Ch 17 Flashcards
types of protein filaments
- intermediate filaments (structure)
- microtubules (structure + transportation of cells i.e where motor proteins walk on)
- actin filaments (pull chromatids apart in cell division)
function of desmosome
connects two cells via adhesion
Structure of intermediate filament proteins
alpha helical
- exists as monomer, dimer, or staggered antiparallel tetramers
combines to create symmetric structure (max array of 8 tetramers)
4 major classes of intermediate filaments
- keratin (epithelial cells)
- vimentin (connective tissue, muscle, and glial cells)
- neurofilaments
- nuclear lamins
(1 - 3) are cytoplasmic
function of intermediate filaments
support and strengthen nuclear envolpe (or any plasma membrane)
function of plectin
links intermediate filaments to other networks (i.e other filaments such as actin filaments)
function of protein complexes in respect to filaments
bridge nucleus + cytoplasm on nuclear membrane
ex. KASH-domain (cytosol)
ex. SUN-domain (Nucleus)
what do KASH-domain proteins bind to?
microtubules, plectin, actin (microtubules bind via motor proteins)
what do SUN-domain proteins bind to?
nuclear lamina + chromatin
structure of micro tubules
13 parallel protofilaments (forms hollow tube)
tubulin dimers add to the plus end more than minus end
beta –> plus end
alpha –> minus end
polymerizes from nucleation sites on centrosome
Key property of microtubules
dynamic instability
–> grows when there are more dimers
–> shrinks when there are less dimers
controlled via GTP hydrolysis
Purpose of microtubules capping protein
captures microtubule to make it stable (therefore it won’t break down)
function of microtubules
guide the transport of organelles, vesicles, and macromolecules
help position organelles
What is Mitotic arrest
cells stop dividing (also caused when tubules stop growing)
–> drugs cause this to treat cancer growth
types of motor proteins
cytoplasmic denein –> moves towards minus end of microtubules (back towards nucleus)
kinesin –> moves in plus end
(away from nucleus)
How do motor proteins walk?
- one head gains ATP
- changes conformation (P is released)
- that head pulls “forward”
- binds to microtuble and other head gains ATP to repeat cycle
How are microtubules formed in a cilium / flagellum
9 + 2 array
9 –> microtubules on outer layer
2 –> microtubules in center
Relationship between dyneins + flagellum
dyneins cause flagellum to bend
Compare and contrast microtubules and actin filaments
Differences:
- Actin filaments are shorter than microtubules
- total length of actin filaments is longer than microtubules
- Actin supports movement + structure (ex. filpodia, microvili, contractile ring in cell division)
- Microtubules support structure
Similarities:
- both grow faster at their plus end (dynamic instability for microtubules, tread milling for actin)
- both composed of protein units
- both involved in motor protein movement (dyneins and kinesines move along microtubules, myosins move along actin)
How do actin filaments grow based on actin monomer concentration?
Concentration is high –> grow rapidly at both ends
concentration is middle –> tread milling (actin goes out at minus end + actin goes in at plus end at same rate)
What are the types of actin-binding proteins and their functions?
- nucleating proteins:
binds to minus end and stop degradation - monomer-sequestering protein
prevents polymerization - severing protein
hydrolyzes long actin filaments - bundling protein
used in creation of filopodia - cross-linking protein
- links actin in cell cortex to strengthen membrane
6.capping protein
- stops growth
- side-binding protein (tropomyosin)
- forms coils to block myosin and other proteins from binding to actin
How is actin used in cell crawling?
- actin polymerization protrudes lamellipodium (reach)
- attaches to surface by focal contacts that contain integrins (grab)
- myosin motor proteins slide along actin filament (pull)
Compare and contrast myosin 1 and myosin 2
Myosin 1
- moves towards plus end (to plasma membrane)
- associated with movement of vessicles
Myosin 2
- associated with movements of muscles (slides two actin filaments together to contract)
- often forms bipolar (actin filament binding at both ends) filaments
Explain the structural differences between lamellipodia and filopodia and their associations with the two actin filament nucleating proteins: formin and the actin-related protein (ARP) complex
Lamellipodia (sheet feet) –> contains more ARP complex to form mesh-like structures
filopodia (spike feet) –>
contains more formin to creaate long structures
What do the Rho-family GTPases do?
promotes formation of rapid assembly of long unbranched actin filaments (Rho),
lamellipodia (Rac),
and filopodia (Cdc42)
Describe the structure and movement of a sacromere
Structure:
- Z disc: binds sacromeres together
- actin filaments: attaches to Z disc at plus end + myosin filament at minus end
- myosin filament: at centre of sarcomere
Function:
contraction: mysosin pulls on actin filaments –> shortens sarcomere
relaxation: myosin releases actin filaments
Describe the ATP-dependent cycle of myosin 2 (how it walks across actin filaments)
- Attached
- myosin and actin are binded together (rigor configuration) - Released
- ATP binds to head of myosin that causes conformation changes –> myosin lets go of actin b/c reduced affinity - Cocked
- head of myosin tightly clamps around ATP molecule
- ATP molecule hydrolyzes into ADP and P (but still binded to myosin)
- myosin head moves 0.5 mm in direction of minus end of actin filament - Rebending + Power stroke
- ADP + P are released when myosin head weakly binds to new actin filament site –> myosin can now bind tightly to actin filament
Describe the mechanics of skeletal muscle contraction
- triggered by release of Ca2+
- Ca2+ release channel on Sarcoplasmic Reticulum is connected to voltage gated Ca 2+ channel
- When T-Tubule membrane is activated by an action potential: voltage gated Ca2+ channels open and also causes the Ca2+ release channel to open
- both lumen of T-tuble and sarcoplasmic reticulum release ca2+ into cytosol
–> creates myofibril contraction - controlled by tropomyosin + troponin complex
tropomyosin: string that blocks myosin 2 from binding (prevents premature contraction)
troponin: protein complex with Ca2+ sensnsitive protein
both proteins ensure that contraction occurs only when action potential is released
