This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: miscellaneous, Subject name: Biochemistry
[{'content': 'All the following are features of Cardiac muscle Except \nSelect and explain. \nA. Striated, B. Large T tubules, C. Troponin system present, D. Caldesmon is impoant regulatory protein', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Some Differences among Skeletal, Cardiac, and Smooth MuscleNoSkeletal MuscleCardiac MuscleSmooth Muscle1StriatedStriatedNonstriated2No syncytiumSyncytialSyncytial3Small T tubulesLarge T tubulesGenerally rudimentary T tubules4Sarcoplasmic reticulum well developed andCa2+ pump acts rapidlySarcoplasmic reticulum present andCa2+ pump acts relatively rapidlySarcoplasmic reticulum often rudimentaryand Ca2+ pump acts slowly5Plasmalemma contains few hormonesreceptorsPlasmalemma contains a variety ofreceptors (eg, a- and b-adrenergic)Plasmalemma contains a variety ofreceptors (eg, a- and b-adrenergic)6Nerve impulse initiates contractionHas intrinsic rhythmicityContraction initiated by nerve impulses,hormones, etc7Extracellular fluid Ca2+ not impoant forcontractionExtracellular fluid Ca2+ impoant forcontractionExtracellular fluid Ca2+ impoant forcontraction8Troponin system presentTroponin system presentLacks troponin system; uses regulatoryhead of the myosin9Caldesmon not involvedCaldesmon not involvedCaldesmon is impoant regulatory protein10Very rapid cycling of the cross-bridgesRelatively rapid cycling of the cross bridgesSlow cycling of the cross-bridges permitsslow, prolonged contraction and lessutilization of ATPRef: Harper&;s Biochemistry; 30th edition; Chapter 51; Muscle & the cytoskeleton; Table 51-3', 'role': 'assistant'}]