Exam 3 Oakes Cytoskeleton I Flashcards
Explain the four functions of the cytoskeleton
Functions of the cytoskeleton:
- Gives cells shape
- Critical component of cell division
- Structure and Polarity
- Cargo Transport
_______ act as highways within the cells to transport material to specific points in the cell
Microtubules acts as highways to transport materials to specific points in the cell
List the four main components of the cytoskeleton
Main components of the cytoskeleton:
Actin
Microtubules
Intermediate Filaments (IFs)
Septins
Explain the basics of actin (structure and function)
Actin is polarized, it has a pointed and barbed end
Actin helps with: giving cell shapes, supports plasma membrane, helps with contraction
Explain the basic structure and function of microtubules
Microtubules are polarized with a + and - end
They help with positioning organelles, intracellular transport tracks
think highway
Explain the basic structure and funciton of IFs
IFs are a family of proteins that are not polarized
They provide mechanical strength (protects the cell from damage)
Think of IFs as protective padding
Explain the basic structure and function of septins
Septins have 13 different isoforms
Made of up oligomers that have palindromic repeats
Function: support PM, cillia, flagella
Each type of cytoskeletal filament is constructed from ______
Small soluble subunits assemble into large filamentous polymerrs
FINITE resources
Each type of cytoskeletal filament is constructure from smaller protein subunits: alpha coiled coils, actins, and tubulins
Of the four types of cytoskeletal parts, which ones are polarized and which ones are single proteins?
Actin and microtubules are polarized
Actin and microtubules are also single proteins
What type of bonds are important for the fast assembly and degradation of cytoskeltal parts?
WEAK COVALENT interactions are important for fast assembly and disassembly
______________ regulate spatial distribution and dynamics of the cytoskeleton
Assesory proteins regulate spatial distribution and dynamics of the cytoskeleton
Explain the specific structure of actin
does it have a binding pocket?
Actin is called “g” actin for the fact that it is a globular protein, it has a binding pocket for atp
What kind of structure is tubulin? What kind of dimer, trimer, etc.
Tubulin acts as an alpha beta dimer
keratin is made up of ____ regions
Keratin is made up of coil coil regions
Important structural component of septins
Septins are palindromic
_______ provide stability
Single protofilament vs multiple protofilament
Bundled Filaments provide stability
Single protofilament: thermally unstable
Multiple protofilament: thermally stable
(this applies to actin as well)
Define persistance length
Rank the following from highest to lowest persistance length: actin, microtubules, IFs
Persistance Length: minimum filament length at which random thermal fluctuations are likely to cause it to bend (example, DNA is really floppy and has a tiny PL, where as microtubules are like steel and have long PL)
Highest to lowest PL:
Microtubules > Actin > IFs
What governs cytoskeletal behavior?
Accessory proteins and adaptor proteins govern cytoskeletal behavior
Which of the following is NOT a process regulated by the cytoskeleton?
Cell polarity
Cell migration
Cell wall synthesis
ATP production
Cell Division
ATP production is not regulated by cytoskelton
cell migration, polarity, division, and wall synthesis are
_____ drives migration and contractility
Explain these structures:
shape
pitch
location
How does it grow
ACTIN drives migration and contractility
Actin filaments are helical polymers of actin
Highly concentrated in the cortex (just beneath the PM)
37 nm half pitch
Actin adds to the plus end
Draw the graph explaning the nucleation and elongation of actin
What is the rate limiting step
Rate limiting step is formation of the trimer (nucleation phase)
Explain k on and k off
What is the critical concentration?
What is kd?
Rate of addition of monomers is given by k on and k off (M ^-1 sec^-1). Its a rate constant
Critical concentration: kon * C = k off
(critical concentration is the concentration when you are just as likely to add a monomer as you are to lose one)
Also Cc = koff / kon = kd
(dissociation constant)
_______ allows for addition and substraction of monomers at different rates in the filament
Hydrolysis allows for addition and subtraction of monomers at different rates in the filament
Explain ATP cap and treadmilling
ATP is likely to be added at the plus end
It gets hydrolyzed and then ADP falls off the minus end of the actin filament
Plus end addition is fast whereas minus end addition is super slow
Treadmilling is when the rate of addition equals the rate of falling off (looks like the actin is moving)
How many isoforms of actin are there?
There are three differrent isoforms of actin
alpha, beta, and gamma
alpha is tissue specific
beta and gamma are ubiquitous
Explain what profilin and thymosin do to regulate polymerization
Both profilin and thymosin grab onto individual actin monomers
Profilin speeds up polymerization (increases elongation)
Thymosin actually inhibits polymerization and prevents the monomer from adding on
Explain what formin does
Formin nucleates assembly and remains associated with the growing plus end
It is good at making long straight parallel actin filaments
Explain what Arp 2/3 complex does
Arp 2/3 nucleates assembly to form a web and stays associated with the minus end
Binds to side and creates branches
Explain the connection between lysteria and arp/23
Lysteria hijacks the branching network to propel it around the cell and into neighboring cells
formins rapidly elongate _______
formins rapidly elongate actin filaments
Explain the following actin crosslinkers:
fimbrin
alpha actinin
Actin crosslinkers:
fimbrin forms parallel bundles
alpha-actinin forms anti-parallel bundles
Explain the function of the following proteins:
cofilin
topomodulin
capping protein
tropomyosin
Gelsolin
Cofilin: binds ADP actin filaments, accelerates diassembly
Tropomodulin: prevents assembly at minus end
Capping protein: prevents assembly and disassembly at plus end
Tropomyosin: stabilizes filament
Gelsolin: severs filaments and binds to the plus end
Explain the affects of these drugs on actin:
Lantrunculin
Cytochalasin B
Phalloidin
Lantrunculin: prevents actin from polymerizing by binding to actin subunits
Cytochalasin B: depolymerizes filaments by capping subunits at the plus end, preventing growth
Phalloidin: stabilizes by binding along filaments
So, bith lantrunculin and cytochalasin cause depolymerization of filaments, and phalloidin stabilizes filaments
The power stroke of myosin is triggered by…?
Power stroke is triggered by release of Pi
Explain the structure of myosin II
It has ___ heads, and ____ light chains
The light chains are where _____ happens
Myosin II also has a coil-coil of two alpha helices that is ___ in length
Myosin II structure:
Two heads, two light chains
Light chains are where the phosphorylation event occurs
Myosin II has a coil-coil region of alpha helices that is 150 nm in length
Fill in the blank with actin and myosin
______ provides the structure
_______ generates the force
Actin provides the structure
Myosin generates the force
Explain how hydrolysis drives myosin conformational change
Myosin generates force through ATP hydrolysis. As the ATP is converted to ADP and Pi, the Pi is released, the head region of myosin II protein undergoes conformational change. Since the myosin is bound to actin when this happens, it generates force.
Note: when the myosin II head is bound tightly to actin with no ATP, this is the “rigor” state
Explain the different myosin II isoforms: nonmuscle, smooth muscle, and skeletal muscle when it comes to the following:
motor speed
force
thick filament geometry
thick filament length
Nonmuscle: slow, weakest force, bipolar geometry, small length
Smooth muscle: medium speed, medium force, SIDE POLAR, medium length
Skeletal muscle: fastest motor speed, largest force, bipolar geometry, longest length
“skeletal muscle is faster with more force and has more heads”
________ are the basic contractile unit
SARCOMERES are the basic contractile unit
Sarcomeres are measured from Z line to Z line aka
Explain how sarcomeres contract
Sarcomeres start to contract when there is an increasing amount of interaction between myosin heads and actin
Actin begins to overlap with myosin, number of interacting myosin heads remains constant
Actin filaments start to overlap with each other: interfering with the process.. this is NON OPTIMAL
Within a sarcomere explain the roles of titin, Z discs and myosin
Myosin pulls the Z discs together
Titin acts like a spring
What ion regulates contraction?
Calcium
Calcium gets released into the cytoplasm, binds to TROPONIN, which then moves out of the way so myosin can interact with actin
_______ drives migration
______ drives contractility
ACTIN cytoskeleton drives migration and contractility
