Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 11

Two Types of Posttranslational Import. The mechanism by which proteins synthesized in the cytosol are imported into the mitochondrial matrix is different from the mechanism by which proteins enter the nucleus, yet the two mechanisms do share some features. Indicate whether each of the following statements applies to nuclear import (Nu), mitochondrial import (M), both (B), or neither (N). You may want to review the discussion of nuclear import in Chapter 18 before answering this question (see especially Figure 18-31).
(a)The polypeptide to be transported into the organelle has a specific short stretch of amino acids that targets the polypeptide to the organelle.
(b)The signal sequence is always at the polypeptides N-terminus and is cut off by a peptidase within the organelle.
(c)The signal sequence is recognized and bound by a receptor protein in the organelles outer membrane.
(d)ATP hydrolysis is known to be required for the translocation process.
(e)GTP hydrolysis is known to be required for the translocation process.
(f)There is strong evidence for the involvement of chaperone proteins during translocation of the protein.
(g)The imported protein enters the organelle through some sort of protein pore.
(h)The pore complex consists of more than two dozen proteins and is large enough to be readily seen with the electron microscope.