Question

6. a. Explain why the antibiotics Gramicidin, Nonactin, and Valinomycin are toxic to bacteria. (You will need to do some research since those antibiotics are not described by name in your textbook.) b. Which of the three antibiotics listed in 6a above are less effective at lower temperatures? Explain your answer. 7. Generally speaking, most cells do not have proteins whose sole function is to actively transport water into or out of the cell. Why?

Answer 1

Ans a) There are many chemicals that are toxic to bacteria but in this we will specifically be discussing about gramicidin, nonacitin and valinomycin. There are different ways by which the toxic agents can affect the bacteria and one of the most prominent ways is inhibition of cell wall function. The compounds cause breach in cell wall which leads to death of the cell via internal osmotic pressure. However, when it comes to gramicidin, nonacitin and valinomycin, they acts toxic to the bacteria by altering the permeability of the cell wall. This causes leaks in the cell wall and alters the osmolarity which alters the permeability of the cell wall. This leads to entry of the compounds inside the bacterial cell and expands it till it bursts. Due to the increasing permeability of the bacterial cell membrane, it allows inorganic monovalent cations to travel through without any restrictions and destroy the ion gradient that exists between cytoplasm and extracellular environment.

b) Gramicidin is the bacterial toxin which is not effective against the bacteria at low temperature. It is because of the fact that it requires incubation at elevated temperature for prolonged time in order to act against the bacteria. It is not able to convert the cell membrane to porous and permeable form unless it is modulated by sonication and subjected to prolonged incubation at high temperature.