08_Endomembrane System

Question 1

What organelles are included in the endomembrane system?

Answer 1

ER, Golgi complexes, endosomes, lysosomes, secretory vesicles

Question 2

Is the endomembrane system present in prokaryotes?

Answer 2

no

Question 3

What is the interior of each compartment along the endomembrane system termed? (Space between the lipid bilayer)

Answer 3

lumen

Question 4

What is the topology of the lumen similar to?

Answer 4

cell exterior

Question 5

What are membrane contact sites?

Answer 5

The are close appositions between two organelles that facilitate signalling and passage of ions & lipids from one cellular compartment to another.

At MCSs, membranes are close, but they do NOT fuse.

Question 6

Which eukaryotic organelle has MCSs with all other organelles?

Answer 6

ER

Question 7

What are cisternae?

Answer 7

stacks of flattened membrane atop each other

Question 8

Ribosomes are on the (cytosolic/lumen) surface of the RER.

Answer 8

cytosolic

Question 9

What is the ER surrounding the nuclear envelope called?

Answer 9

perinuclear ER

Question 10

What proportion of proteins are synthesized on ribosomes of the RER?

Answer 10

2/3

Question 11

Which types of proteins are synthesized on ribosomes of RER?

Answer 11

secreted proteins
integral membrane proteins
soluble proteins of organelles (e.g. for lysosomes)

Question 12

Where are nuclear proteins synthesized?

Answer 12

in the cytosol, on free ribosomes

Question 13

Where are secreted proteins synthesized?

Answer 13

ribosomes on RER

Question 14

Where are peripheral membrane proteins synthesized? How about integral membrane proteins?

Answer 14

peripheral: free ribosomes in cytosol
integral: ribosomes on RER

Question 15

Which types of proteins are synthesized on free ribosomes in the cytosol?

Answer 15

cytosolic proteins
peripheral membrane proteins
nuclear proteins
proteins incorporated into chloroplasts, mitochondria, and peroxisomes

Question 16

What determines where a particular protein will be synthesized?

Answer 16

the signal sequence –> if present, synthesis on ribosome in RER

Question 17

What is a signal sequence?

Answer 17

a sequence of amino acid residues in the N-terminus of the nascent peptides that are to be secreted or that are integral membrane proteins

Question 18

What does a polypeptide pass through in order to enter the ER lumen?

Answer 18

protein-lined pore

Question 19

What would happen if the signal sequence of a secreted protein was to be removed?

Answer 19

it wouldn’t be secreted, and would stay in the cytosol

Question 20

What protein recognizes a signal sequence?

What type of protein is this?

Answer 20

signal recognition particle (SRP)

G-protein

Question 21

What do the SRP and ribosome bind to in the process of binding of the complex to RER?

Answer 21

SRP –> SRP receptor

ribosome –> translocon

Question 22

What is the energy from the GTPase activity of the SRP and SRP receptor used for?

Answer 22

binding of the ribosome to the translocon and release of SRP

Question 23

What causes the opening of the translocon plug?

Answer 23

Once the SRP is removed, translation continues and the signal sequence inserts into the translocon channel. There, it binds the interior and this interaction the plug to move and the channel to open.

Question 24

Where is the signal sequence cleaved? What enzyme achieves this?

Answer 24

in the RER lumen; signal peptidase