are pointed in the ____ direction, resulting in a _____ filament with so-called “barbed” or (+) end and “pointed” or (-) end.
same, polar
Actin protein is
- A major contractile muscle ______
- A major protein in every _______ cell
protein, eukaryotic
Before it is incorporated into a filament, an _____ monomer binds an ATP molecule
actin
_____ is an ATPase, just as ________ is a GTPase
Actin, tubulinβ
The _____ nucleation event in filament formation occurs slowly in vitro, whereas the subsequent stage of filament elongation occurs much more ______. (just like microtubules
initial, rapidly