Protein transport into the ER is co-translational, and proteins are inserted via an aqueous channel into the ER. This can be studied using microsomes in an in vitro translation setup. The statements below are possible outcomes when salt conductance is measured in this system:

• A. Microsomes do not show any conductance of salt ions when isolated from the cells.

• B. Addition of puromycin will lead to increased salt conductance.

• C. Addition of puromycin will have no effect on salt conductance.

Which one of the following options has the combination of all correct statements?

Correct option is B

Explanation:

• A. Microsomes do not show any conductance of salt ions when isolated from the cells.
  This is correct. Microsomes are fragments of the endoplasmic reticulum (ER) obtained after cell lysis, and when isolated, they generally do not exhibit salt ion conductance because they do not have the machinery for active transport without cellular components.

• B. Addition of puromycin will lead to increased salt conductance.
  This is correct. Puromycin is an antibiotic that inhibits protein synthesis by causing premature chain termination during translation. However, puromycin can cause protein release from the ribosome, which may disrupt the co-translational insertion process. This disruption may increase the release of solubilized proteins into the system, potentially increasing salt conductance.

• C. Addition of puromycin will have no effect on salt conductance.
  This is incorrect. Puromycin interferes with the translation process and would likely affect the protein insertion into the ER membrane, thus influencing salt conductance. Hence, puromycin does have an effect on salt conductance.

Information Booster:

1. Microsomes are small membrane vesicles from the ER that typically do not show salt ion conductance when isolated because they lack the active transport systems of the intact cell.

2. Puromycin inhibits protein synthesis by causing premature termination of translation, which disrupts the normal insertion of proteins into the ER and can affect membrane protein function, potentially increasing salt conductance.

3. Co-translational protein insertion is the process where proteins are inserted into the ER membrane while being synthesized. Disruption by puromycin leads to less controlled insertion, influencing salt conductance.

Additional Information:

• A. Microsomes (A): Microsomes lack functional membrane channels when isolated and thus do not show salt conductance in the absence of active protein synthesis or transport mechanisms.

• B. Puromycin (B): By inhibiting protein synthesis, puromycin causes incomplete or abnormal protein synthesis, which could disrupt normal membrane function, leading to changes in salt conductance.

• C. Puromycin (C): Since puromycin disrupts translation and protein insertion, it has an effect on salt conductance, making this option incorrect.

Thus, the correct answer is 2. A and B.