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Questions and Answers
Which of the following is NOT one of the three types of protein filaments that make up the cytoskeleton?
What are intermediate filaments primarily composed of?
Which structure disassembles and reforms during each cell division?
Which phosphorylation process controls the disassembly of the nuclear lamina?
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What is the structural composition of microtubules?
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Where is the minus end of microtubules embedded in animal cells?
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What is the major microtubule-organizing center in animal cells?
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What drives the dynamic instability of microtubules?
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What prevents a microtubule from disassembling when stabilized?
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Which motor protein moves toward the plus end of microtubules?
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Which motor protein moves toward the minus end of microtubules?
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What structure contains a '9 + 2' arrangement of microtubules?
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What generates the sliding force that causes bending in cilia and flagella?
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What is the function of myosin-I in cells?
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Which actin-binding protein promotes actin polymerization at the leading edge of crawling cells?
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What mechanism allows actin filaments to undergo 'treadmilling'?
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Where are the plus ends of actin filaments attached in muscle cells?
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What triggers muscle contraction?
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What type of myosin is involved in muscle contraction?
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What is the primary function of intermediate filaments?
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Which of the following structures is associated with intermediate filaments?
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What causes microtubules to shrink during dynamic instability?
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Which protein is involved in actin-based muscle contraction?
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What is the role of Ca2+ in muscle contraction?
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Which structure is responsible for organizing the internal layout of a cell?
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Which class of intermediate filaments is found in nerve cells?
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What helps stabilize actin filaments in the intestinal microvilli?
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Which molecule binds and hydrolyzes ATP during muscle contraction?
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What forms the core of cilia and flagella?
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What component of the cytoskeleton allows the cell to crawl?
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Where are actin filaments most densely concentrated in a cell?
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Which motor protein is involved in vesicle transport along actin filaments?
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How is the dynamic instability of microtubules regulated?
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What structure is responsible for muscle fiber contraction?
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What happens when GTP is hydrolyzed to GDP in microtubules?
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Which of the following processes involves actin polymerization?
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What process is responsible for shortening the sarcomere during muscle contraction?
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Which of the following is involved in the formation of the contractile ring during cell division?
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What triggers the release of Ca2+ from the sarcoplasmic reticulum in muscle cells?
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In which part of the cell does actin associate with myosin-I to change the shape of the plasma membrane?
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What happens to the muscle when Ca2+ is rapidly pumped back into the sarcoplasmic reticulum?
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Which structure organizes microtubules during mitosis in animal cells?
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What allows microtubules to grow from the centrosome?
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What type of actin-based structure is found in crawling cells?
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Which structure is stabilized by proteins to prevent the disassembly of actin filaments?
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What structure contains actin filaments and spectrin in red blood cells?
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What is the role of tropomyosin in muscle cells?
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What structure is responsible for the rhythmic beating of cilia and flagella?
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Which protein acts as a molecular switch to initiate muscle contraction upon binding Ca2+?
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Study Notes
Cytoskeleton Components
- Cytoskeleton consists of three main types of protein filaments: intermediate filaments, microtubules, and actin filaments. Collagen fibers are not part of the cytoskeleton.
- Intermediate filaments are primarily composed of fibrous proteins featuring an α-helical rod domain, providing structural stability.
- Microtubules are made up of 13 parallel protofilaments composed of tubulin dimers, facilitating cellular organization and transport.
Microtubule Dynamics
- Microtubules disassemble and reform during cell division, with their minus ends embedded in the centrosome, the major microtubule-organizing center in animal cells.
- Dynamic instability of microtubules is driven by GTP hydrolysis, where rapid GTP hydrolysis causes shrinkage if dimer addition is slower than hydrolysis.
- When stabilized, microtubules resist disassembly through attachment to cellular structures or proteins.
Motor Proteins and Movement
- Kinesin moves toward the plus end of microtubules, while dynein moves toward the minus end, facilitating intracellular transport.
- Motor proteins like myosin-I transport vesicles along actin filaments, while myosin-II is involved in muscle contraction.
- Dyneins create bending forces in cilia and flagella, essential for their movement.
Actin Filament Functionality
- Actin filaments undergo "treadmilling," where ATP hydrolysis at the minus end occurs while monomers are added at the plus end, allowing dynamic cellular shape changes.
- In muscle cells, actin filaments are concentrated at the Z-disc and interact with myosin in contraction mechanisms.
- Myosin-I plays a role in cell movement by binding with actin and facilitating vesicle transport.
Muscle Contraction Mechanism
- Muscle contraction is triggered by the release of Ca2+ from the sarcoplasmic reticulum, prompting interaction between actin and myosin.
- Myosin-II, the type of myosin involved in contraction, hydrolyzes ATP, fueling movement.
- Tropomyosin regulates muscle contraction by blocking myosin-binding sites on actin, and is stabilized by binding proteins to prevent disassembly in microvilli.
Cell Movement and Structure
- The actin cortex allows cells to crawl, with structures like lamellipodia aiding in movement.
- Intermediate filaments provide mechanical resilience, especially in nerve cells (neurofilaments) and around the nuclear lamina.
- The organization of the cytoskeleton is vital for cellular internal layout, and the stability of actin involves proteins such as spectrin.
Ca2+ Role in Muscular Function
- Ca2+ binds to troponin, initiating muscle contraction by allowing myosin-actin interaction, resulting in sliding of actin past myosin to shorten sarcomeres.
- Ca2+ rapidly pumped back into the sarcoplasmic reticulum leads to muscle relaxation.
Additional Key Structures
- Cilia and flagella feature a "9 + 2" microtubule arrangement, essential for their motility.
- The γ-tubulin ring complex provides a platform for microtubule growth from the centrosome.
- Muscular structures like sarcomeres and myofibrils are responsible for contraction, with the sarcoplasmic reticulum acting as calcium storage.
Summary of Processes
- Cilia and flagella movement is driven by dynein, and muscle contraction is a coordinated event involving actin polymerization and interaction with myosin.
- Dynamic instability and treadmilling of actin and microtubules are fundamental processes regulating cell shape and movement, with motor proteins facilitating intracellular transport.
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Description
Test your knowledge on the components and functions of the cytoskeleton in cell biology. This quiz covers protein filaments, their structures, and their roles during cell division. Dive deep into the world of cytoskeletal elements and enhance your understanding of cellular structures.
