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#myosin

14 public questions tagged with this topic.

ZOOLOGY

Which muscle protein forms the thick filaments in the sarcomere?

Myosin forms thick filaments and plays a crucial role in muscle contraction. This follows from latest NCERT 2026-27 principle explaining the concept clearly for NEET students in simple steps as per rationalized syllabus.

Ref: NCERT Biology Textbook - Latest Edition for Academic Session 2026-27 (Zoology section, Rationalized Textbook for Class XI and XII), Chapter: Biology - Zoology portion (Latest NCERT Textbooks for Academic Session 2026-27 - Rationalized Edition for Class XI and XII), Topic: Structural organization, ph

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Cytoskeleton

Which statement is TRUE about myosin and muscle contraction?

Among eighteen myosin classes class II myosins dominate muscle mechanics due to capacity to assemble into higher order structures essential for force scaling. Each myosin II molecule comprises two heavy chains with N terminal motor domains hydrolyzing ATP IQ motifs binding essential and regulatory light chains forming lever and C terminal extended coiled coil driving dimerization plus further self association into filaments. In skeletal muscle dimers polymerize antiparallel into 1.6 micron long thick filaments containing about 300 molecules bare zone in middle heads projecting helically outwar

Ref: Lodish et al., Molecular Cell Biology, Chapter 18 – Myosin II major myosin of muscle thick filaments.

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Cytoskeleton

Which type of myosin is primarily involved in non-muscle cell contractility?

Non muscle contractility underpins stress fiber maintenance, adhesion maturation, morphogenesis and wound closure, distinct from skeletal muscle sarcomeres employing troponin regulation. Myosin II family in non muscle cells includes isoforms IIA, IIB and IIC sharing hexameric composition two heavy chains plus essential and regulatory light chains, forming short bipolar filaments that transiently associate with actin rather than stable thick filaments. Activation occurs via phosphorylation of 20 kilodalton regulatory light chain RLC at Ser19 by calcium calmodulin dependent MLCK and Rho associat

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 18: Nonmuscle Myosin II in Contractility.

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Cytoskeleton

What happens when ATP is hydrolyzed by myosin in the actin-myosin cycle?

Actomyosin ATPase cycle illustrates chemomechanical coupling. Starting rigor actin myosin complex with empty nucleotide pocket tightly bound, ATP binding induces opening of actin binding cleft and dissociation rate 1000 per second. Free myosin closes Switch I Switch II around gamma phosphate hydrolyzing ATP to ADP inorganic phosphate with rate 50 per second, coupled to recovery stroke where lever arm swung 90 degrees from post stroke to pre stroke position, converter domain rotation storing elastic energy, myosin primed high energy configuration. This hydrolysis induced conformational change e

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Myosin ATP Hydrolysis and Conformational Change.

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Cytoskeleton

The major function of titin in muscle contraction is to:

Massive protein titin, encoded by TTN gene 363 exons, 38,138 residues in canonical cardiac isoform N2B 3.8 megadalton, spans half sarcomere from Z disc to M line, single molecule. N terminal Z disc anchor binds alpha actinin via Z repeats 1 to 7 and telethonin T cap forming antiparallel complex, I band extensible region contains tandem immunoglobulin like domains Ig 80 repeats that unfold at low force providing entropic elasticity, PEVK region rich in proline glutamate valine lysine behaving as worm like chain, and cardiac specific N2B element with spring properties. A band region with FN3 and

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17: Titin Elasticity and Myosin Binding.

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Cytoskeleton

Which of the following determines the speed of myosin movement along actin filaments?

Mechanistic model of myosin step size explains velocity differences among isoforms. Lever arm hypothesis states small conformational change of converter domain upon phosphate release rotation about 10 degrees amplified by rigid lever arm helical neck decorated with IQ motifs bound to light chains acting as fulcrum. Step size roughly equals lever length times angular change, so each IQ motif about 5 to 6 nanometer contributes. Constructing chimeras fusing artificial alpha actinin repeats or duplicating IQ motifs increased sliding speed linearly in motility assays without altering ATPase kcat, c

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Lever Arm Length and Myosin Speed.

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Cytoskeleton

The power stroke in the actin-myosin cycle occurs due to:

Cross bridge cycle parsed by transient kinetics reveals distinct substeps responsible for detachment priming and force generation. Myosin rigor complex actin myosin no nucleotide strongly bound. ATP binding rate 1 to 3 per micromolar per second causes rapid dissociation 500 to 1000 per second. Detached myosin hydrolyzes ATP to ADP plus inorganic phosphate rate about 50 per second inducing recovery stroke moving lever arm into pre power stroke high energy conformation approximately 90 degree rotation storing strain. Myosin ADP Pi weakly binds actin via electrostatic contacts. Isomerization into

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 18: Power Stroke and Phosphate Release Mechanism.

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Cytoskeleton

Which myosin type is responsible for intracellular cargo transport?

Intracellular cargo trafficking covers both microtubule and actin routes. Long range 10 to 100 micron interphase transport uses kinesin dynein on microtubules, while short range local transport within cortical actin rich zones 1 to 10 micron uses myosin. Processive myosin capable of multiple steps without dissociation required for efficient transport. Myosin V class features high duty ratio spending about 70 percent cycle strongly attached, dimeric coiled coil tail, six IQ motifs with calmodulin light chains per head forming long 24 nanometer lever arm achieving 36 nanometer step matching heli

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17: Myosin V and Cargo Transport.

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Cytoskeleton

Actin filaments interact with which motor protein for intracellular transport?

Two distinct superfamilies of cytoskeletal motors evolved to walk along filaments using ATP hydrolysis. Myosin motors share N terminal head motor domain containing actin binding interface including helix turn helix, cardiomyopathy loop, P loop ATPase, Switch I II for gamma phosphate sensing and lever arm with IQ motifs binding calmodulin light chains. Upon interaction with F actin 7 nanometer helical filament, head undergoes conformational cycle releasing phosphate driving swing of lever arm producing force along filament. Diverse isoforms specialize: myosin II non processive forming bipolar f

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Myosin Motors and Actin Filaments.

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