Chapter 12 Flashcards
(27 cards)
What are the three types of protein filaments in the cytoskeleton?
Actin filaments- determines cell shape, provide structural support and form cell projections and cel motility
Intermediate filaments- provide mechanical strength to cells, maintain tissue organization, mitigating impact of external forces on cell
Microtubules- rigid hollow rods that determine cell shape and are involved in cell movements (intracellular transport, positioning of membrane vesicles and organelles, separation of chromosomes, and beating of cilia and flagella)
What is the structure of actin filaments?
Actin is the predominant cytoskeletal protein of cells
Filamentous (F) actin- thin flexible filaments approx 7 nm in diameter and up to several micrometers length
Consist of head to tail arrangement of actin monomers (Globular (G) actin)
F actin can assemble in vitro but it is tightly controlled in Vivo by other proteins
Actin polymerization is reversible
Slide 4 and 5
What is the polarity of actin filaments?
Polarity is not a charge, it means they’re different at each end Pointed end (-end)- slow monomer addition Barbed end (+end)- rapid monomer addition Slide 5
What is ATP Actin and ADP actin?
What is treadmilling?
ATP Actin- associates with filaments more readily than ADP Actin
ADP Actin- dissociates from filaments more readily than ATP-Actin
Treadmilling- Occurs IN VITRO at equilibrium between rate of addition and removal of monomers
Slide 7 and 8
What is the rate limiting step?
What is it catalyzed by?
Initial polymerization of 3 Actin molecules
Catalyzed by formin
can occur anywhere in cell required
Slide 9-10
What are the two major forms of higher order Actin filament organization?
- Actin networks- actin filaments are cross linked in orthogonal arrays that form 3D meshworks (cytoskeletal framework underlying plasma membranes)
- Actin bundles- actin filaments are cross linked into closely packed arrays
What determines cell shape in terms of red blood cells and plasma proteins?
What is glycophorin?
Association of the red blood cell cortical cytoskeleton with the plasma membrane proteins determines cell shape
Glycophorin is associated with actin cytoskeleton network immediately underlying plasma membrane
Spectrin and actin firm the cortical cytoskeleton together
Slide 12
What are microvilli?
Finger like extensions of the plasma membrane that are particularly abundant on the surfaces of cells involved in absorption
Ex: epithelial cells lining intestine
Slide 13
What are Actin bundling proteins and actin network proteins?
Actin bundling proteins- small rigid proteins that force the cross linked actin filaments to align closely with one another in bundles
Alpha actinin- in contractile bundles
Fimbrin- in non contractile bundles
Actin network proteins- have 2 flexible arms that interact with separate actin filaments
Slide 14
What are stress fibers?
Bundles of contractile actin filaments in many cell types allows cell to exert force against the substratum through cell-extracellular matrix junctions
Slide 15
What are the 3 things required for cell movement or extension of long cellular processes?
- Actin cytoskeleton growth and branching atleasinf edge
- Dissociation of focal adhesions at trailing edge and formation of new focal adhesions at leading edge
- Actin cytoskeleton contraction at trailing edge
Slide 17
What is myosin?
What is a molecular motor?
Myosin- a protein that interacts with actin and acts as a molecular motor
A molecular motor is a protein that converts chemical energy in the form of ATP to mechanical energy, thus generating force and movement
Slide 19-20
How does a cell pull itself forward using Actin filament contraction?
Actin filament contraction in conjunction with extension of projections at leading edge through action polymerization/branching, and retraction of trailing edge through Actin depolymerization, allows the cell to pull itself forward
Uses anchoring if actin filaments at focal adhesions
Slide 21
What is the contractile ring in cytokinesis (division of cell into two cells)?
It is a structure of actin and myosin that forms beneath the plasma membrane during mitosis and mediated cytokinesis
Slide 22
What is the structure of intermediate filaments?
Does it have polarity?
Central alpha helical rod with greater variability in head and tail domains
No polarity in IFs!!
More stable than actin filaments or microtubules
Do not exhibit dynamic behaviour
Slide 26
What are plankins and plectin in intermediate filaments?
Plakin- family of proteins that bind intermediate filaments and link them to other cellular structures like cadherins, desmoglein and desmocollin of the desmosome
Plectin- type of plakin thag links IFs to integrins of hemidesmosome
Slide 29
What is tubulin?
Protein that polymerizes to form microtubules
One alpha and one beta Isoform combine to form a tubulin dimer
Tubulin dimers polymerize to form microtubules consisting of 13 linear protofilaments
What is the structure of microtubules?
Alpha tubulin faces plus end (fast growing) and beta tubulin faces minus end (non growing)
Microtubules have polarity!!
Slide 36 and 37
What is dynamic instability in microtubules?
Behaviour in which individual microtubules alternate between cycles of growth and shrinkage at the plus end
Dependant on rate of GTP hydrolysis at plus end of microtubule, and free pool of GTP bound tubulin dimers
Slide 38
What are the drugs colchicine and Colcemid used for?
What about vincristine and vinblastine?
Colchicine and colcemid are experimental drugs that bind tubulin and inhibit microtubule polymerization
Slide 42
Vincristine and vinblastine are used in cancer chemotherapy that inhibit microtubule polymerization and thereby cell division
Slide 40
What is the centrosome?
What are centrioles?
Microtubule organizing center in animal cells
Anchoring point of minus end of most microtubules
Initiated microtubule growth which grow out plus end
Slide 41
Centrioles are complex structures consisting of 9 triplet of microtubules in a ring structure
Slide 43
What are the 2 microtubule motor proteins?
Kinesins- motor proteins that move along microtubules both towards the plus and minus end depending on cell involved
Dyneins- motor proteins that move along microtubules only toward the minus end
Head region and tail region of each
Slide 45 and 46
What is the axoneme and basal body?
Axoneme- fundamental structural unit of organization of both cilia and flagella
Composed of microtubules and their associated proteins
Basal body- structure similar to a centriole that initiates growth of axonemal microtubules and anchors cilia and flagella to the rest of cell
Minus end of microtubules in cilia and flagella are anchored within basal bodies
How are the microtubules in cilia and flagella moved?
The movement results from the sliding of outer microtubule doublers relative to one another, powered by the motor activity of the axonemal dyneins
Slide 53
