ER and Proteins

Question 1

Smooth and Rough ER

Answer 1

1. Network of membrane- enclosed tubes and flattened sacks called cisternae
2. Largest organelle in most eukaryotic cells

Question 2

Rough ER traits (think postal service)

Answer 2

1. studded with ribosomes (protein syn!!)
2. flattened like sheet shape
3. synthesizes membrane-bound lumenal proteins
4. packages and exports proteins in vesicles
5. addition of glycosylation and glycolopid anchors

Question 3

Smooth ER traits (think lipid postal service)

Answer 3

1. No ribosomes, and tube like
2. syn phospholipids and cholesterol
3. deals with lipid synthesis
4. abundant in cells with active lipid metabolism

Question 4

Protein targeting and cell topology

Answer 4

Proteins are made in one location depending on where they will end up

Ribosomes can be free or membrane bound

Question 5

cytosol is…

Answer 5

Contiguous with the INSIDE of the cell
–>nucleus
–>cytosol

Question 6

Lumen is…

Answer 6

Contiguous with the OUTSIDE of the cell
–>ER
–> Golgi
–> inside vesicles
–>outside the cell mem

Question 7

Cotranslation translocation

Answer 7

Ribosomes bind to ER while they are translating the protein, so it actively ”dumps” protein into the ER lumen

Question 8

Post Translation Relocation

Answer 8

Free ribosomes translate proteins, which are then transported to ER lumen afterwards.

Question 9

how does cotranslation translocation work? step 1-3

Answer 9

Step 1. A Signal Recognition Particle (SRP) binds to the Signal Sequence on the polypeptide chain.

Step 2. The SRP protein binds to an SRP Receptor that is attached to a Translocon.

Step 3. The ribosome binds to the translocon, which causes the SRP protein to unbind to the SRP Receptor.

• Ribosome binding to the translocon also causes the translocon to open.

Step 4. Translation resumes. Signal Peptidase cleaves the signal sequence off the growing polypeptide chain.

Step 5. Continued translating causes the growing polypeptide chain to grow into the lumen of the ER

Step 6. The finished Product is “spit out” into the Lumen of the ER

Question 10

cotranslation translocation (steps 4-6)

Answer 10

Step 4. Translation resumes. Signal Peptidase cleaves the signal sequence off the growing polypeptide chain.

Step 5. Continued translating causes the growing polypeptide chain to grow into the lumen of the ER

Step 6. The finished Product is “spit out” into the Lumen of the ER

Question 11

What is BiP? Why is it important that BiP stays inside the lumen of the ER?

Answer 11

Binding Immunoglobulin Protein,” is a molecular chaperone protein located within the lumen

primary function is to remain inside the ER lumen to effectively interact with and guide the folding of these nascent proteins as they are translocated into the ER;

Question 12

What determines if a protein will be translated on the ER or in the cytosol?

Answer 12

the presence of a specific amino acid sequence called a “signal peptide” at the beginning of the protein