Question

4. S. pneumoniae is highly dependent upon external sugars to meet its energy requirements (recall that it has neither an electron transport chain nor a TCA cycle). The transport system used by S. pneumoniae for glucose is depicted in Figure 1.

In Out Non-specific components Specific components Cytoplasmic membrane PEP Enz HPr nz Enz Enz Pyruvate Glucose Direction of P transfer Glucose 6-P ← Direction of glucose transport Figure 1. This is the phosphotransferase system that S. pneumoniae uses for the transport of glucose. (PEP is Phosphoenolpyruvate)

a. What term best describes this transport mechanism?

b. What is the immediate source of energy that drives this transport system and allows S. pneumoniae to scavenge low levels of glucose from its environment?

c. When S. pneumoniae is growing in the presence of oxygen using glucose as its energy source, which metabolic pathway (Aerobic respiration, fermentation or anaerobic respiration) would it use? Justify your answer.

d. What is the NET GAIN in ATP generated by S. pneumoniae catabolizing one molecule of glucose during this type of metabolism? Remember to take into account the cost of glucose transport. Show how you generated this answer.

Answer 1

a)

This is best known as PEP group translocation.

b)

The immediate source of energy for this system is Phospho-Enol Pyruvate. The phosphoryl group of PEP is transferred to glucose.

c)

S. pneumoniae is a facultative anaerobe; so it can grow in presence of oxygen as well. It is important to note that it does not grow very well and vigorously in presence of oxygen. It may use only the fermentation pathway for its vigorous growth.

So, even when glucose and oxygen are present, it will prefer to use the fermentation pathway.

d)

When glucose enters the cell, then glycolysis takes place. The net gain of ATP in glycolysis is 2 ATP.

One ATP is consumed when one glucose molecule is transferred in to the cell. This ATP comes from PEP.

So, the total ATP gain is (2 - 1 = ) 1 ATP.