Scaffold of the Cell Flashcards
What are the3 major types of protein filament in the cytoskeleton?
- actin microfilaments
- tubulin microfilaments
- intermediate filaments
What are the roles of microtubules in cells?
- maintain cell shape
- swimming and surface movement of fluids
- formation of the mitotic spindle
- tracks for movement of vesicles organelles, proteins
What is tubulin?
-a dimer made out of α and beta tubulin subunits
What can each dimer of tubulin bind to?
2 GTP molecules
What gives tubulin polarity?
the GTP on beta tubulin being hydrolysed
How does the polymerisation of microtubulins occur?
- tubulin monomers from dimers
- the dimers polymerise into oligomers
- oligomers grow into linear protonfilaments and Mts
- MTS elongate reversibly by adding dimers. Dimers attach to both ends of Mts but preferably at + end
what is a MTOC?
microtubule organising centr
How are MTOCs form?
formed from enucleated microtubules
Describe the growth of MTs?
microtubules may grow steadily and then shrink rapidly by loss of tubulin dimers from the + end
What are the two classes of microtubule binding drugs?
tubulin dimer binding
tubulin polymer binding
What does the action of the dimer binding microtubule drugs tend to be?
inhibit polymerisation
What is an example of a polymer binding microtubule drug and what is its action?
- taxol
- favours polymerisation
What are MT binding drugs used as?
- anti-mitotic agents
- anti-cancer agents
What is taxol used to treat?
ovarian carcinomas and advanced breast carcinomas
What is vinblastine/viscristine?
-Hodgkin’s disease
-lymphocytic lymphoma
histiocytic lymphoma
-advanced testicular cancer
-advanced breast cancer
-Kaposi’s sarcoma
What are microtubule-associated proteins (MAPs)?
a family of proteins that bind to and stabilise microtubules
What is the function of MAPs?
- MAPs binding speeds up polymerisation, facilitates MT assembly and stabilises the microtubules
- the other end projects outing will bind to vesicles, actin or other MTs
What is MAP function regulated by phosphorylation?
phosphorylation
What are some features of microtubules?
- thickest of cytoskeletal filaments
- 2 tubulin isoforms: alpha and beta
- GTP dependant assembly
- long hollow cylinders made up of 13 protofilaments
- dynamically unstable
- attach to microtubule organising centres
- ovement of organelles and vsicles, cell division
What are the roles of actin filaments in cells?
- maintenance of cell shape
- cell movement of chemotaxis
- interaction of environment
- tracks for movement of vesicles, organelles, proteins etc
What are the actin filament locations in cells?
- microvilli
- adhesion belt
- cell cortex
- filopodia
- lamellipodium
- stress fibres
- contractile ring
What are the three types of actin?
α-actin
beta actin
gamma actin
What can a monomer of actin bind to?
one molecule of ATP or one molecule of ADP
How do the actin subunits arrange themselves?
the subunits are polar and assemble head to tail with one another
What are the stages of actin polymerisation in vitro?
- nucleation (lag phase) actin subunits form oligomers
- elongation (growth phase) actin filaments grow
- steady state (equilibrium phase) actin filament with subunits coming on and off
What drugs work on actin and how do they work?
Phalloidin (stabilises F-actin by locking adjacent subunits together which kills the cell)
Cytochalasin (binds the barbed end of F-actin and prevents polymerisation)
Latrunculin (binds to actin monomers and prevents them from being added onto filaments)
What does actin polymerisation provide?
a force for cell movement
How is actin arranged?
organised into many different patterns (2D and 3D patterns)
How many actin isoforms are there and where are they found?
6
4 in muscle
2 in cytoskeleton
What are the difference in mechanical properties of IFs, MFs and MTs?
- MTs are deformable but unable to withstand force
- actin filaments can withstand moderate force but are not easily deformed
- IF are able to withstand high forces and are highly deformable
What are some features of IFs?
-intermediate in size
-nuclear filaments-lamins
-others specific to cell type
mechanical stability-twisted coils
