WBR0747

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Cardiology, SubCategory::Musculoskeletal/Rheumatology
Prompt	[[Prompt::A researcher is studying the role of troponin on muscle contraction. His experiment demonstrates that the general physiology of muscle contraction in both cardiac and skeletal muscles is identical. Nonetheless, he describes a specific discrepancy between both phenomena. Which of the following is true when comparing cardiac to skeletal muscle physiology?]]
Answer A	AnswerA::The form of energy required for contraction of skeletal muscle cells is ATP, whereas the form of energy required for contraction of cardiac muscle cells is GTP
Answer A Explanation	AnswerAExp::Both cardiac and skeletal muscle cells use ATP to drive contraction.
Answer B	AnswerB::Cardiac troponin contains more amino acids than skeletal muscle troponin
Answer B Explanation	AnswerBExp::Cardiac troponin contains 33 additional amino acids compared with skeletal troponin.
Answer C	AnswerC::Cardiac troponin undergoes acetylation, while skeletal muscle troponin undergoes phosphorylation
Answer C Explanation	AnswerCExp::Troponin of both cardiac and skeletal muscle cells undergoes phosphorylation.
Answer D	AnswerD::Calcium is a co-factor required for skeletal muscle contraction but not for cardiac muscle contraction
Answer D Explanation	AnswerDExp::Calcium is required by troponin for both skeletal and cardiac muscle cells.
Answer E	AnswerE::The troponin-tropomyosin complex is present in skeletal muscle cells but is absent in cardiac muscle cells
Answer E Explanation	AnswerEExp::The troponin-tropomyosin complex is present in both skeletal and cardiac muscle cells.
Right Answer	RightAnswer::B
Explanation	[[Explanation::In contrast to skeletal troponin, cardiac troponin contains more amino acids. There are approximately 33 additional amino acids found in cardiac troponin. The extra number of amino acids are located at the N-terminus. These additional amino acids are most significant for the presence of 2 adjacent serine residues that are phosphorylated by protein kinase A when cardiac cells are stimulated by beta-agonists. Educational Objective: Cardiac troponin contains 33 additional amino acids compared to skeletal troponin. These additional amino acids are most significant for the presence of 2 adjacent serine residues that are phosphorylated by protein kinase A when cardiac cells are stimulated by beta-agonists. References: Zhang R, Zhao J, Mandveno A, Potter J. Cardiac troponin I phosphorylation increases the rate of cardiac muscle relaxation. 1995;76:1028-1035. First Aid 2014 page 217]]
Approved	Approved::Yes
Keyword	WBRKeyword::Cardiac, WBRKeyword::Troponin, WBRKeyword::Amino acid, WBRKeyword::Serine residue, WBRKeyword::Serine residues, WBRKeyword::Amino acids, WBRKeyword::Amino, WBRKeyword::Acid, WBRKeyword::Acids, WBRKeyword::Serine, WBRKeyword::Beta agonist, WBRKeyword::Beta-agonist, WBRKeyword::Muscle contraction, WBRKeyword::Cardiac troponin, WBRKeyword::Skeletal troponin, WBRKeyword::Residue, WBRKeyword::Residues, WBRKeyword::Beta, WBRKeyword::Agonist, WBRKeyword::Muscle, WBRKeyword::Contraction, WBRKeyword::Skeletal, WBRKeyword::Cardiac
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