Question

In bacteria, the sec machinery involved in bacterial protein secretion ___.

a. translocates fully folded proteins across the cell wall transfers secreted proteins directly from the cytosol of bacteria into the cytosol of host cells
b. maintains a low concentration of secreted protein in the cytosol by linking protein synthesis to secretion
c. delivers secreted proteins directly across the inner and outer membranes of gram negative bacteria in a single step
d. concentrates the protein to be secreted within the cytosol of bacterial cells in order for the protein to be fully folded prior to secretion

Answer 1

The Sec machinery in bacteria does not deliver proteins across both bacterial membranes in a single step; it primarily transports proteins across the plasma membrane into the periplasmic space, especially in gram-negative bacteria.

Step-by-step explanation:

In bacteria, the Sec machinery involved in bacterial protein secretion does not deliver secreted proteins directly across the inner and outer membranes of gram-negative bacteria in a single step. Instead, the Sec machinery transports proteins through the plasma membrane into the periplasmic space. In gram-negative bacteria, proteins need to cross two membranes, and this usually occurs in a stepwise fashion, with the inner membrane passage facilitated by the Sec machinery, followed by separate mechanisms for passage through the outer membrane.

The Sec pathway is highly conserved across both prokaryotes and eukaryotes and is essential for the translocation of proteins across the cytoplasmic membrane. In gram-negative bacteria, additional systems such as type III secretion systems or efflux pumps may further handle protein transport or export, especially in relation to pathogenesis and antibiotic resistance.