Question

recall that ph expresses the concentration of protons (h+) in a solution. most proteins denature - meaning that they lose tertiary structure and unfold - at ph values below 5 or over 10. protein denaturation is life - threatening, so most cells maintain an intracellular ph of 7.0 - 7.6. how is it possible, then, that some bacteria can live in your stomach, where the ph is 1.0, or in extremely basic habitats where the surrounding water has a ph of 12 or even 13? choose the single best answer.

their membrane proteins do not have tertiary structures, so are not susceptible to denaturing based on low or high ph.

denaturing occurs at low and high ph because the presence of many or few protons disrupts the bonds and interactions that stabilize protein folding.

the structure of their cell membranes strictly regulates the transport of protons into and out of the cell.

Explanation:

The cell membranes of bacteria can regulate proton transport. This allows them to maintain an appropriate intracellular pH and protect their proteins from denaturing, even in extreme - pH environments. The first option is incorrect as membrane proteins generally have tertiary structures. The second option just explains why denaturing occurs at extreme pH but not how bacteria survive.

Answer:

The structure of their cell membranes strictly regulates the transport of protons into and out of the cell.