Question

What is the net ATP that is synthesized when one molecule of glucose is fermented to alcohol or lactic acid?

Answer 1

We know that fermentation is a biochemical process taking place in some organisms. The beginning of this process is similar to cellular respiration. That is the formation of pyruvic acid by the process of glycolysis where two ATP molecules are synthesized.

Complete answer:
As we know that the lactic acid fermentation is a process by which glucose and other sugars containing six carbon atoms turn into metabolite lactate and cellular energy. This type of anaerobic fermentation mostly occurs in bacteria, certain animal cells, mammalian red blood cells, and sometimes in skeletal muscles under conditions of insufficient oxygen supply to allow continuity of aerobic respiration. In this process lactic acid forms from pyruvate produced during glycolysis. Alcohol fermentation is also called ethanol fermentation because the end product in this case is ethanol. It is mostly carried out by yeast to convert simple sugars into carbon dioxide and ethanol.
It is widely used in industries to produce wine, beer, biofuel, etc. In this process, pyruvic acid is broken down into acetaldehyde and the carbon dioxide is released. The acetaldehyde thus formed, gives ethanol. NAD+ is also formed from NADH which later enters glycolysis. Two enzymes catalyze the two steps of the process. When glucose undergoes fermentation, there is a net gain of two ATP molecules that occurs in the glycolysis process. It is the same for both lactic acid fermentation and alcoholic fermentation. In glycolysis, four molecules of ATP are produced when a glucose molecule is partially oxidized to form two molecules of pyruvate. Two ATPs are utilized in the initial steps of glycolysis therefore there is a net gain of two ATP molecules.

Note:
Remember that fermentation is one of the oldest metabolic processes commonly used by prokaryotes and eukaryotes. It is also a process used in industries to manufacture various products. Various types of fermentation are used to produce the desired end product for use.