Exam 3 Oakes Cytoskeleton I Flashcards by Sharon Hull

Explain the four functions of the cytoskeleton

Functions of the cytoskeleton:

Gives cells shape
Critical component of cell division
Structure and Polarity
Cargo Transport

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_______ 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

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List the four main components of the cytoskeleton

Main components of the cytoskeleton:

Actin

Microtubules

Intermediate Filaments (IFs)

Septins

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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

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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

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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

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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

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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

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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

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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

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______________ regulate spatial distribution and dynamics of the cytoskeleton

Assesory proteins regulate spatial distribution and dynamics of the cytoskeleton

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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

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What kind of structure is tubulin? What kind of dimer, trimer, etc.

Tubulin acts as an alpha beta dimer

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keratin is made up of ____ regions

Keratin is made up of coil coil regions

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Important structural component of septins

Septins are palindromic

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_______ 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)

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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

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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