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BIO 221 Chapter 9
Terms in this set (61)
The ___________ is an elaborate interactive network of filamentous structures inside a cell
The cytoskeleton is composed of:
Microtubules, Microfilaments, and Intermediate filaments
Major functions of the cytoskeleton
Serves as a scaffold providing structural support (Maintains shape and resists forces); Serves as an internal framework to organize organelles within the cell; Serve as a network of tracks to direct the movement of materials and organelles within the cell; Generate force to move cells from one place to another; An essential component of the cell's division machinery
Long, hollow, relatively rigid, unbranched tubes
Components of mitotic spindle, core of cilia and flagella
Wall of microtubule is composed of ____ ______________.
Aligned parallel to the long axis of the microtubule in a circular pattern forming the wall
How are protofilaments held together?
non covalent interactions
How are protofilaments assembled?
Each protofilament is assembled from dimeric building blocks of α-and ß-tubulin subunits. Organized in a linear array along the long axis of each protofilament. Render polarity for the protofilaments. Βeta-tubulin end is the plus end. Αlpha-tubulin end is the minus end.
Microtubule-associated proteins (MAPs)
a class of proteins that participate in the regulation of microtubule assembly and function
MAPs comprise a group of proteins
One domain attaches to the surface of the microtubule and another domain projects outward as a tail
How do Microtubule associated proteins increase their stability and promote their assembly?
MAPs attach to the surface of microtubules make cross-bridge connecting among microtubules
Microtubules as Structural Supports and Organizers
I.To provide mechanical support
II.To maintain the internal organization of cells
The distribution of _______________ determines the shape of the cell
Microtubules as Agents of Intracellular Motility
III. Microtubules facilitate movement of vesicles between compartments
Axonal transport of a motor neuron:
Axon are filled with all 3 cytoskeletal structures
Microtubules serve as tracks for the transportation of materials between the cell body and the axon
Motor proteins provide strength for the movement
_____ ________ convert chemical energy (ATP) into mechanical energy to produce force
_________ ______ move unidirectional along their cytoskeletal track in a stepwise manner
Three categories of molecular motors:
kinesin, dynein, myosin
________ ___ _______ move along microtubule tracks
Kinesin and dynein
______ moves along microfilament tracks
________ is a ____ end-directed microtubular motor based on its movement.
What does Kinesin being plus ended mean?
it binds to the beta-tubulin and move towards plus end
________ of kinesin movement is __________ related to ATP concentration
A cytoplasmic dynein molecule contains:
-Two heavy chains(Force-generating head; Microtubule binding stalk extending from the head)
-variable amount of intermediate chains and light chains
______ is a _____ end-directed microtubular motor.
Responsible for initiation and organization of microtubules in animal cells. Contains two barrel-shaped centrioles surrounded by pericentriolar material.
PCM initiates assemble of microtubules
What are microtubule organizing centers?
MTOCs are specialized structures for the nucleation (assembly) of microtubules and Initiates de novo formation of microtubules from α-and β-tubulin
___-________ __________ and _-_______ form γ-tubulin ring complex and attach to the pericentriolar material
Non-tubulin proteins and γ-tubulin
__________ begins as αβ-tubulin dimers bind to an open ring of γ-tubulin molecules
Only __-________ can bind to γ-tubulin ring
Basal body function and location
Function: Is responsible for the initiation and organization of microtubules for outer microtubules in cilia and flagella
Location: Is located at the base of the cilia or flagella
Plant cells lack ________; their microtubules are organized around the _______
MTOCs(Microtubule Organizing Centers); nucleus
Function of MTOCs
-Initiation of microtubule initiation
-Control the number of microtubules
-Control the polarity of microtubules
-Control the number of protofilaments that make up wall of microtubules
-Control the time and location of microtubule assembly
Microtubules are polymers that can be ____________ or _____________ as required
General characteristics of Intermediate Filaments (IF):
Radiate through the cytoplasm and nucleus only in animal cells
Solid unbranched filaments
Strong, flexible and ropelike
Composed of heterogeneous proteins
~70 proteins are identified
Interconnected to other cytoskeletal filaments by cross-bridges
Five major classes of Intermediate Filaments
classes I-IV: components for construction of filaments
type V (lamins): component of the inner lining of the nucleus
Polypeptides of IF share common structure of:
A central, rod-shaped, α-helical domain of Similar length Homologous amino acid sequence
Globular domains flank each side of the central domain with varied Length and Sequence
____ _________ interact at the central domain to form a dimer aligned parallel to each other in the same orientation
two heterodimers align paralelle with one end a ____-________ on on end and an ___-_________ on the other. They possess _________.
C-termini, N-termini, polarity
Two dimers form a _______. They are aligned ____________ to each other. The tetramer has no polarity.
_____ _________ associate to form a filament
Function of intermediate filaments- Keratin
Primary structural protein for epithelial cells. Tethered to the nuclear envelop and radiate out anchoring at the outer edge of the cell by hemidesmosome and desmosome
Actin filament is also referred as ______________ or ___-_____________.
Microfilament or F-actin
Actin Filament description
Solid, thinnest cytoskeleton structure with polarity. Often organized into a branching network. Actin protein is the only component. Responsible for motility of cell and intracellular parts
ATP-bound actin monomer is the building block for ______________
___________ of microfilament in vitro requires preformed microfilament as a seed
Microfilaments have polarity
Barbed end(plus end):
~High affinity for ATP-actin monomers
Pointed end (minus end):
~Low affinity for ATP-actin monomers
Actin assembly/disassembly in vitro depends upon _____________ of actin monomers
What is critical concentration?
Critical concentration is the lowest ATP-actin monomers concentration for elongation to happen
Critical concentration of barbed (+) end is much _____ than the pointed (-) end
Concentration of ATP-Actin _________ to a level where net addition of actin monomer only to plus end
Concentration of ATP-Actin further drops to a level where net loss to the ________ end and net addition to the _____end occur
What is steady state?
Steady state is where the length of microfilament and free ATP-actin remain constant
Two types of myosin
Conventional (Type II) myosin
~Primary motors for muscle contraction
~Move toward barbed (+) end of actin filament
Unconventional (Type I) myosin
Myosin II moves along microfilament tracks _________________.
Myosin II move toward the _____ end. Actin filament is moved to the _____ end.
_________ ___ moves in a hand-over-hand fashion similar to that of the kinesin molecule, so at least one of the two heads must be bound to its polarized track at all times.
Several unconventional myosins (including myosin I, V, and VI) are associated with various types of ___________ _________ and ____________.
cytoplasmic vesicles and organelles
Function of motor proteins on actin filament
Required for splitting a cell
~Form the cell furrow during cytokinesis
Generation tension at focal adhesion and Adherensjunctions
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