What might happen if skeletal muscle lacked tropomyosin?   A. The striation pattern would disappear.   B. Ca2+ levels in the muscle would decrease.   C. Actin and myosin would not be able to form cross-bridges.   D. Acetylcholine would not be released into the synaptic cleft.   E. Myosin and actin would form cross-bridges whenever ATP is available.

What happens when myosin filaments hydrolyze ATP molecules in muscles?    a. Actin–myosin complexes dissociate, leading to muscle contraction.   b. Actin–myosin complexes dissociate, leading to muscle relaxation.   c. Actin–myosin complexes are formed, leading to muscle contraction.   d. Actin–myosin complexes are formed, leading to muscle relaxation.

Which of the following is a microscopic feature of a skeletal muscle fiber? a. It contains multiple nuclei that are centrally located b. it contains myoglobin for oxygen storage c. it contains glycosomes for glycogen storage d. a and b e. b and c

Which is most accurate with regard to the phrase "muscle fiber"? A. Muscle fibers technically only refer to actin protein filaments B. muscle fibers are often called "cells" but actually they are many cells fused into a long tubular structure. C. muscle fibers are also called fascicles which are bundles of many muscle cells D. Muscle fibers are the same as myofibril organelles, packed into each cell

Which statement CORRECTLY describes a motor unit? O a. A single muscle fibre plus all the motor neurons that innervate it. O b. All the motor neurons supplying a single muscle O c. A pair of antagonistic muscles O d. A single motor neuron plus all the muscle fibres it innervates

In what type of muscle would the structure illustrated in the image at right be found? A. The flight muscle of a bumblebee B. The longitudinal muscles underlying the cuticle in C. elegans C. The longitudinal muscles of the vertebrate intestine D. The cardiac muscle of mammals E. None of the above actin filament Dense body Relaxed myosin filament Contracted

Match the ATP duty of myosin to its description                                                             ATP binding                                                             ATP hydrolysis                                                             Pi release                                                             ADP release A. myosin releases actin, cross-bridge dissociation, step in cycle that is interrupted at death, the molecular basis of rigor mortis B. conformation change causing power stroke  C. cocking of the motor domain, high-energy conformation  D. binding of myosin to actin, improved by drug which led to increased cardiac output

Which of the following statements about skeletal muscle is CORRECT? Select one: a. An increase in Na+ concentration in the cytosol starts muscle filament sliding. b. The muscle is non-striated and involuntary. c. The muscle is involved in shivering thermogenesis. d. The muscle contracts in response to parasympathetic stimulation. e. The muscle contracts in response to hormones.

Which statement about striated skeletal muscle is true?   A. The tension generated by a muscle is invariable.   B. Mechanical summation of twitches in a muscle fiber leads to a graded increase in the tension that is above that generated by a single twitch.   C. A single action potential arriving at the neuromuscular junction is not sufficient to cause a muscle fiber to twitch.   D. Muscle twitches are able to mechanically sum when Ca2+ is quickly and completely removed from the sarcoplasm between action potentials.   E. An action potential in the muscle cell activates contraction by releasing Na+ into the sarcoplasm.

You know from experience that skeletal muscle tires quite quickly, especially if there is not enough oxygen. Interestingly, shellfish such as clams can maintain a month-long contraction in the muscle that keeps the shell closed. No oxygen gets in this situation. These muscles have a different version of myosin called paramyosin. Knowing what you know about the cellular mechanism of muscle contraction, propose a hypothesis to explain how paramyosin might work.