Some organisms can ferment glucose but not sucrose How can y

Some organisms can ferment glucose but not sucrose. How can you explain this knowing sucrose is made up of glucose and fructose? Why can’t the bacteria ferment the glucose present in the sucrose molecule if they are able to ferment glucose?

Solution

Every organims requires an enzyme to break down or digest a foreign material in the cell. These enzymes are specific to their substrate and any chance of substrate-swithcing does not take place. This phenomenon of substrate specificity holds true for proteins, fats and sugars as well. For example, there is utmost requirement of enzyme pepsin for digestion of proteins into smaller polypeptides. Further, collagenase is absolutely required for digestion of matrix made up of collagen.

Similarly, the enzyme sucrase is indispensably require for digestion/break down of sucrose. Biochemically, sucrose is made up of smaller subunits of glucose and fructose. Whereas most of the bacteria are comprised of enzymes for glucose metabolism, the enzyme sucrase specific for sucrose metabolism is not present in every microbe. Thus, not every microbe is capable of fermenting or breaking down this sugar.

Similarly, if a media is there in which both sucrose and glucose are present, the bacteria will be able to digest only the free glucose present but not the polymerized glucose present in the sucrose structure. Hence, no fermentation of bound-glucose (in sucrose polymers) will take place.