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?

The question is incomplete, it lacks options. The options are:

A) Actin

B) Myosin

C) Acetylcholine

D) Tropomyosin

E) Troponin

The correct answer is (E)Troponin

Explanation:

Actin and myosin are proteinous filaments responsible for the force that drives the muscular system. These two proteins need to interact in order to generate this force. Here comes the role of a third protein called TROPONIN.

Troponin is a protein that plays a vital role in muscular contraction. It is a complex made up of Troponin I, C and T which binds to calcium ions that triggers a change, bringing about contraction in muscles.

What really occurs when calcium ions from the sarcoplasmic reticulum bind to the troponin complex is that the complex of troponin changes its conformation, causing tropomysin (a protein that regulates the binding of myosin to actin by covering the binding site in a relaxed muscle state) to shift from the binding sites of myosin located on ACTIN. This allows myosin to bind to actin forming a cross-bridge. This triggers muscle contraction necessary for breathing.

However, if troponin is defective due to a change (mutation) that has occurred in the gene that encodes it, the process of bringing about contraction will not be possible, which will lead to inability to breathe and subsequently death. This is the case of the new born baby.

the correct answer is d