BI203 Lecture 19: Cytoskeleton - Actin Structure/Organization Flashcards
_____ - The structural scaffold that holds all of the cellular organelles in place.
cytoskeleton
Three main types of filaments making up the cytoskeleton:
microtubules, intermediate filaments, microfilaments
Cytoskeleton Major Functions:
1) Cell _____ /_____ and mechanical resistance to deformation.
2) Cell _____.
3) Cell _____ /_____.
4) Segregates _____ during cell division.
5) Scaffold for _____ and _____ transport.
shape, structure, movement, signaling, endocytosis, chromosomes, vesicle, organelle
The cytoskeleton is a network of protein _____ extending throughout the cytoplasm of eukaryotic cells.
It provides a structural framework that determines cell _____, positions of _____, and general organization of the _____.
The cytoskeleton is also responsible for _____ of entire cells, and internal _____ of organelles and other structures.
It is not rigid, but is a _____ structure that is continually reorganized as cells move and change shape.
filaments, shape, organelles, cytoplasm, movement, transport, dynamic,
The major cytoskeletal protein of most cells: ~_____% of total protein in the cell.
10%
Actin polymerizes to form actin filaments, or _____.
microfilaments
_____ polymerizes to form actin filaments (microfilaments).
actin
_____ _____ monomers have tight binding sites that mediate head-to-tail interaction.
globular actin
_____ _____ can grow at both ends and has polarity.
filamentous actin
Each actin monomer (_____ _____) has tight binding sites that mediate head-to-tail interactions with two other actin monomers, to form filaments (_____ _____).
globular (G) actin, filamentous (F) actin
All the actin monomers are oriented in the same direction, so actin filaments have _____.
This is important in their assembly and in establishing the direction of _____ movement relative to actin.
polarity, myosin
_____ is the first step of actin polymerization — Dimers and trimers are formed, then monomers are added to either end.
*Note: Actin polymerization is _____; the filaments can be broken down when necessary.
nucleation, reversible
_____ _____ regulate assembly and disassembly of actin filaments, cross-linking into bundles and networks, and associations with other cell structures.
actin-binding proteins
Actin bound to _____ associates with the rapidly growing barbed end.
ATP is then hydrolyzed to ADP.
ADP-actin dissociates _____ rapidly from filaments than ATP-actin.
Results in _____, where _____ is added at the barbed end while _____ dissociates from the pointed end.
ATP, more, treadmilling, ATP-actin, ADP-actin
_____ - bind ATP-actin and nucleate initial polymerization of long unbranched actin filaments.
formins
_____ - binds actin monomers and stimulates exchange of bound ADP for ATP, increasing the local concentration of ATP-actin.
profilin
_____ _____ (actin-related proteins) - initiates growth of branched actin filaments, important in driving cell movement at the plasma membrane.
Arp2/3 complex
_____ stabilize actin filaments by binding lengthwise along the groove of the filament.
_____ _____ stabilize actin by binding to the barbed or pointed ends.
tropomyosins, capping proteins
Other actin-binding proteins remodel or modify existing filaments.
_____ severs filaments, generating new ends which are then available for polymerization or depolymerization.
cofilin
The actin-binding proteins act together to promote rapid turnover of filaments and remodeling of the cytoskeleton needed for cell _____ and changes in cell _____. Their activities are controlled by signaling mechanisms in response to environmental signals.
movement, shape
Actin filaments are organized into: _____ _____ and _____ _____.
actin bundles, actin networks
_____ _____ — filaments are cross-linked into parallel arrays.
actin bundles
_____ _____ — filaments are cross-linked in arrays that form 3-D meshworks with the properties of semisolid gels.
actin networks
Actin bundles attach to the plasma membrane and anchor the cell at regions of _____ _____.
cell-cell contact
