Polymerization and the break down of a polymer are two opposite reactions. what role does a water molecule play in both of them?
a water molecule is released during polymerization, which in the formation of a bond, and it is added during the break down of a polymer, which in breaking the bond.
a water molecule is added during polymerization, which in the formation of a bond, and it is released during the break down of a polymer, which in breaking the bond.
a water molecule is added during polymerization, which in the formation of a bond, but it does not play any role during the breaking down of a polymer.

before it leaves the nucleus of a eukaryotic cell, mrna is altered in the following ways: - a cap is added to the 5' end of the mrna molecule; - a poly a tail is added to the 3' end; - introns are removed and exons are spliced together.

both anaerobic and aerobic respiration use glucose (or other carbohydrates), proteins and lipids to produce atp and nadh. cell uses those energy molecules, obtained from food and   breaks them down during the chemical reactions of respiration. in anaerobic respiration, nadh is regenerated to nad+ by enzymes lactate dehydrogenase (lactate is produced, e.g. in muscle cells) or by alcohol dehydrogenase where ethanol is produced (alcohol fermentation), while in aerobic respiration, electrons from nadh are deposited in the mitochondria to regenerate nad+ (electron transport chain. anaerobic respiration produces 2 atp per molecule of glucose compared to aerobic respiration where about 38 atp molecules are produced.