WBR0747

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
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 shows that the general physiology of muscle contraction in both cardiac and skeletal muscles is the same. Nonetheless, he describes a discrepancy between both phenomena. Which of the following is true when comparing cardiac vs. 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 more amino acids,
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::Cardiac troponin contains more amino acids as compared to that of skeletal troponin. 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 cell troponin contain more amino acids than skeletal muscle troponin. Reference: Zhang R, Zhao J, Mandveno A, Potter J. Cardiac troponin I phosphorylation increases the rate of cardiac muscle relaxation. 1995; 76:1028-1035. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::cardiac, WBRKeyword::troponin, WBRKeyword::extra, WBRKeyword::amino, WBRKeyword::acid, WBRKeyword::acids, WBRKeyword::serine, WBRKeyword::residue, WBRKeyword::residues, WBRKeyword::beta, WBRKeyword::agonist, WBRKeyword::stimulation, WBRKeyword::muscle, WBRKeyword::contraction, WBRKeyword::skeletal, WBRKeyword::cardiac
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::