Lectures 15 & 16

Front 1

1. What are the three general types of intravesicular trafficking? Briefly describe each.

Back 1

Outward flow: from ER to Golgi
Inward from Plasma Membrane inward (endocytosis)
Movement within cytosol: autophagy (programmed cell death or getting rid of aging cells)

Front 2

2. What are the critical functions of the ER discussed in this lecture?

Back 2

lipid biosynthesis: phospholipids, steroids, lipoproteins (HDL, LDL)
Membrane bound transportation of mRNA
Initial integration of lipids and proteins

Front 3

3. Secreted and membrane-bound proteins are translated on ____________ ribosomes.

Back 3

Bound

Front 4

4. Cytosolic proteins & some mitochondrial proteins are translated on ____________ ribosomes.

Back 4

Free

Front 5

5. What is a signal sequence and why is it important?

Back 5

Short (14-60) amino acid sequence at the amino (N) terminus
It determines the eventual location of a protein in the cell

Front 6

6. When a transmembrane protein is inserted into the ER, is its orientation with respect to cytosolic and non-cytosolic sided fixed, or can it turn around? And does it have any influence on the lipid components of the ER membrane?

Back 6

The orientation of a transmembrane protein is fixed with respect to the cytosolic and non-cytosolic sides and cannot turn around
The cytosolic/non-cytosolic orientation determines which phospholipids bind to the transmembrane protein (ex: oligosaccharides are non-cytosolic only)

Front 7

7. Where do vesicles that bud from the ER usually go next?

Back 7

To the Golgi apparatus for further processing

Front 8

8. How do components of the vesicular (source) membrane aid in trafficking? List the components and describe what activities they contribute to.

Back 8

Vesicular membrane components aid in budding, transport, targeting, and fusion
Coat proteins aid in vesicular budding
Vesicle motor-binding proteins aid in vesicle transport
Vesicle membrane proteins aid in targeting vesicles
Lipid constituents and Snares aid in fusing vesicles

Front 9

9. What is the function of coat proteins? What are the three major families of coat proteins? What would happen if each of these coat proteins were mutated in a way that prevented them from functioning?

Back 9

Coat proteins function to form vesicles from organelle membranes; they form lattice-like structures that pull the membrane into a bud
Three families: Clathrin (move from PM inward and between Golgi and endosomal compartments); COPI (from ER to Golgi); and COPII (move between Golgi compartments)
If these were mutated, vesicles would not be formed

Front 10

10. How is dynamin involved in vesicle formation? What do different dynamin mutations do?

Back 10

Dynamin aids specifically in clathrin budding, which forms buds from the flat and rigid PM; provides extra force in pinching off the vesicles; recruits other proteins to aid in the process
Different mutations would either enhance or block the pinching-off process

Front 11

11. What is a signal patch? Why are signal patches on the cytosolic side of vesicles important for vesicular trafficking? What proteins do they associate with?

Back 11

Signal patch is an internal signal sequences that are brought together in tertiary protein folding structure
They are on the cytosolic side to provide targeting information for vesicles
They associate with proteins of the submembrane meshwork

Front 12

12. What is the difference between Rab and SNARE proteins?

Back 12

Rab proteins on the vesicles tether Rab effector proteins to the target membrane
SNARE proteins initiate fusion between the lipid bilayer of vesicle and lipid bilayer of target membrane

Front 13

13. A vesicular SNARE binds to a target SNARE. Is fusion inevitable? Explain.

Back 13

Fusion occurs between membranes ONLY if the two lipid membranes are similar

Front 14

14. Which of the following have different compositions depending on which face of the membrane they are located (cytosolic or non-cytosolic): protein, lipid, sugars

Back 14

Lipid composition: relatively asymmetric (some similarities between cytosolic and non-cytosolic faces, but very different)
Protein composition: absolutely asymmetric (cytosolic and non-cytosolic sides are very different)
Sugar composition: absolutely asymmetric (found ONLY on non-cytosolic side)

Front 15

15. What happens to proteins in the Golgi?

Back 15

Proteins are processed through covalent modification in the Golgi
They leave the Golgi with new transport, targeting and fusion information

Front 16

16. What is the difference between constitutive and regulated secretion (from Golgi to PM)?

Back 16

Constitutive secretion is continuous, automatic transport using unregulated membrane fusion
Regulated secretion uses specialized vesicles that require a signal (hormone or neurotransmitter) for transport

Front 17

17. What is the cellular mechanism for ensuring lysosomal hydrolases are specifically (and safely) delivered to the lysosome? Why is important for these lysosomal enzymes to have a special delivery mechanism?

Back 17

Lysosomal enzymes are co-translationally transported into the rough ER, then to the Golgi, where they are tagged with a M6P group; this targets them for specific delivery to early endosomes
Lysosomal enzymes are potentially deadly to the cell as they are very acidic (they contain acid hydrolases that break down other molecules)

Front 18

18. Why are TOM and TIM proteins important for mitochondrial function?

Back 18

TOM and TIM proteins transport proteins and lipids from the nucleus to the inner membrane of the mitochondria
TOM: translocase of outer membrane
TIM: translocase of inner membrane

Front 19

19. What different activities involve endocytosis?

Back 19

Endocytosis: inward flow of vesicular material from the PM
Phagocytosis: uptake of solid particles
Pinocytosis: uptake of fluids
Receptor-mediated endocytosis
Endocytosed molecules are released in endosomes (or lysosomes) and transported into cytosol to be used in various biosynthetic processes

Front 20

20. How is vesicle formation during endocytosis similar to vesicle formation during intravesicular trafficking?

Back 20

Vesicles bud from plasma membrane using dynamin to help bud off clathrin-mediated coat proteins