Explain why the phenotypes associated with the human FXN gene can be studied in a mouse cell. Unlike skeletal muscle cells, heart muscle cells cannot rely on fermentation for long. Explain the inability of heart muscle cells to function using only fermentation for metabolism. ATP acts as a negative feedback regulator of phosphofructokinase, one of the enzymes in glycolysis. Predict the eventual effect of ATP on pyruvate production in heart cells that express excess amounts of the normal frataxin.

Heart muscles have long refractory period.

Explanation:

Heart muscle cells cannot rely on fermentation for long period of time because heart muscles have long refractory period which does not allow it to use the fermentation process. They have rich blood supply and have capillary density 4 times more than normal skeletal muscles. The anaerobic capacity is limited in the heart which does not allow the heart muscle cells to use fermentation process for metabolism. Our heart requires oxygen in large amount and very quickly for ATP production.

i don't know. if i were you, i would search it up online : d

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?