The cytoskeleton Flashcards
what is the function of a skeleton?
function- allows the cell to keep its shape and modifies the shape due a response to environmental cues. Also controls intracellular movement of organelles
what are the general features of a cytoskeleton?
The cytoskeleton is a complex network made of 3 different polymers:
-microtubules
-intermediate filaments
-actin filaments.
What is the function of the polymer microtubules?
microtubules:
-organelle positioning
-intracellular transport
what is the function of the polymer intermediate filaments
intermediate filaments:
-mechanical strength
what is the function of actin filaments?
actin filaments:
-cell shape
-organelle shape
-cell migration
definition of accessory proteins
accessory proteins- assist in the function of other proteins
what do accessory proteins regulate?
accessory proteins regulate:
-site and rate of filament formation
-polymerisation/depolymerisation
-function
what is the structure and function of microfilaments/actin filaments?
Structure:
-helical polymers made of ACTIN
-flexible, organised into 2D networks and 3D gels
Function:
-cell shape
-organelle shape
-cell migration
what is the structure and function of intermediate filaments?
structure:
-heterogenous group of filamentous proteins (different types of proteins that forms filaments)
-rope like structure
function:
-gives mechanical strength to the cell
what is the structure and function of microtubules?
structure:
-hollow tubes made of TUBULIN
-rigid, long straight
function:
-organelle positioning
-intracellular transport
-cell movement
what is the structure of Actin filaments?
Actin filaments:
-twisted chains of monomers of the protein actin (G-actin) this chaoin constitutes the filamentous form of F-actin
-thinnest class of cytoskeleton filaments
-presents structural polarity
-associated with a large number of actin binding proteins
How are F-actin filaments formed?
F-actin can grow by addition of actin monomers (G-actin) at either end
what is the length o the filament determined by?
The length of the filament is determined by:
-concentration of G-actin
-presence of Actin Binding proteins
What are G-actin levels controlled by?
G-actin levels are controlled mainly by 2 ABPs:
-Profillin- facilitates actin polymerization
-Thymosin b4- prevents the addition of actin monomers to F-actin
What is the role of Actin Bundling proteins and Cross-linking proteins?
Actin Bundling Proteins- Keeps F-actin in parallel bundles (as the microvilli observed in epithelial cells)
Cross linking proteins- maintains F-actin in a gel like meshwork
What is the role of F-actin severing proteins and Motor proteins (Myosin)?
F-actin severing proteins:
-break F-actin into smaller filaments
Motor proteins (Myosin):
-transport of vesicles and/or organelles through actin filaments
Describe the structure and function of skeletal muscle?
structure:
-arranged in a para-crystalline array integrated with different ABPs
function- interaction with myosin motors allow muscles to contract
describe the structure of non muscle cells
structure:
-cell cortex: forms thin sheath beneath the plasma membrane
-associated with myosin to form a purse string ring.
explain cell migration in the actin filaments
-the cell pushes out protrustions at its front.
-actin polymerisation
-these protrustions adhere to the surface
-integrins (link the actin filaments to the extracellular matrix)
describe the structure of intermediate filaments (IF) ?
intermediate filaments:
-toughest of the cytoskeleton filaments
-ropelike with many long strands twisted together
-intermediate size (8-12nm)
-forms a network
what is each unit of immediate filaments made of?
each unit is made of:
-N-terminal globular head
-C-terminal globular tail
-Central elongated rod-like domain
What are 2 types of intermediate filaments?
1) Cytoplasmic
2) nuclear
what does a nuclear intermediate filament form?
nuclear intermediate filaments:
-nucleur lamins in all nucleated cells
what do cytoplasmic intermediate filaments form?
cytoplasmic intermediate filaments form:
-keratins in epithelia
-vimentin and vimentin-related in connective tissue, muscle cells and neuroglial cells
-neurofilaments in nerve cells
explain the role of intermediate filaments binding proteins (IFBP)
IFBP stabilizes and reinforces IF into 3D networks
list examples of IFBP
Examples IFBP:
-Fillagrin:
binds keratin filaments into bundles
-Synamin and Plectin:
binds desmin and vimentin
-link IF to the other cytoskeleton compounds
Plakins:
what is the function of the IF in the cytoplasm?
IF- tensile strength: this enables the cell to withstand mechanical stress so they can stretch
what are the functions of the intermediate filaments in the nucleus?
functions of intermediate filaments in the nucleus:
-present in all nucleated eukaryotic cells
-forms mesh rather than rope-like structure
-line in the inner face of nuclear envelope allows it to strengthen and provide attachment sites for chromatin
-disassemble and reform at each cell division as nuclear envelope
what is the structure of microtubules?
structure of microtubules:
-hollow tubes made up of the protein tubulin
-relatively stiff (25nm)
-each filament is polarised
-assemble/disassemble in response to the cells needs
definition of microtubule organising centre (MTOC)
MTOC- specialised protein complexes from where the assembly of tubulin starts
what are the functions of microtubules?
INTRACELLULAR TRANSPORT:
-act like railway tracks on which molecular motors run
-different motors for different cargoes
-directionality of filaments is vital
ORGANISES POSITION OF ORGANELLES:
-provides polarisation of cells
-directionality of filaments is vital
