Cytoskeleton Overview and Intermediate Filaments
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Questions and Answers

What initiates the power stroke during muscle contraction?

  • Release of Pi from myosin head (correct)
  • Myosin head hydrolyzes ATP
  • Myosin head binds ATP
  • Calcium binds to tropomyosin

Which statement is true regarding myosin and calcium in muscle contraction?

  • Calcium enables tropomyosin to block myosin binding sites
  • Myosin can bind to actin freely without calcium
  • Tropomyosin shifts to expose binding sites when calcium is present (correct)
  • Calcium binds directly to myosin to facilitate contraction

What is the role of ATP in muscle contraction?

  • It binds directly to actin
  • It causes muscle fibers to relax
  • It replaces calcium in muscle fibers
  • It provides energy for the power stroke (correct)

What happens when there is a lack of calcium in muscle contraction?

<p>Tropomyosin remains in place, preventing myosin binding (D)</p> Signup and view all the answers

Which step in the muscle contraction cycle involves the hydrolysis of ATP?

<p>Myosin head hydrolyzes ATP to ADP and Pi (C)</p> Signup and view all the answers

What is the primary role of intermediate filaments in a cell?

<p>Withstanding mechanical stress (C)</p> Signup and view all the answers

Which component of the cytoskeleton is responsible for the movement of flagella and cilia?

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

How do intermediate filaments differ from globular proteins like chymotrypsin?

<p>Intermediate filaments form long chains or filaments (A)</p> Signup and view all the answers

What structural feature allows intermediate filaments to provide tensile strength?

<p>Formation of dimers in an antiparallel arrangement (B)</p> Signup and view all the answers

Which of the following best describes the composition of the nuclear lamina?

<p>Intermediate filaments supporting nuclear structure (C)</p> Signup and view all the answers

Which type of cells commonly feature keratin filaments?

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

What does the coiled-coil structure of intermediate filaments primarily help achieve?

<p>Formation of stable, rope-like filaments (C)</p> Signup and view all the answers

How do intermediate filaments behave during cellular division?

<p>They assemble and disassemble (A)</p> Signup and view all the answers

What type of cell response is mediated by the cytoskeleton?

<p>Movement in response to mechanical forces (B)</p> Signup and view all the answers

What role do hydrophobic amino acids play in the structure of intermediate filaments?

<p>They minimize contact with water to stabilize the dimer formation (B)</p> Signup and view all the answers

What is the function of myosin in relation to actin filaments?

<p>It binds to actin filaments and hydrolyzes ATP to produce movement. (B)</p> Signup and view all the answers

Which steps characterize the process of cell crawling?

<p>Cells form a protrusion that attaches to a surface. (D)</p> Signup and view all the answers

What role do actin-binding proteins play in fibroblast migration?

<p>They assist in the formation of actin bundles. (C)</p> Signup and view all the answers

In muscle contraction, what primarily causes the sarcomere to shorten?

<p>Sliding of actin past myosin filaments. (C)</p> Signup and view all the answers

What distinguishes Myosin-I from Myosin-II?

<p>Myosin-I has a singular tail domain for cargo. (D)</p> Signup and view all the answers

How are actin filaments arranged in the sarcomere?

<p>The plus end is anchored to the Z-disc, and the minus end overlaps with myosin. (A)</p> Signup and view all the answers

What is the key characteristic of muscle myofibrils?

<p>They are composed of tiny assemblies called sarcomeres. (D)</p> Signup and view all the answers

What is the role of the Z-disc in a sarcomere?

<p>It anchors the plus end of actin filaments. (B)</p> Signup and view all the answers

Which of the following statements about actin filaments during contraction is correct?

<p>Neither actin nor myosin filaments shorten. (B)</p> Signup and view all the answers

What is the general structure of myosin molecules?

<p>Myosin molecules have a head domain and a tail domain. (D)</p> Signup and view all the answers

What structural role do intermediate filaments primarily serve?

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

Which of the following statements about microtubules is accurate?

<p>They assist in the movement of cilia and flagella. (D)</p> Signup and view all the answers

What is the main function of ATP in actin filaments?

<p>To control actin polymerization (A)</p> Signup and view all the answers

Which type of intermediate filament is found in epithelial cells?

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

What element primarily anchors microtubules at the centrosome?

<p>Gamma-tubulin (D)</p> Signup and view all the answers

What occurs during muscle contractions involving actin and myosin?

<p>Actin and myosin slide past each other. (C)</p> Signup and view all the answers

What is a function of motor proteins like kinesins and dyneins?

<p>To facilitate movement towards microtubule ends (B)</p> Signup and view all the answers

What characterizes the structure of microtubules?

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

How do actin filaments contribute to cell movement?

<p>Through dynamic treadmilling (A)</p> Signup and view all the answers

What is the structure of intermediate filaments described as?

<p>Coiled-coil dimers (A)</p> Signup and view all the answers

Which protein is primarily involved in muscle contractions?

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

What does GTP hydrolysis influence in microtubules?

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

Which type of filament provides tensile strength to cells?

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

Which statement about microtubule growth is correct?

<p>It occurs only at the plus end. (A)</p> Signup and view all the answers

What are the main subunits that make up microtubules?

<p>Alpha and beta-tubulin (A)</p> Signup and view all the answers

Which end of a microtubule is considered the growing end?

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

What role do motor proteins play in relation to microtubules?

<p>They transport intracellular materials (A)</p> Signup and view all the answers

What term describes the process where monomers are simultaneously added to one end and removed from the other end of an actin filament?

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

What is the diameter of actin filaments?

<p>7 nm (D)</p> Signup and view all the answers

Which of the following structures involve stable microtubules moved by dynein?

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

How does GTP hydrolysis affect microtubule growth?

<p>It controls the addition of GDP-bound tubulin (C)</p> Signup and view all the answers

What is the primary function of microtubules in relation to cell shape?

<p>To selectively stabilize and polarize a cell (C)</p> Signup and view all the answers

What is the role of actin-binding proteins in the dynamics of actin filaments?

<p>They regulate the behavior of actin monomers (A)</p> Signup and view all the answers

What is the primary structural arrangement of eukaryotic flagella?

<p>9+2 array (D)</p> Signup and view all the answers

What provides ATP energy for motor proteins to function on microtubules?

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

What type of diseases can result from the disruption of intermediate filaments?

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

Which of the following best describes the function of microtubules in cell division?

<p>They guide the separation of chromosomes (D)</p> Signup and view all the answers

How are free actin monomers maintained within a cell?

<p>They are balanced with filamentous actin (D)</p> Signup and view all the answers

Flashcards

Cytoskeleton definition

A network of protein filaments throughout the cytoplasm, organizing cellular components and enabling movement.

Cytoskeleton function (movement)

Facilitates movement of organelles and vesicles, entire cells (like cilia, flagella) and in response to signals.

Structural protein shape

Tend to be long filaments, unlike globular proteins like enzymes.

Intermediate filaments type

A type of protein filament in the cytoskeleton that resists mechanical stress (like stretching).

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Intermediate filament function

Provide tensile strength, resisting forces that stretch cells.

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Intermediate filament structure

Rope-like, 10 nm thick, assembled from coiled-coil protein subunits.

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Nuclear lamina composition

A structure within the nucleus composed of intermediate filaments.

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Intermediate filament classes

Keratin filaments, a major class, are found in many epithelial cells.

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Intermediate filament assembly

Dimers wrap together antiparallel to form tetramers, further associating into rope-like structures.

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Cell Crawling

Cells move by extending protrusions, attaching to a surface, and pulling themselves forward, using actin polymerization.

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Intermediate Filament Rebar analogy

They are like rebar in concrete, providing strength and preventing cracking when the cell is stretched.

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Cortical Actin

Actin filaments organized just beneath the cell membrane, crucial for cell crawling.

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Myosin-I

A type of myosin that is a single-headed motor protein.

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Muscle Contraction

The sliding of actin and myosin filaments within muscles, causing shortening of the muscle.

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Myosin-II

Myosin structure moving filaments in opposite directions.

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Myofibril

The contractile elements of a muscle cell.

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Sarcomere

The functional unit of a myofibril: a repeating section of actin and myosin.

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Actin Filament Structure

Actin filaments are assembled from actin monomers. These filaments have a plus and minus end.

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Z-disc

Region where the plus ends of actin filaments are anchored.

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Filament Sliding

Actin and myosin filaments slide past each other to shorten the sarcomere without changing their lengths.

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Intermediate filaments

A class of protein filaments that provide mechanical strength to cells.

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Microtubules

Hollow tubes made of tubulin subunits, crucial for cell organization and movement.

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Microtubule polarity

Microtubules have a (+) end (growing) and a (-) end (non-growing).

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Centrosome

A microtubule-organizing center in animal cells, where microtubules originate.

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Tubulin

Globular protein subunits that make up microtubules.

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GTP hydrolysis

The process that controls microtubule growth and shrinkage by adding or removing tubulin subunits.

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Actin filaments

Protein filaments crucial for cell shape and movement.

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Actin polymerization

The process of actin subunits coming together to form filaments, influenced by ATP.

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Treadmilling

The process in which actin filaments continually add monomers at one end while losing others at the opposite end.

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Actin-binding proteins

Proteins that regulate the behavior of actin monomers, influencing filament formation.

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Motor proteins

Proteins that use ATP energy to move along microtubules and drive intracellular transport.

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Kinesin

A motor protein that moves along microtubules in a direction towards the plus end.

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Dynein

A motor protein that moves along microtubules in a direction towards the minus end.

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Cilia and Flagella

Cellular appendages containing microtubules and dynein, used for movement.

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Muscle contraction steps

A series of steps where ATP hydrolysis powers the interaction between myosin and actin, causing muscle fibers to shorten.

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Calcium's role in muscle contraction

Calcium ions cause a shift in tropomyosin, exposing myosin binding sites on actin, enabling muscle contraction.

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Myosin-actin interaction

Myosin heads attach and detach from actin filaments, leading to the sliding of these filaments past each other. This is the fundamental mechanism of muscle contraction.

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Tropomyosin's role

Tropomyosin, in the absence of calcium, blocks myosin binding sites on actin. When calcium is present, tropomyosin repositions, allowing myosin to bind and contract.

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ATP's role in muscle contraction

ATP provides the energy for the power stroke movement. It is hydrolyzed to detach myosin from actin; then, ATP reattaches to myosin, causing it to reset for re-binding.

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What is the function of microtubules?

They play a role in cell division, organelle movement, and the formation of cilia and flagella.

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What are the three main types of cytoskeletal filaments?

Microtubules, intermediate filaments, and actin filaments.

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What are actin filaments made of?

Globular actin monomers that polymerize to form long filaments.

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What is the cytoskeleton?

A network of protein filaments that extends throughout the cytoplasm. It provides structure, support, and aids in movement within cells.

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Microtubule ends

Microtubules have a plus end and a minus end. The plus end grows, while the minus end is usually anchored.

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What are microtubules made of?

Tubulin dimers, composed of alpha and beta tubulin subunits.

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What does actin do?

It is crucial for cell shape, movement, and muscle contraction.

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Why is understanding the cytoskeleton important?

Understanding the cytoskeleton is crucial for comprehending cell structure, function, and movement, as well as for understanding various diseases.

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How are microtubule and actin filaments similar?

Both are dynamic structures that can grow and shorten, and their assembly is regulated by the hydrolysis of ATP or GTP.

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What are motor proteins?

Proteins that use ATP to move along cytoskeletal filaments.

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What are kinesins and dyneins?

Motor proteins that move along microtubules. Kinesins move towards the plus end, while dyneins move towards the minus end.

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What is the difference between microtubules and actin filaments?

Microtubules are hollow tubes and are involved in organelle movement and cell division. Actin filaments are solid and play a role in cell shape and movement.

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How does muscle contraction work?

Myosin II motor proteins interact with actin filaments, causing them to slide past each other and shorten the muscle fiber.

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What is the role of calcium in muscle contraction?

Calcium ions trigger the binding of myosin to actin, initiating muscle contraction.

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Study Notes

Cytoskeleton Overview

  • The cytoskeleton supports cells.
  • It's a network of protein filaments throughout the cytoplasm.
  • It's involved in organizing and moving intracellular components.

Types of Protein Filaments

  • Intermediate Filaments:

    • These filaments provide structural support and withstand mechanical stress.
    • They are rope-like, about 10nm in diameter.
    • Found throughout the cytoplasm, in the nucleus (nuclear lamina), and sometimes anchoring neighboring cells.
    • They fold into coiled-coils.
    • Strands form alpha-helices that pair in dimers.
    • Hydrophobic amino acids interact to minimize contact with water.
    • Dimers wrap to form staggered tetramers and then rope-like filaments.
    • Make up the nuclear lamina.
    • They respond to stress when cells are stretched.
    • Intermediate filaments can be categorized as: keratin, vimentin, neurofilaments, and nuclear lamins.
    • Keratin filaments make up skin, hair, claws, and more; humans have more than 50 keratin genes.
    • Disruption of intermediate filaments can lead to disease like Epidermolysis bullosa, muscular dystrophy, Neurodegeneration, and Progeria.

  • Microtubules:

    • Microtubules have a key role in moving organelles, cell compartments, cell division, and movement of cilia and flagella components.
    • Microtubules are hollow tubes composed of alpha- and beta-tubulin.
    • They have polarity with a growing (plus) end and a non-growing (minus) end, which is usually anchored.
    • Tubulin polymerizes from nucleation sites on a centrosome.
    • Gamma (γ) tubulin is the nucleation site that anchors the microtubule.
    • GTP hydrolysis controls microtubule growth.
    • GTP-bound tubulin molecules bind to the growing end; GDP-bound tubulin molecules are released from the growing end.
    • Involves dynamic instability (growing, shrinking).
    • They guide movement of organelles, vesicles, and macromolecules.
    • Motor proteins (kinesin, dynein) use ATP energy to move along microtubules.
    • They are crucial for intracellular transport.
    • Cilia and flagella contain stable microtubules moved by dynein.
    • They beat in a whip-like fashion, used in things like respiration and sweeping mucus.
    • Eukaryotic flagella and cilia have a characteristic 9+2 array with dynein arms.

  • Actin Filaments:

    • Actin filaments are essential for cell shape and movement.
    • These filaments are composed of globular actin monomers.
    • They are about 7nm in diameter.
    • Actin filaments are polarized, having plus and minus ends.
    • ATP hydrolysis controls actin polymerization.
    • High concentrations of actin cause both ends to grow.
    • Intermediate concentrations cause treadmilling (monomers removed from minus end added to plus end).
    • Actin-binding proteins control the behavior of actin monomers.
    • Cell crawling depends on cortical actin.
    • It pushes out protrusions to form filopodia and lamellipodia. These attach to the cell surface to cause movement.
    • Actin associates with myosin to form contractile structures.
    • Myosin uses energy from ATP to pull itself toward the plus end of actin filaments.
    • Myosin-I moves organelles along actin, and Myosin-II moves both ends of actin filaments.

Muscle Contraction

  • Muscle contraction depends on interacting actin and myosin filaments and involves the sliding of actin filaments past myosin filaments.
  • Myosin heads hydrolyze ATP to move along actin, causing contraction.
  • Myosin cannot bind to actin in the absence of calcium.
  • Tropomyosin blocks myosin binding sites; shifts with Ca2+ binding.
  • Muscle contraction involves a cycle: ATP-binding, ATP-hydrolysis, power stroke, and detachment.

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Description

This quiz covers the essential functions and structure of the cytoskeleton, focusing primarily on intermediate filaments. Learn about their role in providing structural support and their various types, including keratin and vimentin. Test your understanding of how these filaments contribute to cellular organization and resilience.

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