Cytoskeleton 1 Flashcards
What are the 3 major cytoskeletal filaments?
Microfilaments also known as actin filaments
Intermediate filaments
Microtubules
Describe the structure and distribution of actin filaments:
Thin, flexible filaments made of the protein actin and exist as 2 intertwined F-actin chains
Concentrated in the cortex providing cell structure
Distributed throughout cytoplasm
What is the function of actin filaments?
Cell shape and mechanical support
Cell motility - cell crawling
Cytokinesis
Describe the structure and distribution of microtubules:
Hollow cylinders that are composed of tubulin dimers (α-tubulin and β-tubulin)
Form protofilaments arranged in a tube shape
Extend radially from the microtubule-organizing centers (MTOCs), such as the centrosome, and span throughout the cytoplasm
What is the function of microtubules?
Intracellular transport powered by motor proteins
Cilia and flagella movement
Critical for the formation of the mitotic spindle, ensuring proper chromosome segregation during mitosis
Describe the process of nucleation
Cellular actin, in G or F forms, undergoes nucleation, a process where small actin oligomers become stable until many monomer subunits are in association
Describe actin polymerisation/ depolymerisation:
Polymerization is the process where G-actin monomers assemble into F-actin filaments
Depolymerization is the process by which F-actin filaments disassemble, returning G-actin monomers to the cytoplasmic pool
Actin filament polymerisation is faster at the plus end, requiring ATP hydrolysis.
This process occurs one monomer at a time, weakening bonds between monomers and making depolymerisation easier
This is crucial for the actin cytoskeleton’s dynamic function
Describe the nucleation and organisation of the actin cytoskeleton:
Actin filament nucleation and assembly are typically found in the cell cortex, near the plasma membrane.
The process is initiated by an actin-related protein complex (ARP), which mimics the plus end of an actin filament, allowing a stable point for filament nucleation.
The stability of actin assemblies is influenced by accessory proteins binding longitudinally or to open ends.
How are actin filaments involved in cell attachment?
Actin bundles attach to the plasma membrane to anchor cell-cell junctions and cell attachment to the underlying extracellular matrix
What are integrins and their function?
Integrins are trans-membrane receptors that mediate attachment and spreading
Function - survival signalling pathways via the focal adhesion kinase complex
How is cell migration achieved and what are the 3 steps involved?
Cell migration in mammals involves cell crawling, a process involving rapid cytoskeletal rearrangements. This involves protrusion, attachment, and traction. Protrusion involves pushing actin-rich structures out of the cell, attachment involves attaching the actin cytoskeleton to the substratum, and traction draws the trailing cytoplasm forward
Describe the polymerisation of microtubules:
Consists of 3 phases;
Nucleation - initial formation
Elongation - growth
Steady state - tubulin molecules are added and lost at the same rate
Microtubules grow
from a specific nucleating site (in most cases the
centrosome)
Describe the process of dynamic instability:
Constant addition of monomer at one end (plus end) and removal at the other (minus end).
During assembly the actin & tubulin monomers are bound to ATP and GTP respectively, which are progressively converted to ADP and GDP through the ATPase & GTPase activities of the actin and tubulin subunits
What is tread milling?
When the rate of filament assembly equals that of disassembly the filaments are said to be treadmilling: Constant turnover but no net growth
