Find correct order of cotranslational translocation in endoplasmic reticulum

A. Transfer of the nascent polypeptide–ribosome to the translocon leads to opening of this

translocation channel to admit the growing polypeptide adjacent to the signal sequence, which is transferred to a hydrophobic binding site next to the central pore. Both the SRP and SRP receptor, once dissociated from the translocon, hydrolyze their bound GTP and then are ready to initiate the insertion of another polypeptide chain.

B. As the polypeptide chain elongates, it passes through the translocon channel into the ER lumen, where the signal sequence is cleaved by signal peptidase and is rapidly degraded.

C. The SRP and the nascent polypeptide chain–ribosome complex bind to the SRP receptor in

the ER membrane. This interaction is strengthened by the binding of GTP to both the SRP and its receptor.

D. The ER signal sequence emerges from the ribosome; it is bound by a signal recognition particle (SRP).

TLS Online TPP Program

#Question id: 13154

#Unit 2. Cellular Organization

In starving cells, however, such degradation would deplete essential enzymes and regulatory proteins. Lysosomes therefore also have a selective pathway, which is activated only after a prolonged fast, that imports and degrades cytosolic proteins containing the pentapeptide  , the sequence is

TLS Online TPP Program

#Question id: 13123

#Unit 2. Cellular Organization

Match the correct one?

A- COPI                           i- vesicles transport proteins from the ER to the Golgi.

B- COPII                          ii- vesicles mainly transport proteins in the retrograde direction between Golgi cisternae and from the cis -Golgi back to the ER.

C- Clathrin                      iii- vesicles transport proteins from the plasma membrane (cell  surface) and the trans-Golgi network to late endosomes.

TLS Online TPP Program

#Question id: 13122

#Unit 2. Cellular Organization

Choose the incorrect?

1- COPI vesicles transport proteins from the rough ER to the cis -Golgi; COPII vesicles transport proteins in the reverse s Direction.

2- The KDEL receptor binds more tightly to its ligand ar low pH, and it is thought that the receptor is able to bind KDEL peptides in the cis-Golgi but to release these peptides in the ER because the pH of the Golgi is slightly lower than that of the ER.

3- The KDEL sorting signal is recognized and bound by the KDEL receptor, a transmembrane protein found primarily on small transport vesicles shuttling between the ER and the cis -Golgi and on the cis-Golgi reticulum.

TLS Online TPP Program

#Question id: 13121

#Unit 2. Cellular Organization

--------- act as a nuclear export factor and directs the associated mRNP to the central channel of the NPC by transiently interacting with FG- nucleoporins.

TLS Online TPP Program

#Question id: 13120

#Unit 2. Cellular Organization

Match the correct one?

Target organelle	Location of sequence within protein	Removal of sequence	Nature of sequence
1- ER	i- N- terminal	a- yes	P- Core of 6-12 hydrophobic aa often preceded by one or more basic ammo acids (Arg, Lys)
2-Mtochrondria matrix	ii- N- terminal	b- yes	Q- Multiple different kinds;  rich in Lys and Arg residues
3-Chloroplast stroma	iii- N- terminal	c- no	R- Lys and arg one side and other side hydrophobic aa
4-Nucleus	iv-varies	d- yes	S- Generally rich in ser and thr, poor in glu and asp

TLS Online TPP Program

#Question id: 13119

#Unit 2. Cellular Organization

Ions, small metabolites, and globular proteins up to about ---------- can diffuse passively through the central aqueous region of the nuclear pore complex.