(c) You perform a third experiment, in which you àdd böll and ER membrane vesicl

Question

(c) You perform a third experiment, in which you àdd böll and ER membrane vesicles to your protein-synthesizing system and find that translation of the prolactin mRNA now produces a polypeptide 199 amino acids long. How can you explain this result? Where would you expect to find this polypeptide? 19-11 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 nei- ther (N). You may want to review the discussion of nuclear import in Chapter 16 before answering this question. (a) The polypeptide to be transported into the organelle has a specific O- short stretch of amino acids that targets the polypeptide to the 6 organelle. and is cut off by a peptidase within the organelle. tein in the organelle's outer membrane. (b) The signal sequence is always at the polypeptide's N-terminus (c) The signal sequence is recognized and bound by a receptor pro- (d) ATP hydrolysis is known to be required for the translocation (e) GTP hydrolysis is known to be required for the translocation () Chaperone proteins are involved during translocation of the (g) The imported protein is transported in a membranous vesicle (h) The imported protein enters the organelle through a protein et- tic process. process protein. prior to import. pore that consists of more than two dozen proteins and is large ed enough to be readily seen with the electron microscope. e a

Explanation / Answer

a) Both (B)

b) Mitochondrial import(M)

c) Mitochondrial import(M)

d) Both (B)

e) Neither(N)

f) Neither(N) Chaperones are primilarly involved with protein folding

g) Neither(N) Membrane vesicular transport is observed in protein transloction into ER.

h) Nuclear Import (Nu)

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