What is the difference between a liner and a cyclic metabolic pathway?

Question

What is the difference between a liner and a cyclic metabolic pathway?

Answer 1

I suspect you mean "linear".  Linear pathways start with a substrate and end with a product through a simple series of defined chemical modification steps.  A good example is the biosynthesis of amino acids.  Cyclic metabolic pathways are most typically associated with growth or energy utilization.  A good example of the latter is the Krebs cycle that breaks down sugar in cells and releases energy for other life processes.  The key aspect of cyclic processes is that each chemical member of the cycle is regenerated at the same rate it is consumed.  Thus, in the Krebs cycle acetate units are combined with oxaloacetate to make citric acid.  Citric acid is ultimately converted back to oxaloacetate with the release of chemical energy that is available to other processes in the cell.