Chapter 17: The Cytoskeleton Part II Flashcards
1
Q
Actin
A
- actin filament -> polymers of actin
- mnost abundant protein in nearly all cell types
-maintain cell shape and movements that involve cell outer membtane - actin filaments interact with actin-binding proteins that enable filaments to serve various functions
- has movement driven with motor proteins (like microtubules!!)
2
Q
cytoskeleton filaments
A
- constructed from smaller protein subunits
- smaller soluble subunits & large filamentous polymer
-dynamic and adaptable - formation of protein filaments from smaller protein subunits allows regulated filament assembly and dissassembly to reshape to cytoskeleton
3
Q
Actin filaments
A
- thin, flexible protein with structurally distinct ends
- two stranded helix with twists, twists of identical globular monomers, they “face” same direction
-lateral interaction prevent separation - shorter than microtubules
- grow by addition of monomers on either end (plus side faster)
- similar to microtubules: such as polarity with plus and minus end
4
Q
Actin polymerization
A
- actin monomers in cytosol carry ATP
- ATP hydrolyzed to ADP soon after assembly into growing filament
- ADP molecules remain trapped within actin filament, unable to exchange with ATP until actin monomer carries them dissociates from filament
5
Q
Actin “treadmilling”
A
- rate of monomer addition = rate of monomer loss (remains one length)
- causes move through of actin from plus end to minus end
- if actin monomers added to plus end faster than ATP is hydrolyzed, then plus end grows
- if ATP hydrolyzed faster than monomers added, the minus end loses (ADP-actin destabilizes, loose structure)
6
Q
Microtuble dynamic instability
A
- switching between polymerization and depolymerization
- undergo rapid remodeling
- crucial to function (division)
-stems from intrinsic capacity of tubulin dimers to hydrolyze GTP
7
Q
Growing microtubule
A
- grow since bound to GTP
- GTP-tubulin combo hydrolyzes to GDP after dimer is added
- rapid polymerization, tubulin dimers bind faster than GTP hydrolyze
- this makes end completely GTP-tubulin dimers, creates GTP cap(packs efficiently and grows)
8
Q
shrinking microtubule
A
- hydroylzed GTP to GDP + phosphate
- protofilaments composed of GDP tubulin pack loosely, favoring dissassembly
- once depolymerization starts, it continues
- dissasssembled GDP tubulin in cytoplasm (exchange bound GDP for GTP so they can be added to growing microtubule
9
Q
microtubule building-
A
- microtubules grow when bound to GTP, but when GTP is hydrolyzed to GDP microtubules shrink
10
Q
nucleation
A
- occurs in actin and microtubules
- the process by which atoms or molecules come together to form a new phase or structure.
- rate limiting step in polymerization
-helical polymer stabilized by multiple contacts between adjacent subunits - (in actin, two actin molecules bind realtively weakly to each other, third actin creates trimer to make entire group more stable)
- further monomer addition can take place for trimer, which therefore acts as nucleus for polymerization
- slow assembly from lag phase(can be reduced or abolished)
11
Q
Lag phase
A
- seen during polymerization
- when cells are adjusting to a new environment before starting exponential growth
- reduced or abolished entirely by adding premade nuclei, such as fragments of already polymerized microtubules or actin filaments
12
Q
Course of polymerization
A
- assembly of protein into a long helical polymer such as a cytoskeletal filament or bacterial flagellum
-lag phase(lower polymers and low time) - growth phase (increasing polymers over time)
- equilibrium phase (no net change, higher polymers and time)
13
Q
Lag phase
A
corresponds to time taken for nucleation
14
Q
growth phase
A
occurs as monomers add to exposed ends of growing filament, causing filament elongation
15
Q
equilibrium phase
A
steady phase, reached when growth of polymer due to monomer addition precisely balances the shrinkage of the polymer due to disassembly back to monomers
16
Q
Nucleatin of Actin
A
- involves ARP complex, Formins
- makes different types of actin filaments
- typically occurs in response to extracellular signals and is catalyzed by actin related proteins(ARP complex)nucleating at minus end, allowing rapid elongation at plus end
17
Q
Formin
A
- proteins
- actin elongation mediated by formins
- forma dimeric complex that can nucleate new actin filaments
- nucleates growth of straight, unbranched filaments that form parallel bundles and remain associated with rapidly growing plus end as it elongates
- maintains binding to one of the two actin subunits at the plus ends
- formins connect indirectly to plasma membrane
18
Q
ARP complex
A
- actin related proteins
- contrasts to formins
- nucleates and remains bound to minus end and form branched webs of actin
19
Q
Actin Cell Movement
A
- depends on polymerization and depolymerization of actin in response to signals
- actin nucleatin influences the type of protrusions formed at leading and trailing edge (involved cell crawling)
20
Q
Cell crawling
A
- cell sends out protrusions at its front/leading edge
- thes protrusions adhere to the surface over which cell is crawling
- rest of cell drags itself forward by traction on points of anchorage
21
Q
ARP promotion
A
- promotes formation of branched actin filaments in lamellipodia (filaments produce side branches; web undergoes addition at leading edge and disassembly further back, pushes lamillipodium forward)
22
Q
Actin-binding proteins
A
- bind to actin monomers in cytoplasm (regulate when/where actin filaments form and grow; ARP and formins promote actin polymeriztion)
- controlled by extracelular signal molecules (act through cell surface receptor proteins, activate signal pathways; coverage on group relaed monomer GTPases)
23
Q
Cell motility
A
-cell polymerization here involes activation of different Rho members at cell opposite ends that give motility, allows movement in particular direction
involves cell signaling(changes in actin cytoskeleton)
- have receptor proteins that act on intracellular targets (Rac, Rho)
24
Q
Rac and Rho
A
- GTP binding proteins involved in cell motility
- molecular swtiches: control intracellular processes by cylcing between active GTP-bound state and inactive GDP bound state
25
Q
Rho protein family
A
- alter organization of actin filaments
- one triggers bundling of actin filaments and activation of formin proteins (promotes filopodia formation)
- one activates nucleation promoting factors, stimulate ARP complexes that iduce lamellipodia formation
- one (MAJOR) bundles actin filaments with motor proteins to form contractile fibers
26
Q
Actin motor proteins
A
thymosin and myosin
27
Q
thymosin
A
bind and prevent addition to actin filaments until needed (contribute to regulation)
28
Q
myosin
A
in family or motor proteins that bind to and hydrolyze ATP; provides energy for actin filament to move forward toward plus end)
29
Q
various actin binding protein functions
A
actin bundling that holds parallel bundles together, cross-links together to support membrane, and severing proteins to create shorter lengths
30
Q
Muscle contraction
A
- triggered by sudden rise in cytosolic Ca2+ (released to ion channels in sarcoplasmic reticulum membrane; often relays messages from cell exterior to cell interior
- small, bipolar myosin II filament can slide two actin filaments of opposite orientation past each other(generates strong contractile force!)
- myosin II head group walks toward the plus end of the actin filament with which it interacts; multiple myosin molecules required to generate movement
31
Q
muscle myosin in myosin II subfamily
A
-muscle contraction depends on these interacting filaments of actin and myosin
- has dimer proteins: two globular ATPase heads at one end and single coiled coil tail at other
- clusters of myosin II bind through tail to form bipolar myosin filament(heads project outwards)
32
Q
structures of muscle contraction
A
- skeletal muscle fibers formed by fusion of many separate cells(bulk made of myofibrils)
33
Q
myofibrils
A
- contractile elements of muscle cell, actin filaments and myosin II filaments arranged in organized structure call sacromeres!
- myosin II in middle, actin on outer edges extending inward
34
Q
sacromere
A
- consits of ordered array of parallel and partly overlapping thin(actin, light bands) and thick filaments(myosin, dark bands)
- attachment of each thin filament occurs at Z-disc/line (no myosin)
35
Q
Detailed description of rise in Ca2+ for muscle contraction
A
- activates molecular switch of accesory proteins
- includes tropomyosin and toponin to control skeletal muscle contraction
- in resting muscle troponin I pulls tropomyosin out of the helix therby blocking myosin binding site on actin
- binding of Ca2+ to troponin C forces conformational change diriving the tropomyosin complex deep with the actin helix exposing the myosin binding site on actin
- single passed rapidly
36
Q
Mutant keratin
A
- skin more prone to blistering
- rare human genetic disease, epidermolysis bullosa simplex
- keratin genes intefere with formation of keratin filaments in epidermis
37
Q
Anti-mitotic drugs
A
- can control caner that target mitotic spindle
- some drugs destabilize microtubules by interfering with polymerization of tubulin dimers
- cause inappropriate proliferation tumor cells to die
- at expense of death of healthy tissue as well
38
Q
Ciliary dyenin
A
- left-right asymmetry caused by mutations in these
39
Q
neutrophils
A
- migrate out of blood into infected tissues when small molecules released by bacteria (engulf them when found)
