Question

In homofermentative lactococci, __________ moles of lactic acid are produced from the metabolism of one mole of lactose.

• A. 1
• B. 2
• C. 4
• D. 6

Hint:

Keep this stoichiometry in mind:
- 1 mole of hexose (glucose/galactose) $\rightarrow$ 2 moles of lactic acid (homofermentation).
- 1 mole of lactose (disaccharide) $\rightarrow$ 2 moles of hexose $\rightarrow$ 4 moles of lactic acid.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Lactic acid bacteria (LAB) ferment carbohydrates via different biochemical pathways depending on their enzymatic machinery.
Homofermentative lactic acid bacteria, such as Lactococcus lactis, utilize the Embden-Meyerhof-Parnas (EMP) glycolytic pathway to convert sugars into lactic acid.
Detailed Explanation:
In homofermentative lactococci, lactose metabolism proceeds through a well-defined sequence:
- First, one mole of the disaccharide lactose is transported into the bacterial cell, typically via the phosphoenolpyruvate-dependent phosphotransferase system (PEP-PTS).
- It is then cleaved by the enzyme phospho-\(\beta\)-galactosidase to yield one mole of glucose and one mole of galactose-6-phosphate (which is converted to glucose-6-phosphate through the tagatose-6-phosphate pathway).
- This hydrolysis yields a total of two moles of hexose sugars from each mole of lactose.
- Under homofermentative metabolism, each mole of hexose enters the Embden-Meyerhof-Parnas (EMP) pathway and is glycolyzed into two moles of pyruvate.
- Finally, these pyruvate molecules are reduced by lactate dehydrogenase to yield two moles of lactic acid.
- Since one mole of lactose yields two moles of hexose, the total yield of lactic acid is calculated as:
\[ 2 \text{ moles of hexose} \times 2 \text{ moles of lactic acid/hexose} = 4 \text{ moles of lactic acid} \]
Therefore, the metabolism of one mole of lactose by homofermentative lactococci produces exactly four moles of lactic acid.
Final Answer:
In homofermentative lactococci, 4 moles of lactic acid are produced from one mole of lactose. Hence, the correct option is (C).