The secretory pathway

Question 1

Where are most lipids synthesised?

Answer 1

At the endoplasmic reticulum

Question 2

Where is the net negative charge on a plasma membrane?

Answer 2

Inside of membrane

Question 3

How are lipids added to the endoplasmic reticulum membrane?

Answer 3

1. new lipids added to cytosolic side of ER membrane
2. phospholipid synthesis adds to cytosolic half of bilayer
3. scramblase catalyses flipping of phospholipid molecules

Question 4

How are phospholipids added to a plasma membrane?

Answer 4

1. delivery of new membrane by exocytosis
2. flippase catalyses flipping of specific phospholipids to cytoplasmic monolayer
   - translocase transfers phosphatidylserine from outer leaflet to inner leaflet
   -scramblase abolishes asymmetry
   -net equilibrium favours translocase under normal conditions

Question 5

What is the endoplasmic reticulum and describe its structure?

Answer 5

-a dynamic network that’s continuously breaking + reforming
-connected to the nuclear envelope
-forms hollow tubes + flattened sacs - chambers are called cisternae

Question 6

What are the 2 types of ER and how are they different?

Answer 6

-rough (RER) - outer membrane covered in ribosomes
-smooth (SER) - no ribosomes

Question 7

What are the functions of the ER?

Answer 7

-quality control
-synthesis
-storage
-detoxification

Question 8

What needs to be translocated into the ER?

Answer 8

Newly made membrane + secreted proteins

Question 9

What do chaperone proteins do?

Answer 9

Help newly synthesised linear sequences of amino acids to fold correctly

Question 10

What is the smooth endoplasmic reticulum responsible for?

Answer 10

-phospholipid + cholesterol synthesis
-steroid hormone production
-synthesis + storage of glycerides
-synthesis + storage of glycogen
-important role as a calcium store

Question 11

How does transport occur from the ER to the Golgi?

Answer 11

-in the form of vesicles + tubules
-vesicles bud off the ER + are received by Golgi
-anything in lumen or membrane of the vesicle will be transported to the new compartment

Question 12

What is the area of the membrane forming the vesicle coated with, what does it do, and what types of coat are there?

Answer 12

-coated with a cage of specialised proteins
-aids vesicle formation + has to be discarded before vesicle can fuse with target compartment
-types = clathrin, COPI, COPII