Soluble Protein Import into the Endoplasmic Reticulum

Question 1

All protein synthesis begins with

Answer 1

Free cytosolic riboosomes

Question 2

What does the Endoplasmic Reticulum Signal Sequence contain?

Answer 2

Non-Polar amino Acids (Hydrophobic) on the N-Terminus of a polypeptide

Question 3

Free cytosolic ribosomes are brought to _____ _______ where is will continue to polypeptide synthesis

Answer 3

Endoplasmic Reticulum

Question 4

Free Cytosolic Ribosomes with the appropriate signal sequence can…

Answer 4

Be transported to the Nucleus and Mitocondria

Question 5

If free ribosomes shave no signal sequence, where do they transport?

Answer 5

If there is no signal sequence the free ribosomes remain in the cytoplasm

Question 6

Membrane-bound Ribosomes (Bound to the ER) with the appropriate signal sequence can be transported to…

Answer 6

From the endoplasmic Reticulum, the proteins can be transported to the Golgi Apparatus, Lysosomes, Plasma Membrane, or be secretory vesicles

Question 7

What directs the Free Cytosolic Ribosomes to the ER?

Answer 7

An ER Signal Sequence and SRP

Question 8

Signal Recognition Particle:

Answer 8

Binds ER single sequence of Protein being transported, and translation is paused

Question 9

SRP Receptor

Answer 9

is a transmembrane protein in the ER whose cytosolic side recognizes SRP for binding. the SRP particle is removed

Question 10

Nascent: Protein Translocator

Answer 10

The polypeptide is threaded into the lumen via a translocation channel and translation resumes

Question 11

Signal Peptidase

Answer 11

when the polypeptide is through the translocator, the translocator closes and the enzyme cleaves the signal sequence from the N-Terminus of the polypeptide

Question 12

When the signal sequence is cleaved

Answer 12

The polypeptide will continue to fold in the ER lumen

Question 13

Do chaperone proteins play a role in ER Import?

Answer 13

yes, the chaperone proteins in the ER help proteins fold into their correct conformation and prevent misfolded proteins from exiting the ER

Question 14

UPR: Unfolded Protein Response:

Answer 14

Accumulation of Misfolded proteins in the ER results in more production of Chaperones.
- The cell will inhibit protein synthesis and UPR will slow translation and also activate genes that encode for chaperone proteins

Question 15

Are proteins folded in the cytosol before import or in the ER Lumen after import?

Answer 15

Folded when they enter the ER Lumen

Question 16

where is the Signal Sequence on the ER Protein?

Answer 16

N-Terminus
-includes a string of hydrophobic amino acids

Question 17

how does the Er recognize incoming ER proteins? What is responsible and where is it located?

Answer 17

Signal recognition particle bring protein to the ER and binds to the SRP Receptor

Question 18

What is the function of the translocator?

Answer 18

to bring the polypeptide into the ER Lumen

Question 19

ER Signal Sequence

Answer 19

Hydrophobic amino acids for soluble proteins on the N-Terminus

Question 20

Is signal sequence cleaved?

Answer 20

yes, it is cleaved by signal peptidase enzyme

Question 21

Is the protein imported in a folded or linear conformation?

Answer 21

Protein is imported in a Linear Conformation

Question 22

What are the proteins required of ER Transport?

Answer 22

-Signal recognition particle
-SRP Receptor
-Translocator
-Signal Peptidase
-Chaperones

Question 23

Is energy required for this process?

Answer 23

No