Questions and Answers
What are the two main movements performed by a cilium?
How long does each ciliary movement cycle typically take?
What distinguishes flagella from cilia in terms of movement?
What is the arrangement of microtubules in a cilium?
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What is the primary force generated by the ciliary movement?
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What provides support for human red blood cells to maintain their discoid shape?
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Which process is essential for cell crawling?
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What role does actin play during the cell crawling process?
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What happens at the rear of the cell during cell crawling?
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How do cells establish new anchorage points during movement?
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What occurs after a cell drags itself forward during crawling?
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What term best describes the leading edge of the cell during movement?
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What is the primary function of spectrin in red blood cells?
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What is the term used to describe the switching back and forth between polymerization and depolymerization of microtubules?
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What controls the dynamic instability of microtubules?
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What happens when tubulin dimers hydrolyze their GTP to GDP?
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How does a microtubule maintain stability during growth?
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Why are tubulin dimers carrying GTP more conducive to microtubule growth than those carrying GDP?
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What occurs during the process known as dynamic instability?
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What is the consequence of losing the GTP cap on a microtubule?
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What enables a new microtubule to grow if an existing one disappears?
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What role do actin-binding proteins play in cell crawling?
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What is the function of the head domain of Myosin-I?
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How do myosin-II molecules interact to form a bipolar myosin filament?
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What characterizes the arrangement of myosin heads in a myosin filament?
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What does the process of muscle contraction depend on?
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Which feature is specific to Myosin-I across all cell types?
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What does the movement of the head group of Myosin-I toward the plus end of the actin filament achieve?
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What type of structure does muscle myosin form?
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What triggers muscle contraction in the cells?
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What happens to Ca2+ levels when the nerve signal terminates?
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What role do troponin and tropomyosin play during muscle contraction?
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How does smooth muscle activation differ from skeletal muscle activation?
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Where is smooth muscle predominantly found?
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What occurs to tropomyosin during muscle contraction?
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What is a characteristic of the contraction mechanism in smooth muscle?
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What initiates the reconfiguration of troponin and tropomyosin after contraction?
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Study Notes
Microtubules and Dynamic Instability
- Microtubules exhibit dynamic instability, rapidly switching between growth and shrinkage by losing tubulin dimers from their plus ends.
- A microtubule can disappear and be replaced by a new one growing from the γ-tubulin ring complex.
- Stabilization of a microtubule's plus end through attachment to other structures prevents its disassembly and links distant cell regions to the centrosome.
GTP Hydrolysis and Microtubule Dynamics
- Microtubule dynamic instability is driven by GTP hydrolysis inherent to tubulin dimers.
- Tubulin dimers with bound GTP (red) bind more tightly than those with GDP (dark green), promoting growth at the plus ends.
- Loss of the GTP cap due to slow growth can result in the microtubule shrinking as GDP-carrying dimers are less tightly bound.
Cilia and Flagella Movement
- Cilia and flagella contain stable microtubules, typically powered by dynein, differing from cytoplasmic microtubules in arrangement.
- Cilia perform a rapid power stroke followed by a slower recovery stroke, generating movement across cell surfaces in cycles of 0.1–0.2 seconds.
- Flagella are longer than cilia and propel entire cells, creating wave-like movements.
Actin Filaments and Cell Movement
- Cortical actin filaments support the plasma membrane in eukaryotic cells, notably in human red blood cells, maintaining their shape.
- Cell crawling relies on coordinated processes: protrusion at the leading edge, adhesion to the substrate, and forward movement via traction.
- Actin polymerization at the leading edge drives membrane movement and new attachment points form while the rear contracts via myosin action.
Myosin Interaction with Actin
- Myosin-I is universal in cells, with a head domain binding to actin filaments, enabling vesicle movement or shape alteration through the plasma membrane.
- Myosin-II forms bipolar filaments with heads that project outward, allowing for interaction with actin during muscle contraction.
Muscle Contraction Mechanism
- Muscle contraction is triggered by a sudden rise in cytosolic Ca2+, leading to simultaneous contraction of myofibrils across the cell.
- Rapid Ca2+ uptake by the sarcoplasmic reticulum stops contraction when Ca2+ levels decrease, repositioning troponin and tropomyosin to block myosin-actin binding.
Smooth Muscle Cell Functionality
- Smooth muscle cells, involved in involuntary contractions of organs like the stomach and blood vessels, activate myosin through slow signaling mechanisms.
- This activation can occur via various extracellular signals—such as adrenaline and serotonin—allowing for sustained contractions over time.
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Description
Test your understanding of microtubules, their dynamic instability, and the mechanisms involved in their growth and shrinkage. This quiz covers aspects of GTP hydrolysis and the role of microtubules in cilia and flagella movement. Prepare to explore the intricate world of cellular structures!
