Microtubule Structure
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Questions and Answers

What are the major structural elements of the cytoskeleton?

  • Actin, myosin, tropomyosin
  • Microfilaments, microtubules, intermediate filaments (correct)
  • Ribosomes, endoplasmic reticulum, Golgi apparatus
  • DNA, RNA, proteins

    • What are microtubules composed of?

  • Tubulin subunits (correct)
  • Myosin subunits
  • Keratin subunits
  • Actin subunits

    • Which bacterial cytoskeletal element is involved in DNA segregation and cell shape?

  • Crescentin
  • Actin-like MreB (correct)
  • Myosin-like ParM
  • Tubulin-like FtsZ

    • What are microfilaments essential components of?

    <p>Muscle fibrils</p> Signup and view all the answers

    What has research shown about the cytoskeleton?

    <p>It is dynamically assembled and disassembled</p> Signup and view all the answers

    What are intermediate filaments composed of?

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

    What are the protein building blocks of microtubules?

    <p>Tubulin heterodimers</p> Signup and view all the answers

    What contributes to the dynamic instability of microtubules?

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

    Where do microtubules originate from?

    <p>Microtubule-organizing centers (MTOCs)</p> Signup and view all the answers

    What is the function of microtubule-associated proteins (MAPs)?

    <p>Regulating microtubule dynamics and stability</p> Signup and view all the answers

    What type of polymerization do microtubules undergo?

    <p>Reversible polymerization</p> Signup and view all the answers

    What is the role of microtubules in cancer treatment?

    <p>Targeting microtubule dynamics</p> Signup and view all the answers

    Which type of proteins bind at regular intervals along a microtubule wall?

    <p>Microtubule-associated proteins (MAPs)</p> Signup and view all the answers

    Which proteins promote depolymerization of microtubules?

    <p>Stathmin/Op18</p> Signup and view all the answers

    What do some microtubule-binding proteins use ATP for?

    <p>To drive vesicle or organelle transport</p> Signup and view all the answers

    Which proteins act at the ends of microtubules and promote the peeling of subunits from the ends?

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

    What is the function of katanin in relation to microtubules?

    <p>Severing microtubules</p> Signup and view all the answers

    Which proteins prevent the polymerization of tubulin heterodimers?

    <p>Stathmin/Op18</p> Signup and view all the answers

    What do microtubule-binding proteins use ATP for, in some cases?

    <p>To generate sliding forces between microtubules</p> Signup and view all the answers

    What type of proteins regulate microtubule structure?

    <p>Microtubule-associated proteins (MAPs)</p> Signup and view all the answers

    What is the main function of microfilaments?

    <p>Muscle contraction</p> Signup and view all the answers

    What is the structural core of microvilli composed of?

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

    What does actin polymerize to form?

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

    What do G-actin molecules polymerize to form?

    <p>F-actin</p> Signup and view all the answers

    How are F-actin filaments structured?

    <p>Two linear strands of polymerized G-actin wound into a helix</p> Signup and view all the answers

    What is the orientation of all the actin monomers in the microfilament filament?

    <p>They have the same orientation</p> Signup and view all the answers

    What are the fundamental subunits of intermediate filament proteins?

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

    How long is the central rodlike domain of intermediate filament proteins?

    <p>310 to 318 amino acids</p> Signup and view all the answers

    What role do intermediate filaments play in tissues?

    <p>Tension-bearing role</p> Signup and view all the answers

    What is the structure of the basic unit of intermediate filaments?

    <p>Two intertwined IF polypeptides</p> Signup and view all the answers

    Which cytoskeletal element resists bending when a cell is compressed?

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

    Which proteins connect intermediate filaments, microfilaments, and microtubules?

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

    What is the primary function of microfilaments?

    <p>Serve as contractile elements</p> Signup and view all the answers

    What is the composition of a tetrameric protofilament of intermediate filaments?

    <p>Two aligned dimers</p> Signup and view all the answers

    What is the name of the protein that binds to actin microfilaments in a distinctive arrowhead pattern?

    <p>Myosin subfragment 1 (S1)</p> Signup and view all the answers

    What is the plus end of microfilaments called?

    <p>Barbed end</p> Signup and view all the answers

    Which protein binds a large amount of free G-actin?

    <p>Thymosin β4</p> Signup and view all the answers

    What is the function of ADF/cofilin?

    <p>Binds ADP-G-actin and F-actin to increase turnover of ADP-actin at the minus end</p> Signup and view all the answers

    Which protein is important in forming loose networks of crosslinked actin filaments?

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

    What complex is activated by proteins like WASP and WAVE/Scar to form a dendritic network of actin?

    <p>Arp2/3 complex</p> Signup and view all the answers

    What does contractility refer to in the context of cell motility?

    <p>The shortening of muscle cells</p> Signup and view all the answers

    What is the primary function of microfilament-based motility?

    <p>Muscle contraction</p> Signup and view all the answers

    What do molecular motors couple ATP hydrolysis to?

    <p>Changes in shape &amp; addition of the motor protein</p> Signup and view all the answers

    What are microtubules and microfilaments likened to in the context of motile systems?

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

    What is the function of motor proteins at the molecular level?

    <p>Produce motion</p> Signup and view all the answers

    What is an example of microtubule-based motility?

    <p>The sliding of microtubules in cilia and flagella</p> Signup and view all the answers

    What is the structure that gives myofibrils a pattern of alternating dark and light bands?

    <p>A bands</p> Signup and view all the answers

    Which protein constitutes a calcium-sensitive switch that activates contraction in striated muscle?

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

    What is the primary component of thick filaments in skeletal muscle?

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

    What does the sliding filament model propose as the cause of muscle contraction?

    <p>Thin filaments sliding past thick filaments</p> Signup and view all the answers

    What is the arrangement of myosin in a thick filament?

    <p>Staggered fashion</p> Signup and view all the answers

    What is the function of tropomyosin in skeletal muscle?

    <p>Regulating the interaction of actin and myosin</p> Signup and view all the answers

    What gives rise to the observed shortening of sarcomeres during contraction?

    <p>Arrangement of thin and thick filaments</p> Signup and view all the answers

    What constitutes the thin filaments in sarcomeres?

    <p>Actin, troponin, and tropomyosin</p> Signup and view all the answers

    What are kinesins and dyneins?

    <p>Motor proteins that move along microtubules</p> Signup and view all the answers

    What is the role of dyneins in intracellular movement?

    <p>Move cargo toward the minus ends of microtubules</p> Signup and view all the answers

    What is the function of myosins in cellular processes?

    <p>Exert force on actin microfilaments</p> Signup and view all the answers

    What causes cilia and flagella to bend, generating forces for movement?

    <p>Doublet sliding within the axoneme</p> Signup and view all the answers

    What is the primary responsibility of type II myosins?

    <p>Pulling arrays of actin filaments together, resulting in cell contraction</p> Signup and view all the answers

    What are skeletal muscles composed of?

    <p>Parallel muscle fibers responsible for voluntary movement</p> Signup and view all the answers

    What did Chargaff observe about the amount of nucleotides in DNA?

    <p>The amount of A = T and the amount of G = C</p> Signup and view all the answers

    What did Watson and Crick propose about the structure of DNA?

    <p>DNA is a double helix</p> Signup and view all the answers

    What was known about the bases in DNA at physiological pH?

    <p>They would be able to form hydrogen bonds with each other</p> Signup and view all the answers

    What did Erwin Chargaff study in DNA?

    <p>Base composition and relative amounts of the four bases</p> Signup and view all the answers

    What was Chargaff's most striking observation about the base composition of DNA?

    <p>The amount of A = T, and the amount of G = C</p> Signup and view all the answers

    What did Watson and Crick build to determine the structure of DNA?

    <p>Wire models</p> Signup and view all the answers

    What did Chargaff show about the DNA from different cells of a given species?

    <p>It has the same percentage of each of the four bases</p> Signup and view all the answers

    What is the significance of Chargaff's rules?

    <p>The significance was not understood until Watson and Crick proposed the double-helix model for DNA structure</p> Signup and view all the answers

    What did Chargaff's rules reveal about the nucleotide bases?

    <p>A = T and G = C</p> Signup and view all the answers

    What did Watson and Crick determine about the structure of DNA?

    <p>It had a sugar phosphate backbone with nitrogenous bases attached</p> Signup and view all the answers

    Who developed the double helix model of DNA?

    <p>Watson and Crick</p> Signup and view all the answers

    How many base pairs are there per helical turn in the double helix model of DNA?

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

    What is the distance per nucleotide pair in the double helix model of DNA?

    <p>0.34 nm</p> Signup and view all the answers

    What type of pairing adheres to Chargaff’s rules in DNA?

    <p>Purine-pyrimidine</p> Signup and view all the answers

    How is DNA length measured?

    <p>Base pairs (bp)</p> Signup and view all the answers

    What is the biological significance of Z-DNA?

    <p>Not fully understood</p> Signup and view all the answers

    What mediates the interconversion between relaxed and supercoiled forms of DNA?

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

    What induces strand separation (denaturation) in DNA?

    <p>Raising temperature or pH</p> Signup and view all the answers

    What is the challenge of DNA packaging in eukaryotes?

    <p>DNA interacts with histones to form chromatin</p> Signup and view all the answers

    What are plasmids in bacteria?

    <p>Small circular DNA molecules with genes for replication and cellular functions</p> Signup and view all the answers

    Study Notes

    Microtubules: Structure, Assembly, and Function

    • Microtubules (MTs) are the largest structural elements of the cytoskeleton, involved in various cell functions.
    • Two types of microtubules exist: cytoplasmic microtubules and their functions in maintaining axons, formation of spindles, and cell shape.
    • Tubulin heterodimers are the protein building blocks of microtubules, consisting of protofilaments with α and β-tubulin.
    • Protofilaments have inherent polarity with plus and minus ends, and microtubules form through reversible polymerization of tubulin dimers.
    • Microtubule assembly involves nucleation, elongation, and critical concentration of tubulin dimers.
    • Addition of tubulin dimers occurs more quickly at the plus ends of microtubules, leading to treadmilling.
    • GTP hydrolysis contributes to the dynamic instability of microtubules, involving GTP-tubulin and dynamic instability with catastrophe and rescue phases.
    • Microtubules originate from microtubule-organizing centers (MTOCs) and centrosomes containing γ-tubulin ring complexes (γ-TuRCs).
    • MTOCs organize and polarize microtubules within cells, nucleating and anchoring MTs with fixed polarity.
    • Microtubules facilitate various cellular functions, including maintaining cell shape and facilitating intracellular transport.
    • Microtubule-based drugs such as taxanes and vinca alkaloids target microtubule dynamics for cancer treatment.
    • Microtubule-associated proteins (MAPs) regulate microtubule dynamics and stability, influencing their functions in the cell.

    Cytoskeleton Proteins: Actin and Intermediate Filaments

    • Myosin subfragment 1 (S1) binds to actin microfilaments (MFs) in a distinctive arrowhead pattern
    • The plus end of microfilaments is called the barbed end, and the minus end is called the pointed end
    • Actin monomers in the cytosol bind ATP and are converted to ADP after complexing ATP
    • Microfilaments show polarity with more rapid addition or loss of G-actin at the plus end
    • Cells can dynamically assemble actin into various structures using actin-binding proteins
    • Thymosin β4 binds a large amount of free G-actin, while profilin competes for G-actin binding
    • ADF/cofilin binds ADP-G-actin and F-actin to increase turnover of ADP-actin at the minus end
    • Capping proteins like CapZ and tropomodulins regulate the growth of microfilaments
    • Filamin is important in forming loose networks of crosslinked actin filaments
    • Actin may be bundled by proteins like α-actinin and fascin into highly organized arrays
    • Microfilaments are connected to the plasma membrane by crosslinks made of myosin I and calmodulin
    • Actin can form a dendritic network through the Arp2/3 complex, activated by proteins like WASP and WAVE/Scar

    Microtubule and Microfilament-Based Intracellular Movement

    • Microtubules act as tracks for organelle and vesicle transport inside cells
    • Kinesins and dyneins are motor proteins that move along microtubules
    • Kinesins move toward the plus ends of microtubules and are involved in fast axonal transport
    • Dyneins move cargo toward the minus ends of microtubules and are linked to cargo by dynactin protein complexes
    • Microtubule motors are crucial for shaping the endomembrane system and transporting vesicles
    • Cilia and flagella are involved in cellular movement and consist of axoneme connected to a basal body
    • Doublet sliding within the axoneme causes cilia and flagella to bend, generating forces for movement
    • Myosins, a large superfamily of ATP-dependent motors, interact with and exert force on actin microfilaments
    • Myosins function in muscle contraction, cell movement, phagocytosis, and vesicle transport
    • Type II myosins are well understood and responsible for pulling arrays of actin filaments together, resulting in cell contraction
    • Muscle contraction is a familiar example of mechanical work mediated by intracellular filaments
    • Skeletal muscles are composed of parallel muscle fibers responsible for voluntary movement

    DNA Structure and Packaging

    • The double helix model of DNA was developed by Watson and Crick, with critical evidence from X-ray diffraction data by Rosalind Franklin
    • The model revealed 10 base pairs per helical turn and a 0.34 nm distance per nucleotide pair
    • Purine-pyrimidine pairing adheres to Chargaff’s rules, with hydrogen bonding between complementary bases (adenine-thymine, guanine-cytosine)
    • The double helix model suggested a mechanism for DNA replication, where the strands could act as templates for new complementary strands
    • DNA length is measured in base pairs (bp), with larger stretches in kilobases (kb)
    • DNA can form right-handed (BDNA) and left-handed (Z-DNA) helices, with Z-DNA's biological significance not fully understood
    • DNA can be interconverted between relaxed and supercoiled forms, with positive and negative supercoils
    • Supercoiling occurs in both linear and circular DNA, mediated by topoisomerases which induce and relax supercoils
    • Strand separation (denaturation) can be induced by raising temperature or pH, while reformation (renaturation) occurs by lowering the temperature to permit hydrogen bonds to reform
    • DNA packaging is a challenge for all forms of life, especially in eukaryotes where DNA interacts with histones to form chromatin
    • Bacterial chromosomes are bound to proteins, negatively supercoiled, and folded into loops held in place by RNAs and proteins
    • Bacteria may contain plasmids, small circular DNA molecules with genes for replication and cellular functions, including virulence factors and metabolic enzymes.

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    Description

    Test your knowledge of microtubules with this quiz on their structure, assembly, and functions. Explore topics such as tubulin heterodimers, microtubule nucleation, GTP hydrolysis, and the role of microtubules in maintaining cell shape and facilitating intracellular transport. Also, discover how microtubule-based drugs are used in cancer treatment and the influence of microtubule-associated proteins on their dynamics and stability.

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