Cytoskeleton Flashcards
Which secretory pathway doesn’t need a signal? What types of stuff gets transported on this pathway?
Constitutive secretory pathway. Add receptors to plasma membrane / secreting proteins without special features
Which secretory pathway runs through a signal cascade? What goes through it?
regulated secretory pathway. Sends out secretory proteins (have signals on them).
What signal marker diverts proteins to lysosomes?
Mannose 6-phosphate.
Do receptors go to lysosomes too? check in book
What is another word for actin filaments?
microfilaments
How many strands to actin filaments have? What are the strands?
Two strands. Helical polymers of the protein actin.
What important thing does an actin monomer have in a central cleft?
ATP or ADP
What designates the minus and plus end of an actin filament?
The orientation of subunits. They all have the same orientation
What protein causes actin to pack tightly?
fimbrin. Forms parallel bundle (orientation of all filaments is the same in terms of + and -)
Why does fimbrin packing actin tightly matter?
Tight packing prevents myosin II from entering bundle
What protein loosens up actin?
a-actinin. Forms contractile bundle (orientation of actin filaments is opposite in terms of + and -)
If there is no actin at all, how fast will it form compared to growing pre-existing actin?
Slower (lag phase)
What is it called when actin filaments aren’t growing or contracting?
equilibrium phase, steady state. Happens at Cc (critical concentration)
What needs to happen for actin filaments to be elongated?
Subunits have to be above critical concentration
What is treadmilling?
Subunits are getting removed at - end
Subunits are getting added at + end
Both happens at the same rate
At what concentration of filaments does treadmilling happen?
Intermediate concentration
What types of subunits do actin filaments contain?
T form (soluble)
D form
T subunits are at their critical concentration
D subunits are at their critical concentration
Is there the same number of subunits?
No. Cc of T requires less subunits
Cc of D requires more subunits
Treadmilling happens when you’re both above the critical concentration of T and below the critical concentration of D
Why? (Read book on this)
Why must proteins released to extracellular space need to be soluble?
Where do these proteins come from? How are they transported?
Soluble because that way they can get through membrane
Come from trans golgi, transported in lipids which become part of plasma membrane.
Which pathway are neurotransmitters exocytosized through? Why?
Regulated secretory pathway.
They need to wait by the plasma membrane in secretory vesicles
Which pathway are most membrane lipids and membrane proteins added through?
Constitutive secretory pathway
Lipids come from the vesicles themselves, membrane proteins attached to vesicles during travel
Where in relation to the ER / cytoplasm are the cisternae of the trans golgi network?
Cis golgi network?
Trans is closer to the cytoplasm
Cis is by the ER
What makes up a single intermediate filament coiled-coil dimer?
Two dimers wrapped around each other
antiparallel (n-terminus next to c-terminus)
What makes up a single intermediate filament? How do they grow?
Two coiled-coil dimers form a tetramer by lining up (c-terminus next to c-terminus, staggered)
8 tetramers line up in parallel. 32 individual a-helical coilds per filament.
To grow, another circular set of 8 filaments adds on to the end
Where can a dense network of intermediate filaments be found? Why? What are they called?
Nuclear lamina (called nuclear lamins).
Anchorage site for chromosomes / nuclear pores
What is keratin? Where do you see it? What’s it made of?
Type of intermediate filament made up of acidic + basic subunits in each coiled-coil dimer
See it in hair, nails, etc
What is the process of actin forming its initial aggregate that can then grow called?
nucleation
What are the T and D forms of actin subunits?
T form = ATP inside
D form = ADP inside
Is it harder to separate a D subunit or T subunit of actin?
D subunit. Energy of hydrolysis gets stored in polymer when ATP>ADP
What form are soluble actin subunits in?
Polymers?
Generally T form
Polymers a mixture of T and D, but more D the longer they’ve existed
What protein causes closer packing? What is the result of that?
What protein causes looser packing? What is the result?
Closer packing: fimbrin. This close packing excludes myosin, so parallel actin filaments with fimbrin can’t contract
Looser packing: a-actinin. Allows binding of myosin, sow formation of antiparallel contractile actin bundles.
What kinds of things do actin accessory proteins regulate?
Change formation ability (nucleation)
Speed actin forms (adding to + end)
Size of filament (e.g. capping protein)
Stability (more or less rigid)
Number of filaments
Geometry (bundling, crosslinking like in neuron growth, attachment to plasma membrane)
What does a myosin II motor protein look like?
What are the functions of each component?
heavy chain: Neck with two heads (force-generating machinery)
heavy chain: Long coiled-coil (heavy-chain dimerization)
light chains
C terminus
What are multiple myosin filaments together called?
What do they look like?
Myosin II bipolar thick filament
Myosin tails making a fiber, heads on the outside
Fiber has two parts, with heads on each side, pointed towards each other:
o== ==o
Which direction does myosin walk along actin? How?
How does this turn into myosin moving muscle?
Myosin head hydrolizes ATP
Uses that energy to walk towards + side of actin
Bipolar thick filament moves oppositely oriented actin filaments towards each other
How can small bipolar myosin filaments quickly be formed?
What is the purpose of this?
Inactive myosin: light chains dephosphorylated
Active myosin: light chains phosphorylated
Myosin activation causes head to start binding actin, tail to start forming bipolar filaments
Purpose: Control non-muscle contractile bundles. Give mechanical support to cells
What is the purpose of Myosin V? (two-headed, large step size)
Transport stuff along actin by walking along filaments towards + end
What direction do intermediate filament monomers assemble?
Parallel
How rigid is a microtubule compared to other cytoskeleton components?
More rigid than actin
What are the linear strings of tubulin that make up microtubules called?
What are they composed of?
How many are there?
How are they organized?
Protofilaments
…alpha tubulin - beta tubulin - alpha tubulin…
13 make up a microtubule
They connect with each other laterally to make a circle
What’s the inside of a microtubule called?
microtubule lumen
Is GTP more tightly bound in a- or B- tubulin?
Why does this matter?
alpha tubulin
GTP can never be hydrolized to GDP in a-tubulin, only in B-tubulin
Why are microtubules so stiff?
(same reason they only add / get removed at the ends)
Protofilaments aren’t right next to each other, they’re staggered a bit
Because of this, each subunit has multiple connections with other subunits
This makes for very high energy in the middle of microtubules
Which direction on a microtubule, +-, do dyneins travel?
Towards the - end
How fast does GTP hydrolysis occur in free B-tubulin vs B-tubulin in microtubules?
If GTP is hydrolyzed to GDP, what happens to B-tubulin?
Slow in free tubulin
Fast in microtubule
Tubulin relaxes into curved conformation, allowing catastrophe
What complexes do microtubules grow from?
What end of microtubule goes away from centrosome?
y-tubulin ring complexes of centrosome
+ end goes out
What is the material in the MTOC called? What is another name for it?
Material = pericentriolar material
MTOC = centrosome in animal cells (one per G1)
What is the actual function of centrioles?
Organize centrosome matrix
Become basal body of cytoskeletal apparatus in cilium / flagella
What are melanocytes? Why are they important?
Pigment granules, shows that kinesins/dyneins can be controlled by hormonal changes
Less cAMP = inactivated kinesin, dynein drags granules towards center (change fish color)
More cAMP = kinesins (both) activated, granules spread out (kinesins stronger)
