Question

the hormone melatonin regulates many physiological processes in vertebrates. melatonin is synthesized by a gland in the brain, and it is carried by the bloodstream to different cells throughout the body. the effects of melatonin depend on the type of cell it is received by. melatonin affects the process of bone remodeling, which renews the adult skeleton. this process is partly regulated by the actions of a type of bone cell called osteoblasts. the melatonin receptor, mt2, is a membrane protein found in cells such as osteoblasts. when the mt2 receptor is bound by melatonin, it directs a change in the activity of osteoblasts. a comparison of bone mass over six weeks in mice with functioning and non - functioning versions of the mt2 receptor revealed the following: mt2 protein|increase in bone mass normal|11.1% non - functioning|8.3% which of the following best explains the results? a. a mutation in the gene encoding mt2 produced a non - functioning protein, which altered the function of a specialized cell and decreased the ability of the mice to produce new bone. b. osteoblasts that have abnormalities in the structure of the mt2 protein were more effective in synthesizing the melatonin needed to make new bone. c. osteoblasts that have abnormalities in the structure of the mt2 protein did not respond to melatonin, and this impacted the function of the cell but did not have an effect on the organism. d. a mutation in the gene encoding mt2 disrupted the ability of some cells to respond to melatonin, but these changes did not affect the function of osteoblasts.

Explanation:

The table shows that when the MT2 protein is non - functioning, the increase in bone mass is lower compared to when it is normal. A mutation in the gene encoding MT2 can produce a non - functioning protein. This non - functioning protein would alter the function of osteoblasts (specialized cells involved in bone remodeling), resulting in a decreased ability to produce new bone, which is consistent with the lower increase in bone mass seen in non - functioning MT2 cases. Option B is incorrect as abnormal MT2 proteins should not be more effective in synthesizing melatonin for new bone. Option C is wrong because it does affect the organism as seen by the change in bone mass. Option D is incorrect as it does affect the function of osteoblasts as evidenced by the bone mass change.

Answer:

A. A mutation in the gene encoding MT2 produced a non - functioning protein, which altered the function of a specialized cell and decreased the ability of the mice to produce new bone.