A newborn baby dies soon after birth because her diaphragm and rib cage muscles failed to contract and she was unable to breathe on her own. Examination of the baby’s DNA revealed that she had a genetic mutation in a gene that encoded a calcium-binding protein. Which protein was most likely defective in the baby?

Question

A.  actin
B.  myosin
C.  acetylcholine
D.  tropomyosin
E.  troponin

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

Gather Content
· What do you know about the proteins the bind to calcium in a muscle contraction? What other information is related to the question?

Choose Answer
· Given what you now know, what information is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

E.  troponin

Clarify Question
· What is the key concept addressed by the question?
        o The question asks about the proteins the bind to calcium in a muscle contraction.
· What type of thinking is required?
        o You are being asked to apply your knowledge about that proteins the bind to calcium in a muscle contraction.

Gather Content
· What do you know about the proteins the bind to calcium in a muscle contraction? What other information is related to the question?
        o When a nerve signal reaches a muscle the neurotransmitter, acetylcholine, is released at a neuromuscular junction and then binds to acetylcholine receptors that, in turn, open Na+ channels. This causes the muscle cell membrane to depolarize. This depolarization is conducted along the muscle cell membrane and down the transverse tubules to stimulate the release of Ca2+ from the sarcoplasmic reticulum. Ca2+ diffuses through the cytoplasm to myofibrils, causing contraction. When the muscle is at rest, a long filament of the protein tropomyosin blocks the myosin-binding sites on the actin molecule. Because myosin is unable to form cross-bridges with actin at these sites, muscle contraction cannot occur. When Ca2+ binds to another protein, troponin, the Ca2+–troponin complex displaces tropomyosin and exposes the myosin-binding sites on actin, permitting cross-bridges to form and contraction to occur.

Choose Answer
· Given what you now know, what information is most likely to produce the correct answer?
        o When troponin binds to Ca2+ it can displace tropomyosin, allowing actin and myosin to bind and form cross bridges. Actin, myosin, tropomyosin, and acetylcholine do not bind calcium so the mutation cannot be in these proteins.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to apply your knowledge about the proteins that bind to calcium in a muscle contraction. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you think that actin, myosin, tropomyosin, or acetylcholine bind calcium? Did you think that a lack of troponin binding to calcium would not block muscle contraction?