Question

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, mitochondrial import, both, or neither. Sort each statement into the appropriate bin.
1. The polypeptide to be transported into the organelle has a specific short stretch of amino acids that targets the polypeptide to the organelle.
2. The imported protein enters the organelle through some sort of protein pore
3. The pore complex consists of more than two dozen proteins and is large enough to be readily seen with the electron microscope.
4. ATP hydrolysis is known to be required for the translocation process
5. The signal sequence is always at the olypeptide's N-terminus and is cut off by a peptidase within the organelle
6. The signal sequence is recognized
GTP hydrolysis is known to be required for the translocation process
7. There is strong evidence for the involvement of chaperone proteins polypeptide's N-terminus and isctand bound by a receptor protein inrequired for the translocation during translocation of the protein the organelle's outer membrane process.
Nuclear import Mitochondrial import Both Neither

Answer 1

Answer:

Nuclear import:

1. GTP hydrolysis is known to be required for the translocation process

2. The pore complex consists of more than two dozen proteins and is large enough to be readily seen through electron microscopy

Mitochondrial import:

1. ATP hydrolysis is known to be required for the translocation process

2. The signal sequence is always at the polypeptide's N-terminus and is cut off by a peptidase inside the organelle

3. There is strong evidence for the involvement of chaperones during the translocation process

4. The signal sequence is recognized and bound by a receptor protein in the organelles outer membrane

Both:

1. The polypeptide to be transferred into the organelle has a specific short stretch of amino acids that targets the polypeptide to the organelle

2. The imported protein enters the organelle through some sort of protein pore

Explanation: