Cytoskeleton Flashcards
What is definition of cytoskeleton?
Skeleton of cell
What does the cytoskeleton provide for?
Shaping of cell
Intracellular movement of organelles
Cell movement
What are 3 different polymers that make up cytoskeleton?
Microtubules
Intermediate filaments
Actin filaments
Describe the structure of microfilament(actin filament)
Helical polymers made of actin
Flexible, organised into 2D networks +3D gels
Are most highly concentrated in cortex just beneath the plasma membrane
Twisted chain of units of protein actin, G actin
Chain constitutes filamentous form (F actin)
Prevents structural polarity
Associated with larger number of actin binding proteins (ABP)
There are 3 isoforms of G actin with different isoelectric point=> a actin found in mainly in muscle cells, B actin + gamma actin in non-muscle cells
Describe the structure of intermediate filament?
Heterogenous group of filamentous proteins
Rope like structure with many long strands twisted together + made up of different subunits
Toughest of cytoskeleton filaments
Intermediate size between actin + microtubules
Form network => throughout the cytoplasm, joining up to cell-cell junctions (desmosomes) + surrounding nucleus
Describe the structure of microtubules?
Hollow tubes made of protein Tubulin Rigid, long straight Thickest of the filaments Each filament is polarised It is dynamic structure => assemble + dissemble in response to cell needs
What is function of microfilament?
Cell shape
Organelle shape
Cell migration
What is function of intermediate filaments?
Mechanical strength=> resists high pressure
Give the shape of the cell
What is function of microtubules?
Organelle positioning
Intracellular transport=> facilitate the distribution of components through cell
What are 2 actin binding proteins that control G actin levels?
Profilin: facilitates actin polymerisation-> binding of monomers to filament therefore to extend filament. Having actin monomer bound to profilin helps the reaction
Thymosin B4: prevents addition of actin monomers to F actin. Thymosin B4 competes with profilin + binds to actin to form actin+thymosin complex=> cannot bind to actin filaments
What is function of cross-linking protein?
Maintains F actin in gel-like meshwork
What is function of actin bundling protein?
Form thicker bundle of actin
Keep F actin in parallel bundles
What is function of F actin severing protein?
Break F actin into smaller filaments
By severing them, there are more ends where actin can be depolymerised=> it accelerates the process
What is function of motor protein (myosin)?
Transport of vesicles and/or organelles through actin filaments
Examples of microtubules
Cilia in respiratory tract, sweeping mucus + debris from lungs
Flagella on spermatozoa
What are intermediate filaments binding proteins?
Mainly linker of IF structures
IFBP stabilise + reinforce IF into 3D structure
Give examples of IFBP
Fillagrin=> binds to keratin filaments into bundles
Synamim + Plectin => bind desmin + vimentin, link IF to other cytoskeleton compounds as well as to cell-cell contact structure (desmosomes)
Plakins => keep contract between desmosomes of epithelial cells
Actin polymerisation
ABP= actin binding proteins Actin filaments (F actin) can grow by addition of actin monomers (G actin) at either end Length of filament determined by: Concentration of G actin Presence of ABP
Intermediate filaments polymerisation
Each unit made of
N terminal globular head
C terminal globular tail
Central elongated rod-like domains
Units form stable dimers
Every 2 dimers form tetramer => bind to each other + twist to constitute rope-like filament
Microtubules polymerisation
Microtubule organising centre (MTOC) re specialised protein complexes from where assembly of tubulin unit starts
Centrosome is MTOC in most of cells=> contains gamma tubulin ring that initiates microtubule growth
Heterodimers of a +B tubulin constitute microtubule
It is polarised growth
