What are some examples of how energy is used in metabolic pathways?
they use the stored energy.
there are three ways (of which i know this is not an exhaustive list ) in which the energy is stored
ATP stored in phosphate group
GTP stored in phosphate group
NADH/FAD stored in by getting oxidized
these molecules are used during various process. what is interesting to know is that when cell require energy they use these molecules to extract the energy stored in them.
the choice of using them in the cell is dependent on the amount of energy required by the cell.
ATP upon hydrolysis yield around 7kcal/mol of energy which is quiet high required for movement of muscle fibers
GTP is a low energy yielding molecule.
NADH/FAD are used in various reaction of citric acid cycle.
below is a figure gives examples of ATP and NADH/FAD usage.
Figures explain usage of NAD , FAD and ATP