Module 8: Cytoplasmic Membrane Systems: Structure, Function, and Membrane Trafficking

Question 1

What is the biosynthetic pathway?

Answer 1

Proteins are synthesized in the ER, modified at the Golgi complex, and transported to various destinations.

Question 2

What is the secretory pathway?

Answer 2

Proteins synthesized in the ER are discharged from the cell.

Question 3

What is the endocytic pathway?

Answer 3

Materials move from the outer surface of the cell to compartments, such as endosomes and lysosomes

Question 4

What is the constitutive secretion?

Answer 4

Materials are transported in secretory vesicles and discharged in a continual manner.

Question 5

What is the regulated secretion?

Answer 5

Materials are stored in vesicles and discharged in response to a stimulus.
- Occurs in endocrine cells, pancreatic acinar cells, and nerve cells.

Question 6

What are the secretory granules?

Answer 6

It’s a site where secreted materials can be stored in large, densely packed.

Question 7

What is an autoradiography?

Answer 7

Visualizes biochemical processes by radioactively labeling molecules.

Question 8

What is GFP-tagging?

Answer 8

It allows microscope viewing of protein movement in living cells.

Question 9

What does RNA interference (RNAi) inhibit?

Answer 9

It is used to inhibit mRNA translation into proteins.

Question 10

What is the activity of the rough ER?

Answer 10

• Ribosomes bound to its cytosolic surface.
• Flattened sacs (cisternae) connected to neighbors by
  helicoidal membranes.
• Is continuous with the outer membrane of the nuclear envelope.

Question 11

What is the activity of the smooth ER?

Answer 11

• Lacks ribosomes
• Membranes are highly-curved and tubular
• Is continuous with the RER.

Question 12

What does the smooth endoplasmic reticulum include?

Answer 12

• Steroid hormone synthesis in endocrine cells of the gonad and adrenal cortex.
• Detoxification of organic
  compounds in the liver via
  oxygenases including the
  cytochrome P450 family.
• Calcium ion sequestration and regulated release

Question 13

What does the rough endoplasmic reticulum include?

Answer 13

• The nucleus and RER are near the basal surface, facing the blood supply.
• The RER is the starting point of the biosynthetic pathway for secretory
  proteins.
• About one-third of the proteins are synthesized at the RER and released
  into the ER lumen in a process called co-translational translocation.
• Remaining polypeptides synthesized on “free” ribosomes in the cytosol.

Question 14

What is the site of protein synthesis determined by?

Answer 14

By the sequence of amino acids in the N-terminal portion of the polypeptide.

Question 15

What do secretory proteins contain?

Answer 15

They contain a signal sequence at their N-terminus that directs the emerging polypeptide and ribosome to the ER membrane.

Question 16

Where do Co-translational translocation deposit proteins?

Answer 16

Into the ER lumen.

Question 17

What does the signal recognition particle bind?

Answer 17

Polypeptide and the ribosome, arresting synthesis.

Question 18

Where are ribosomes handed off to?

Answer 18

To the translocon, a protein channel embedded in the ER membrane.

Question 19

What are SPR and SPR receptors?

Answer 19

They are G proteins that
interact with one another
in their GTP-bound states;
GTP hydrolysis triggers
the release of the signal
sequence by the SRP.

Question 20

What are signal peptide removed by?

Answer 20

By signal peptidase.