Actin Polymerization and Muscle Contraction

<p>Pyrene fluorescence provides a quantitative measure of the amount of actin polymer formed. (D)</p> Signup and view all the answers

<p>Salt promotes the interaction between actin monomers, leading to filament formation. (A)</p> Signup and view all the answers

<p>ATP is hydrolyzed during actin polymerization, providing energy for filament growth. (C)</p> Signup and view all the answers

<p>ATP hydrolysis by myosin provides the energy for the movement of actin filaments along myosin. (C)</p> Signup and view all the answers

<p>Actin plays a similar role in both, providing a dynamic framework for movement. (A)</p> Signup and view all the answers

<p>The filament is undergoing rapid polymerization. (A)</p> Signup and view all the answers

<p>The subunit becomes more susceptible to depolymerization. (C)</p> Signup and view all the answers

<p>The concentration of ATP-bound G-actin monomers. (C)</p> Signup and view all the answers

<p>Hydrolysis destabilizes filaments by promoting subunit dissociation. (B)</p> Signup and view all the answers

<p>The minus end is associated with a lower concentration of ATP/GTP-bound subunits. (B)</p> Signup and view all the answers

<p>To regulate the rate of filament depolymerization by weakening inter-subunit bonds. (A)</p> Signup and view all the answers

<p>It opened up new avenues for understanding the molecular basis of muscle contraction. (B)</p> Signup and view all the answers

<p>Actin filaments undergo more rapid depolymerization than microtubule filaments. (A)</p> Signup and view all the answers

<p>The elongation rate is zero. (D)</p> Signup and view all the answers

<p>The concentration of free subunits at which the polymer is in equilibrium. (A)</p> Signup and view all the answers

<p>The polymer grows. (B)</p> Signup and view all the answers

<p>Elongation rate = kon * subunit - koff (C)</p> Signup and view all the answers

<p>The polarity of actin allows for bidirectional growth. (A)</p> Signup and view all the answers

<p>A state where the rate of subunit addition is equal to the rate of subunit dissociation. (D)</p> Signup and view all the answers

<p>Cc = koff / kon (A)</p> Signup and view all the answers

<p>The elongation rate is negative and proportional to the difference between the subunit concentration and the critical concentration. (B)</p> Signup and view all the answers

<p>dn/dt is zero. (B)</p> Signup and view all the answers

<p>A subunit that is not bound to the polymer. (D)</p> Signup and view all the answers

<p>The concentration of actin monomers at which filament polymerization and depolymerization are balanced. (D)</p> Signup and view all the answers

<p>If the G-actin concentration is between the critical concentrations for the plus and minus ends, only the plus end will grow. (A)</p> Signup and view all the answers

<p>Nucleotide hydrolysis promotes dissociation of actin monomers from the filament. (D)</p> Signup and view all the answers

<p>The plus end. (D)</p> Signup and view all the answers

<p>Actin monomers are added to the plus end and removed from the minus end of the filament. (C)</p> Signup and view all the answers

<p>Actin treadmilling provides a mechanism for the bacteria to propel itself through the cytoplasm of a host cell. (D)</p> Signup and view all the answers

<p>Both have two distinct ends with different critical concentrations. (C)</p> Signup and view all the answers

<p>Degradation. (A)</p> Signup and view all the answers

<p>Cc is inversely proportional to the elongation rate, meaning a higher Cc leads to a faster elongation rate. (C)</p> Signup and view all the answers

<p>The relative elongation rates at the minus and plus ends can vary depending on the specific values of $k_{on}$ and $k_{off}$ at each end. (C)</p> Signup and view all the answers

<p>The filament will shrink at the minus end and grow at the plus end, effectively moving the filament in a specific direction. (D)</p> Signup and view all the answers

<p>Treadmilling allows filaments to maintain a constant length despite continuous subunit turnover. (B)</p> Signup and view all the answers

<p>All of the above factors influence the values of $k_{on}$ and $k_{off}$. (D)</p> Signup and view all the answers

<p>All of the above factors contribute to the difference in critical concentration. (D)</p> Signup and view all the answers

<p>$Cc^{-} = k_{off}/k_{on}$ (C)</p> Signup and view all the answers

<p>It highlights that elongation rate, considering both polymerization and depolymerization, is a more accurate measure of filament dynamics than polymerization rate alone. (B)</p> Signup and view all the answers

<p>Microtubule (C)</p> Signup and view all the answers

<p>Mechanical support (A)</p> Signup and view all the answers

<p>α-tubulin (C)</p> Signup and view all the answers

<p>Actin filament (D)</p> Signup and view all the answers

<p>Cytoskeleton (D)</p> Signup and view all the answers

<p>Transporting organelles (C)</p> Signup and view all the answers

<p>Intermediate filaments (D)</p> Signup and view all the answers

<p>Intermediate filament (C)</p> Signup and view all the answers

Hollow cylinders that are part of the cytoskeleton and help in cell shape and division.

Rope-like fibers that provide mechanical support to cells and stabilize their structures.

A network of fibers composed of proteins that give shape and support to cells.

A polymer made from globular actin (G-actin) that plays a role in cell movement and shape.

Composed of α-tubulin and β-tubulin, forming long hollow tubes in cells.

A mesh-like structure made of intermediate filaments that provides support to the nucleus of a cell.

A type of intermediate filament found in epithelial cells that contributes to skin and hair structure.

Their properties include growth, shrinkage, and resilience in cellular activities.

Enzymes that hydrolyze nucleotides, like ATP and GTP.

Globular form of actin that polymerizes to form F-actin.

Filamentous form of actin, made from G-actin subunits.

Enzyme that hydrolyzes ATP to ADP and Pi, involved in actin dynamics.

Enzyme that hydrolyzes GTP to GDP and Pi, crucial for microtubule dynamics.

Stabilizing structure at the growing end of actin or microtubule, promoting growth.

Process of monomers joining to form polymers, such as actin filaments.

Process where polymers break down into monomers, like actin filament disassembly.

The process by which G-actin monomers form F-actin filaments.

The ability of actin to hydrolyze ATP, providing energy for muscle contraction.

The initial step in actin polymerization that is rate-limiting.

Tools, like pyrene conjugated G-actin, used to monitor actin polymerization.

The characteristic curve of actin polymerization, showing a lag phase before rapid growth.

Unstable initial structures that can lead to actin polymerization.

Indicates polymerized actin; its fluorescence is much higher in this form.

Salt influences the reversible polymerization of actin.

The rate at which a polymer grows, defined by a simple equation involving rate constants for incorporation and dissociation.

A numerical value that quantifies the rate of incorporation or dissociation in polymer dynamics.

The concentration of free subunits at which there is no net growth or shrinkage of the polymer.

A state during polymer dynamics where the rate of subunit addition equals the rate of subunit loss.

Occurs when the concentration of subunits exceeds the critical concentration.

Occurs when subunit concentration is below critical concentration.

The rate of change in distance over time, either constant or varying.

Processes describing how subunits are added to or removed from a polymer.

The difference in the number of subunits over time, which determines polymer dynamics.

The characteristic of actin filaments that have a directionality in their growth.

The speed at which filaments grow at their ends, influenced by various factors.

The rate at which filaments grow at the minus end, dependent on k-on and k-off rates.

The rate at which filaments grow at the plus end, higher than the minus end due to a faster k-on.

A dynamic state where subunits are added at one end and lost at the other, keeping filament length constant.

A structure formed by ATP-bound subunits at the plus end, promoting stability and growth.

The rates of addition (k-on) and removal (k-off) of subunits in filament dynamics.

The state where the rates of growth and shrinkage are equal, leading to stable filament length.

The changes in behavior of actin filaments, including growth, shrinkage, and treadmilling.

The growing end of an actin filament where subunits are added.

The end of an actin filament where subunits are lost.

The process where individual actin subunits (G-actin) join to form a filament (F-actin).

The breakdown of nucleotides like ATP, which promotes dissociation of actin filaments.

The locomotion of Listeria using actin treadmilling for motility inside host cells.