Cytoskeleton and Microtubules Overview
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Cytoskeleton and Microtubules Overview

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What is the primary role of microtubules during cell division?

  • They play a role in lipid synthesis during cytokinesis.
  • They provide structural support to the cell membrane.
  • They facilitate the movement of the nucleus to the cell periphery.
  • They are involved in the formation of spindle fibers. (correct)

    • Which of the following correctly describes the composition of microtubules?

  • They are formed from single protein strands without any subunits.
  • They consist of multiple identical protein units arranged in a ring.
  • They are composed of heterodimers of α- and β-tubulin. (correct)
  • They are made exclusively from actin proteins.

    • What type of junction primarily allows for communication between adjacent cells?

  • Adhering junctions
  • Gap junctions (correct)
  • Desmosomes
  • Tight junctions

    • What is the diameter range of microtubules?

    <p>25 to 30 nm</p> Signup and view all the answers

    What structure do centrioles primarily contribute to in animal cells?

    <p>Development of microtubule spindle fibers.</p> Signup and view all the answers

    What is the primary arrangement of microtubules within a centriole?

    <p>9 sets of triplets arranged as a cylinder</p> Signup and view all the answers

    What structure is located at one end of the mature centriole?

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

    How do centrioles typically duplicate prior to cell division?

    <p>Through the growth of a new daughter centriole at right angles to the old centriole</p> Signup and view all the answers

    What is the role of the centrosome in cellular structure?

    <p>It acts as the main microtubule organizing centre of the cell</p> Signup and view all the answers

    What is the characteristic structural configuration of a centriole described as '9 - 3'?

    <p>9 triplet microtubules with one complete and two incomplete</p> Signup and view all the answers

    What are spot desmosomes primarily responsible for?

    <p>Connecting cells to each other via intermediate filaments</p> Signup and view all the answers

    What is the key difference between spot desmosomes and hemidesmosomes?

    <p>Spot desmosomes connect cells to each other, while hemidesmosomes connect to the basal lamina</p> Signup and view all the answers

    What is the pore size of the hydrophilic channel formed by gap junctions?

    <p>1.5 nm</p> Signup and view all the answers

    What protein forms the transmembrane components of gap junctions?

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

    How do gap junctions contribute to cardiac muscle function?

    <p>They enable the transmission of electrical impulses between cardiac muscle cells</p> Signup and view all the answers

    What is the primary protein that microfilaments are largely formed of?

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

    Which type of intermediate filament is primarily found in nerve axons?

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

    What is the typical diameter range of intermediate filaments?

    <p>7-11 nm</p> Signup and view all the answers

    How are microfilaments primarily organized within cells?

    <p>In networks or bundles just below the plasma membrane</p> Signup and view all the answers

    Which type of protein is found within Type III intermediate filaments?

    <p>Vimentin-like proteins</p> Signup and view all the answers

    Which structure is typically produced by microfilaments?

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

    What is the structural arrangement of motile cilia?

    <p>9+2 arrangement</p> Signup and view all the answers

    Intermediate filaments can be described as having which of the following characteristics?

    <p>Heterogeneous in composition with multiple types present</p> Signup and view all the answers

    What primarily serves as the nucleation site for microtubules in the centrosome?

    <p>Gamma-tubulin rings</p> Signup and view all the answers

    Which type of junction acts as a principal mechanical interlink between cells?

    <p>Adhesion Junctions</p> Signup and view all the answers

    What is the typical width of the intercellular space separating cells in tissues?

    <p>20-30 nm</p> Signup and view all the answers

    Which type of cadherin is specifically associated with epithelial cells?

    <p>E-cadherin</p> Signup and view all the answers

    What is a consequence of cadherin loss during cancer development?

    <p>Increased metastasis</p> Signup and view all the answers

    Which type of cell junction is characterized by sealing adjacent cells together to prevent the passage of materials?

    <p>Tight Junctions</p> Signup and view all the answers

    What links cadherins to the cytoskeleton in adherens junctions?

    <p>Linker proteins</p> Signup and view all the answers

    Which type of junction allows for direct communication between adjacent cells?

    <p>Gap Junctions</p> Signup and view all the answers

    Study Notes

    Cytoskeleton

    • Animal cells maintain their three-dimensional structure through a network called the cytoskeleton
    • The cytoskeleton is made up of three main components: microtubules, microfilaments, and intermediate filaments
    • All three components are assembled from cytoplasmic proteins.

    Microtubules

    • Microtubules are hollow cylinders with a diameter of 25-30nm
    • They are composed of 13 subunits arranged in a left-handed helix
    • Each subunit is a heterodimer of two proteins: alpha- and beta-tubulin
    • They are the thickest filaments and are rigid
    • They have a + and a - end

    Function of Microtubules

    • They form the axoneme of cilia and flagella
    • They form the components of centrioles
    • They form the spindle fibers during cell division
    • They are involved in intracellular movement in nerve cell axons

    Microtubules: Motile vs Non-Motile

    • Motile microtubules have a 9+2 structure and are found in cilia and flagella
    • Non-motile microtubules have a 9+0 structure and are found in primary cilia, such as those in kidney cells.

    Microfilaments

    • Also known as Actin filaments
    • Solid filaments with a diameter of 5-7nm
    • Primarily composed of the protein actin
    • Found in most animal cells and some plants cells
    • Concentrated in networks or bundles just below the plasma membrane
    • Involved in forming intestinal microvilli

    Intermediate Filaments

    • Heterogeneous in composition: Each cell will have more than one type, with one usually dominating
    • Five main types based on the protein involved:
      • Type I & II - keratins (acidic and basic)
      • Type III - vimentin-like proteins (found in cells of mesodermal origin)
      • Type IV - neurofilaments (found in nerve axons)
      • Type V - nuclear laminins (form the nuclear lamina)
    • Rope-like filaments found in most cells
    • Size intermediate to actin filaments and microtubules
    • Solid filaments with a diameter of 7-11nm
    • Non-alpha-helical (globular) domain at the N and C-termini, surrounding the alpha-helical rod domain.

    Centrioles

    • Found in all animal cells and ciliated plant cells
    • Located in the cytoplasm, near the nucleus
    • Often associated with the Golgi apparatus
    • The area where they are found is called the microtubule organizing centre
    • Typically two cylindrical structures arranged at right angles to each other

    Centrioles: Structure

    • Composed of 9 sets of triplets arranged in a cylinder.
    • Known as a 9x3 structure (9+0 structure)
    • Each triplet consists of three microtubules:
      • Set A is complete.
      • Set B and C share portions of their walls.
    • A cartwheel structure is found at one end of the centriole, protruding from the outer surface at the proximal end of a mature centriole.
    • Fibrous structures connect the two centriole cylinders.

    Centrioles: Function

    • Centrioles replicate and move to opposite poles of the cell before cell division
    • New daughter centrioles grow at right angles to the 'old' centriole
    • One new centriole and one old centriole form areas known as centrosomes.

    Centrosomes

    • The centrosome is the main microtubule organizing centre of the cell.
    • Composed of two orthogonally arranged centrioles
    • Contain pericentriolar material (purple), responsible for microtubule nucleation and anchoring

    Centrosomes: Microtubule Organization

    • Microtubules radiate from the centrosome, but they are not organized by the centrioles.
    • Microtubules originate from gamma-tubulin rings in the centrosomal matrix (distal appendages).
    • Each gamma-tubulin ring acts as a nucleation site for one microtubule.
    • An aster of microtubules forms the visible spindle fibers during cell division.
    • Some spindle fibers bind to the chromosomes at the centromere.

    Cell Junctions

    • Most cells in tissues are attached to other cells.
    • Cells are separated by an intercellular space of 20-30nm.
    • Specialized intercellular junctions maintain more direct contact between membranes.
    • Three types of cell junctions exist:
      • Adhesion Junctions (Adherens and Desmosomes)
      • Tight Junctions
      • Gap Junctions

    Adhesion Junctions

    • Principle mechanical interlinks between cells, serving as strong connections between epithelial cells.
    • Two types:
      • Desmosomes
      • Adherens junctions
    • The intercellular space is normal (30nm) and filled with transmembrane proteins called cadherins.

    Cadherins

    • Form links to cytoplasmic structures.
    • Connect the membrane to the cytoskeleton
    • Three types:
      • E-cadherin – epithelial
      • N-cadherin – neuronal
      • P-cadherin – placental
    • Cadherin loss is associated with cancer and metastases.

    Adherens Junctions

    • Cadherin attachment occurs via linker proteins to actin microfilaments in the cytoplasm.
    • Serve as a bridge connecting the actin cytoskeleton of neighboring cells.

    Desmosomes

    • Disc-like plaques in the cytoplasm, 20nm thick and 0.2-0.3µm in diameter.
    • Two types:
      • Spot desmosomes (Macula adherens), which are like spot rivets connecting cells via intermediate filaments.
      • Hemidesmosomes connect the bottom surface of epithelial cells to the underlying basal lamina.
      • The transmembrane linker proteins in hemidesmosomes are integrins.

    Hemidesmosomes

    • Integrins are the transmembrane linker proteins in hemidesmosomes.

    Gap Junctions

    • Involved in the interchange of small inorganic ions and molecules between adjacent cells.
    • The intercellular space is reduced to 2-4nm.
    • Each membrane contains a hexagonal array of proteins.
    • The transmembrane proteins are called connexins.

    Gap Junctions: Structure

    • Arrays in opposing membranes align.
    • This forms a hydrophilic channel with a pore size of 1.5nm in diameter.
    • Gap junctions are associated with intercalated discs in cardiac muscle, facilitating the transmission of electrical impulses.

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    Description

    Explore the structure and function of the cytoskeleton, focusing on microtubules in animal cells. This quiz covers microtubule composition, their roles in cell division, and distinctions between motile and non-motile microtubules. Test your knowledge on the essential components that maintain cellular integrity and movement.

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