Cytoskeletal Structures Quiz
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Questions and Answers

What is the outer diameter of microtubules?

  • 50 nm
  • 100 nm
  • 25 nm (correct)
  • 10 nm

Actin filaments are more rigid than microtubules.

False (B)

What is the primary protein that makes up microtubules?

tubulin

Intermediate filaments have a diameter of about _____ nm.

<p>10</p> Signup and view all the answers

Which structure is known as the microtubule-organizing center?

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

Match the following cytoskeletal structures with their characteristics:

<p>Microtubules = Made of tubulin and have a diameter of 25 nm Intermediate filaments = Rope-like fibers with a diameter of 10 nm Actin filaments = Dynamic structures used for cell movement Nuclear lamina = Meshwork beneath the inner nuclear membrane</p> Signup and view all the answers

The structural rearrangement in a cell requires significant energy when conditions change.

<p>False (B)</p> Signup and view all the answers

What type of projections do actin filaments form for exploration and movement?

<p>filopodia, lamellipodia, and pseudopodia</p> Signup and view all the answers

What is the purpose of adding premade nuclei during polymerization?

<p>To reduce or eliminate the lag phase (B)</p> Signup and view all the answers

The lag phase corresponds to the time taken for polymer disassembly.

<p>False (B)</p> Signup and view all the answers

What are the two ends of an actin filament or microtubule called?

<p>plus end and minus end</p> Signup and view all the answers

The ___ phase occurs as monomers add to the exposed ends of the growing filament.

<p>growth</p> Signup and view all the answers

Match the phases of polymerization with their descriptions:

<p>Lag Phase = Time taken for nucleation Growth Phase = Monomer addition causing filament elongation Equilibrium Phase = State when growth balances shrinkage Plus End = Fast-growing end of the filament</p> Signup and view all the answers

Which of the following is true regarding the growth rates of the plus and minus ends?

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

The equilibrium phase is reached when the polymerization process is halted.

<p>False (B)</p> Signup and view all the answers

The slow-growing end of a filament is referred to as the ___ end.

<p>minus</p> Signup and view all the answers

What structures are primarily involved in the motility of neutrophils?

<p>Lamellipodia and filopodia (A)</p> Signup and view all the answers

Filament nucleation involves the spontaneous binding of actin subunits without any stabilization.

<p>False (B)</p> Signup and view all the answers

What is the role of the actin cytoskeleton in neutrophils?

<p>It enables rapid disassembly and reassembly for changing orientation and movement.</p> Signup and view all the answers

The process of forming a stable group of actin subunits is known as ______.

<p>nucleation</p> Signup and view all the answers

Match each term with its corresponding description:

<p>Actin Filaments = Dynamic structures that enable cell motility Nucleus = The stable group formed during filament nucleation Lamellipodia = Wide, sheet-like protrusions at the cell's leading edge Filopodia = Narrow, finger-like projections of the cell</p> Signup and view all the answers

Which of the following best describes how actin filaments are formed?

<p>Actin filaments form through stable oligomers called nuclei which allow for rapid elongation. (B)</p> Signup and view all the answers

A trimer of actin molecules has a high stability that allows for further monomer addition.

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

What is the consequence of rapid disassembly and reassembly of actin in neutrophils?

<p>It allows neutrophils to quickly change orientation and direction of movement.</p> Signup and view all the answers

What is the primary factor that determines the equilibrium constant for subunit association in polymerization?

<p>Ratio of kon to koff (A)</p> Signup and view all the answers

The same subunit interactions are broken when a subunit is lost from either end of the polymer.

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

What are the products formed when ATP is hydrolyzed in actin polymerization?

<p>ADP</p> Signup and view all the answers

In the context of polymerization, the form that is usually added to the filament is the _____ form.

<p>T</p> Signup and view all the answers

When K is greater than C (K > C), what happens to the ends of the polymer?

<p>Both ends grow (C)</p> Signup and view all the answers

The hydrolysis of nucleotide at the end of polymerization increases the binding affinity of subunits.

<p>False (B)</p> Signup and view all the answers

Which molecule does tubulin carry that is converted to GDP upon assembly?

<p>GTP</p> Signup and view all the answers

Match the following forms of monomers with their respective binding states:

<p>T = Monomer carrying ATP or GTP D = Monomer carrying ADP or GDP ATP = Initiator of actin polymerization GTP = Initiator of tubulin polymerization</p> Signup and view all the answers

Flashcards

Microtubules

Long, hollow cylinders made of tubulin protein, crucial for cell shape, intracellular transport, and cell division.

Centrosome

A microtubule-organizing center (MTOC) that serves as a starting point for microtubule assembly.

Intermediate Filaments

Rope-like fibers with a diameter of about 10 nm, made of intermediate filament proteins, providing mechanical strength and structural support to cells.

Nuclear Lamina

A meshwork of intermediate filaments located beneath the inner nuclear membrane, providing structural support to the nucleus.

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Intermediate Filaments in Epithelium

Specialized structures that extend across the cytoplasm, attaching to cell junctions and strengthening the entire epithelium.

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Cell Surface Projections

Dynamic cell-surface projections like filopodia, lamellipodia, and pseudopodia, formed by actin filaments, allowing cells to explore and move.

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Dynamic Nature of Cytoskeleton

The ability of cytoskeletal components to constantly rearrange themselves, allowing cells to adapt quickly to changing conditions.

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Structural Rearrangement in Cells

The process of changing or maintaining large-scale cytoskeletal structures, requiring minimal energy due to the dynamic nature of components.

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Lamellipodium

A protrusion at the leading edge of a cell, driven by the polymerization of actin filaments.

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Filopodium

A thin, finger-like projection at the leading edge of a cell, composed of bundled actin filaments.

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Actin Filament Nucleation

The process of forming a new actin filament from individual actin monomers.

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Actin Polymerization

The assembly of actin filaments from actin monomers, leading to cell movement and changes in shape.

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Stable Actin Oligomer

The stabilization of actin filaments by the interaction between multiple actin monomers.

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Actin Filament (Polymer)

An actin filament is a long, helical polymer, formed by the association of multiple actin monomers.

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Actin Depolymerization

The process of breaking down Actin filaments back into individual actin monomers.

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Actin and Cell Motility

Actin filaments are essential for cellular movement and structural changes.

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Lag phase

The initial stage of polymerization where monomers assemble into small, stable structures called nuclei.

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Growth phase

The period during polymerization where monomers are added to the ends of existing nuclei, causing rapid filament elongation.

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Equilibrium phase

The state reached when the rate of monomer addition to filaments equals the rate of monomer dissociation, resulting in no net change in filament length.

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Plus end

The end of a filament where monomers add at a faster rate, causing a net growth.

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Minus end

The end of a filament where monomers add at a slower rate, causing a net shrinkage.

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Nucleation

The process of forming a nucleus, or a small, stable cluster of monomers, which is the starting point for filament assembly.

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Effect of premade nuclei on polymerization

Adding pre-made nuclei to a solution speeds up polymerization by skipping the slow nucleation phase.

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Conformational change in subunits during polymerization

Subunits undergo a conformational change when they join a filament, impacting the rate of assembly at different ends.

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Polymerization

The association of monomers into a polymer, where the addition and removal of monomers occur at both ends of the polymer.

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Critical Concentration (Cc)

The concentration of free monomers required for a polymer to remain in a steady state, neither growing nor shrinking.

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Equilibrium Constant (K)

The ratio of the rate constant for monomer dissociation (koff) to the rate constant for monomer association (kon). It determines the equilibrium constant for the association of monomers into a polymer.

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Nucleotide Hydrolysis

The process of hydrolyzing a bound nucleotide (ATP or GTP) to a tightly bound ADP or GDP after a monomer assembles into a polymer. This reduces the binding affinity of the monomer, making it more likely to dissociate.

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T Form (T)

The state of a monomer carrying a bound ATP molecule. This form typically associates with the polymer, adding to its growth.

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D Form (D)

The state of a monomer carrying a bound ADP molecule. This form usually dissociates from the polymer, contributing to its shrinking.

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Study Notes

The Cytoskeleton

  • Cells must organize themselves in space and interact mechanically with each other and their environment to function correctly.
  • They need to maintain proper shape, structural integrity, and be able to change shape and move.
  • Cellular components are rearranged to adapt to changing circumstances.
  • This function relies on a system of filaments called the cytoskeleton.

Cytoskeleton Components

  • The cytoskeleton is made of three main protein filament families:
    • Actin filaments (microfilaments)
    • Microtubules
    • Intermediate filaments
  • Each filament type has unique mechanical properties, dynamics, and biological roles.
  • These filaments must work together to give cells strength, shape, and the ability to divide and move.

Actin Filaments (Microfilaments)

  • Actin filaments are helical polymers of actin protein.
  • They have a diameter of 8 nm.
  • They form linear bundles, two-dimensional networks and three-dimensional gels.
  • Most highly concentrated in the cortex, just below the plasma membrane.
  • They play roles in cell surface projections (e.g., microvilli, stress fibers), cell locomotion and cell division.

Microtubules

  • Long, hollow cylinders made of tubulin protein.
  • Have an outer diameter of 25 nm
  • More rigid than actin filaments.
  • Typically have one end attached to a microtubule-organizing center (MTOC), often a centrosome.
  • Involved in intracellular transport, organelle positioning and cell division (forming the mitotic spindle).

Intermediate Filaments

  • Rope-like fibers with a diameter of about 10 nm.
  • Consist of a large and heterogeneous family of intermediate filament protein.
  • Form a meshwork called the nuclear lamina beneath the inner nuclear membrane.
  • Provide mechanical strength across the cytoplasm.
  • Found in epithelial tissues and other tissues, strengthening these tissues.

Cytoskeleton Dynamics

  • Cytoskeletal structures can change or persist based on cell needs.
  • The components of the structure are constantly changing.
  • Rearrangements do not require a lot of energy.

Cytoskeleton and Cell Division

  • During cell division, cytoskeletal filaments (actin and microtubules) are reorganized in the cell.
  • Actin filaments are rearranged, and the cell becomes spherical in shape.
  • Microtubules form a bipolar mitotic spindle, ensuring duplicated chromosomes are aligned and segregated.
  • New daughter cells inherit reorganized cytoskeletons, enabling them to move and function independently.

Cytokinesis (Cell Division)

  • The cytoskeleton (specifically actin fibers) forms contractile rings during cell division.
  • These rings pinch the cell in two, separating the daughter cells.

Accessory Proteins

  • Numerous accessory proteins regulate and link filaments to other parts of the cell.
  • They control assembly of filaments in specific locations.
  • Include molecular motors that convert ATP hydrolysis energy to mechanical force.
  • Control the movement of organelles and filaments themselves.

Nucleation

  • Actin and tubulin subunits assemble into filaments.
  • Nucleation is the rate-limiting step.
  • It involves the formation of an initial oligomer or nucleus.
  • The nucleus is stabilized and further subunits attach rapidly.

Critical Concentration

  • The critical concentration (Cc) is the concentration of free subunits that equals the rate of subunit loss at equilibrium.
  • It's important in filament growth as it establishes a threshold for subunit addition.
  • At equilibrium, the addition of subunits equals the loss of subunits.

Polymerization Time Course

  • Polymerization of filaments has three phases: lag, growth, and equilibrium.
  • The lag phase is the time needed for nucleation.
  • The growth phase is when the filament elongates because monomers attach to exposed ends.
  • The equilibrium phase is reached when the rate of elongation and shrinkage/depolymerization is balanced.

Plus and Minus Ends

  • Filament ends have different growth rates.
  • The plus end is faster, the minus end slower in growth.
  • Different subunit conformations affect growth rates.
  • Hydrolysis of ATP or GTP (in microtubules) influences filament growth at each end.

Other Important Considerations

  • Protein filaments can be found in a wide variety of shapes and sizes.
  • Differences in subunit connections produce stable or dynamic structures.
  • The cytoskeleton's organization is critical for cellular functions and communication.

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Cytoskeleton 1-23 PDF

Description

Test your knowledge on the cytoskeletal components of cells, including microtubules, actin filaments, and intermediate filaments. This quiz covers their structures, functions, and dynamics. See how well you understand the role these elements play in cell organization and movement.

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