The protein that acts as a calcium receptor in skeletal muscle is:
Actin
Tropomyosin
Titin
Troponin
Dystrophin
The Correct Answer is D
Choice A reason: Actin is a structural protein that forms the thin filaments in muscle fibers. While it interacts with myosin during contraction, it does not bind calcium directly.
Choice B reason: Tropomyosin is a regulatory protein that blocks the myosin-binding sites on actin in a resting muscle. It shifts position when calcium binds to troponin but does not itself bind calcium.
Choice C reason: Titin is a large elastic protein that helps maintain the structural integrity of the sarcomere and contributes to passive elasticity. It does not function as a calcium receptor.
Choice D reason: Troponin is the correct answer. It is a regulatory protein complex associated with the thin filament. When calcium ions bind to troponin, it induces a conformational change that moves tropomyosin away from actin’s binding sites, allowing muscle contraction to occur.
Choice E reason: Dystrophin is a structural protein that connects the cytoskeleton of muscle fibers to the extracellular matrix. It is important for muscle integrity but does not bind calcium.
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Related Questions
Correct Answer is E
Explanation
Choice A reason: The scapula is part of the appendicular skeleton, not the axial skeleton. Therefore, this combination is incorrect.
Choice B reason: The pelvis includes both axial and appendicular components, but the pelvic girdle is considered part of the appendicular skeleton. This makes the answer inaccurate.
Choice C reason: Both the pectoral and pelvic girdles are part of the appendicular skeleton. Including them in the axial skeleton is incorrect.
Choice D reason: Arms, legs, hands, and feet are all part of the appendicular skeleton. They are not included in the axial skeleton.
Choice E reason: This is the correct answer. The axial skeleton consists of the skull, vertebral column, and rib cage. These structures form the central axis of the body and protect vital organs such as the brain, spinal cord, and thoracic organs.
Correct Answer is A
Explanation
Choice A reason: Scoliosis is the correct answer. It is characterized by a lateral curvature of the spine, often diagnosed in adolescence. It can range from mild to severe and may require bracing or surgery depending on progression.
Choice B reason: Lordosis refers to an exaggerated inward curvature of the lumbar spine. It is a spinal deformity but not the most common.
Choice C reason: Kyphosis is an exaggerated outward curvature of the thoracic spine, leading to a hunched posture. It is less common than scoliosis.
Choice D reason: Osteosis is not a recognized spinal deformity. It may be a misused or fictional term.
Choice E reason: A slipped disc, or herniated disc, involves displacement of intervertebral disc material. It causes pain and nerve compression but is not classified as a spinal deformity.
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