Question

According to Peter J. Russel (iGenetics, 2nd international ed., Page 123) in the process of Translation, the ribosome is translocated along the mRNA. But during the co-translational translocation of the protein to endoplasmic reticulum, the ribosome get attached to the ER membrane protein. Then how it can move along with the mRNA?

Answer 1

The whole protein complex (mRNA, ribosome, protein+ signal sequence, and signal recognition particle) to ER.
-Signal recognition particle comes off (to the cytosol)
-Signal sequences comes off (to inside of ER)
-Now protein can finish synthesis on the surface of ER.
-Synthesized Protein now enter ER.
http://www.youtube.com/watch?v=PUy_Em5dXmc

Answer 2

you did not get my query at all

Answer 3

"It is therefore likely that the tRNAs are pulling the mRNA through the ribosome via codon-anticodon interactions in the course of translocation."

-According to this paper: http://www.jbc.org/content/269/48/30713.full.pdf

In other words, the attached ribosome need not move along the mRNA to synthesize a polypeptide. Though this appears to contradict what your textbook says, my guess is that relatively speaking, the ribosome does appear to "move along" the mRNA (from the mRNA's point of view)? Hope this helps.

Answer 4

Interesting question!

Answer 5

Yes I would agree with @kma230. It's a similar idea to say the growth of neurons via actin treadmilling. While the actin is constantly polymerizing and depolymerizing during its interaction with myosin, protrusive growth occurs only when it is anchored to the extracellular matrix via the cytoskeleton. This allows the actin to move purposefully relative to the cell membrane.

Dunno if that helps, but its an interesting thought nonetheless.